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18 Cards in this Set

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(SYSTEM: IMMUNOLOGY, GENERAL PRINCIPLES); An experimental study on acne is performed using biopsy samples from acne pustules. The electron micrograph above illustrates one of the types of cells present in the wall of the pustules. Which of the following characteristics would most strongly suggest that the cell depicted above is a phagocytically active macrophage?
Presence of receptors for IgG and complement
This is conceptually a two-part question. The first task is to identify the type of cell illustrated in the elctron microscopic image. Characteristics that suggest that it is a macrophage include the large, irregular-shaped nucleus (without being either obviously multi-lobed like a neutrophil or bilobed like an eosinophil or basophil); absence of granules (which would have suggested a neutrophil, eosinophil, or basophil); presence of many secondary lysosomes (indicating the capacity for phagocytosis); and the irregularly formed cell outline (corresponding to the pseduopodia seen in amoebic cells). Once the cell is identified as a macrophage, the next job is to pick out the criterion in the questions that best substantiates the idea that this type of cell is currently phagocytically ctive. Macrophages interact with a segment of the heavy chains of the IgG molecule, the Fc domain. Thus, the macrophage receptors for IgG are called Fc receptors. Complement receptors are also found on the macrophage surface. Phagocytosis occurs more readily when both of these components are present. Neutrophils and eosinophils have similar receptors: neutrophils assist macrophages in destruction of bacteria, while eosinophils respond to parasitic infections. *Collagenase can be demonstrated immunologically in a number of cells, including eosinophils, mast cells, osteoclasts, and fibroblasts. *Microvilli or pseudopodial extensions are common in macrophages, but also may be found on other cells, such as fibroblasts and epithelial cells that phagocytize material. *MY INCORRECT ANSWER: Secondary lysosomes are a feature of macrophages, but may also be found in fibroblasts and epithelial cells. *The shape of the nucleus has little to do with phagocytic activity.
(SYSTEM: MICROBIOLOGY GENERAL PRINCIPLES); A 16-year-old high school cheerleader presents with low grade fever, pleuritic pain, and a non-productive cough. Her serum agglutinates Streptococcus salivarius strain MG. Therapy should include which of the following?
The patient has primary atypical pneumonia caused by Mycoplasma pneumoniae. These organisms are fastidious and difficult to culture in the laboratory; however, serodiagnosis can be most helpful. Patients produce one or two heterophile antibodies during the course of the infection: one agglutinates human O+ RBCs in the cold (cold hemagglutinins) while the other causes the agglutination of a strain of Streptococcus salivarius termed strain MG (the Strep MG agglutinins). Mycoplasma are susceptible to the macrolide family of antijbiotics (erythromycin, clarithromycin, etc.). These organisms lack a cell wall; hence they are indifferent to antibiotics that interfere with peptidoglycan syntehsis, such as penicillin and *MY INCORRECT ANSWER: ampicillin *Oxygen and external cooling are therapeutic measures that are used in the treatment of severe respiratory diseases, such as pneuococcal pneumonia. *Ribavirin is used in the treatment of respiratory syncytial virus infection in infants. This is the most common cause of hospitalization for respiratory disease in the very young, probably because aerosol administration of the antiviral compound is best accomplished in a hospital setting.
(SYSTEM: IMMUNOLOGY, GENERAL PRINCIPLES); A 52-year-old woman reports to her family practitioner for an annual physical examination. She has been experiencing periods of heat intolerance, which she has attributed to the menopause. On examination, her physician notices that her eyeballs seem to be unusually protuberant and she has sinus tachycardia. Blood tests confirm that her T3/T4 levels are elevated. What is the mechanism of pathogenesis of her condition?
Type II non-cytotoxic hypersensitivity
The patient described has Graves disease, which is an autoimmune form of hyperthyroidism produced by autoantibodies directed against TSH receptor. These antibodies are called LATS (long-acting thyroid stimulator) and stimulate thyroid function, resulting in the release of thyroid hormones. This is a type II non-cytotoxic hypersensitivity, in which antibodies occupy the TSH receptor sites and provide unrelenting stimulation to the thyroid cells, which ultimately become exhausted an unable to further secrete T3 and T4. It is distinctive from other forms of type II hypersensitivity in that the pathology does not involve complement-mediated lysis of the affected cells. *Type I hypersensitivity is also known as IgE-mediated, immediate hypersensitivity, or atopic allergy. Its symptoms are manifest within minutes of reintroduction of an allergen, and are caused by cross-linkage of IgE molecules bound to mast cells and basophils and the resulting degranulation of those cells causing tissue damage. *MY INCORRECT ANSWER: Type II cytotoxic hypersensitivity involves autoantibodies, which bind to specific tissues or cells, activate complement, and cause the destruction of the underlying tissue. *Type III hypersensitivity is also known as immune complex hypersensitivity. It is caused by the deposition of complexes of antigen and antibody, causing complement activation in the small vasculature where the complexes are cleared from the circulation. The damage is mediated by complement activation, and is system-wide rather than organ-specific. *Type IV hypersensitivity is also known as T cell-mediated or delayed-type hypersensitivity. It is mediated by TH1 cells and macrophages and is manifested 48-72 hours following reintroduction of protein antigens.
(SYSTEM: MICROBIOLOGY GENERAL PRINCIPLES); A 70-year-old man with a hisjtroy of prostate cancer presents with a chief complaint of pain on the right side of his chest for the past several days. He has been receiving external beam radiation to spinal metastases of his prostate cancer forj the past several weeks. On examination, there is marked tenderness along the right side of the chest wall in a 4-6 cm stripe from the midline to the flank. Multiple small vesicular lesions are visible in this area on an erythematous base. Some of the lesions are fluid-filled, and some are crusted. How do members of the virus family responsible for his condition produce messenger RNA?
By transcribing the genomic DNA
This is a classic case of shingles, a stress-activated secondary disease caused by reactivation herpes zoster. Herpes viruses are DNA viruses that use the mechanism used by our own cells to transcribe an RNA strand from their genomic DNA and use the transcribed RNA as messenger RNA. *MY INCORREC T ANSWER: Positive RNA viruses use direct translation from the genome to make protein, not messenger RNA. *Retroviruses produce a double-stranded DNA intermediate to affect genomic duplication. *Positive-sense RNA viruses produce a negative-sense intermediate to produce a genomic duplicate. *Negative-sense RNA viruses produce a positive-sense intermediate to produce messenger RNA and a genomic duplicate. *Transcription from proviral DNA is used by the retroviruses to make messenger RNA. *Genomic RNA used directly on the ribosomes characterizes the production of messenger RNA by positive-sense RNA viruses.
(SYSTEM: IMMUNOLOGY, GENERAL PRINCIPLES); A patient with Epstein-Barr virus lymphoma enrolls in an experimental protocol to stimulate production of CD8+ cells specific for his EBV-transformed cells. His peripheral blood cells are tested with a battery of anti-HLA, A, B, and C antibodies, followed by addition of complement, and trypan blue dye. The wells of the microtiter plate in which dye was taken up by the cells is shown below: (*picture*). Which of the following molecules implanted into the membrane of a culture of tissue fibroblasts enriched for expression of costimulatory molecules would serve to stimulate the most effective cytotoxic killing?
EBNA plus HLA-A1
CD8+ cytotoxic T cells are stimulated by the presence of endogenously produced peptides presented in the groove of a class I MHC molecule. IN the presence of costimulatory molecules, such as B7 and CD 28, these killer cells can be stimulated directly in the absence of TH cells. The test performed in the microtiter plate here is a cytotoxicity assay to define the class I haplotype of the cancer patient. Cells exposed to specific anti-class I antisera plus complement will become leaky and take up dye molecules. The haplotype of this patient is HLA-A1/7, HL-B1/7, and HLA-C2/3, so any of these MHC molecules loaded with peptides from the intracellular virus would stimulate a killing response. The peptides loaded into the groove of the class I molecule must be endogenously synthesized: whole virus will not be effective. EBNA is a molecule found on the membrane of Epstein-Barr virus transformed cells and would be a good candidate for CTL recognition. *Whole Epstein-Barr virus by itself would not serve as a stimulus for cytotoxic killing. Small peptides produced during viral infection and transported to the cell membrane in the groove of class I MHC molecules serve as the stimulus for this response. *HLA-A1/7 by itself would not serve as a stimulus for cytotoxic killing in this patient. This haplotype is syngeneic for the patient and would not be recognized by itself as foreign. *HLA-B2/3 would stimulate a cytotoxic response in this patient, but not one which would be directed against EBV-transformed cells. This haplotype is allogeneic to the patient, so it would stimulate a cytotoxic response, but not the desired one. *MY INCORRECT ANSWER: HLA-C2/3 would not serve as a stimulus for cytotoxic killing in this patient. This haplotype is syngeneic for the patient and would not be recognized by itself as foreign.
(SYSTEM: MICROBIOLOGY GENERAL PRINCIPLES); A 6-month-old infant is rushed to the emergency department because he seems to be having touble breathing. His mother was breast-feeding the child when she noticed that he seemed to be unable to suckle strongly, his eyelids were drooping, and his breaths were shallow and irregular. The child is placed on respiratory support immediately. The mother acknowledges adding honey to the infant's first solid foods. Where is the genetic coding for this toxin located?
lysogenic phage genome
This child has floppy baby syndrome, caused by ingestion of the spores of Clostridium botulinum, germination of the organism in the gut of the infant, and subsequent production of the botulinum toxin, which causes a flaccide paralysis by blocking release of acetylcholine in cholinergic synapses. The genetic coding for production of this neurotoxin is found in the genome of a lysogenic phage, and therefore is produced only in virus-infected bacterial cells. Other medically important attributes that are encoded in this way include the O antigen of Salmonella, the erythrogenic exotoxins of STreptococcus pyogenes, and the diptheria toxin. *The bacterial chromosome is the location of all essential genes in the bacterium. Loss of any essential gene will result in the death of the organism. Although most exotoxins are encoded on bacterial plasmids, endotoxin production and the cholera toxin are chromosomally encoded. *An episome is a plasmid which has become stably integrated into the bacterial chromosome. This is the mechanism by which Hfr cells arise in nature, but is not know to play a role in exotoxin production in bacteria. *MY INCORREC T ANSWER: Plasmids are extrachromosomal circles of DNA that replicate autonomously and carry genes for most exotoxins of Streptococcus pyogenes and the diptheria toxin are not encoded on plasmids, but in the genomes of lysogenic phages. *Transposons are mobile segments of DNA, which are capable of mediating their own movement within and between strands of DNA inside cells. Transposition is believed to be responsible for the arising of multiple drug resistant-plasmids, but is not believed to play a role in exotoxin production.
(SYSTEM: MICROBIOLOGY GENERAL PRINCIPLES); A colony of Neisseria gonorrhoeae is isolated on Thayer-Martin medium. Over the course of ten generations in culture, this strain produces a homogeneous antigenic type of pili. Lysates froma culture of N. gonorrhoeae with a different pilus type are added to the stable colonies. After overnight incubation, the bacteria are cloned, and their pilus expression is analyzed. In 50% of the new colonies, a new antigenic form of pili is now expressed. What has happened in these cultures?
natural transformation
When lysates of bacteria are added to cultures, the DNA can be taken up by the living cells by the process of transformation. Many bacteria are capable of transformation following laboratory treatments that allow them to endocytose extracellular DNA. Only a few medically important species undergo natural transformation: Haemophilus species, Streptococcus species, Neisseria gonorrhoeae, and Helicobacter pylori. These organisms are capable of taking up free DNA without pretreatment. Other bacteria may be induced to undergo artificial transformation in the laboratory. In N. gonorrhoeae, it is estimated that up to a million antigenically distinct types of pili can be formed by recombination of expressed and silent DNA sequences within aj cells, as well as by uptake of DNA from other cells in the environment. Since the pili are structures on the outside of the bacteirum, changing of their antigenic composition during an infection gives the organism an advantage against the host's immune response. *MY INCORRECT ANSWER: Conjugation is a mechanism of genetic exchange in bacteria that involves cell-to-cell contact and the donation of DNA from a donor cell to a recipient. Since this experiement stipulates that the lysates of cells are added to the cultures, there can be no cell-to-cell contact. *Generalized transduction is the mechanism of genetic exchange in bacteria that involves the presence of a virus vector. In this manner, virulent phage can accidentally transfer DNA from one bacterium to another. There is no mention of the presence of viruses in this question stem. *Site-specific recombination is the mechanism by which two circular pieces of DNA can be combined with one another. It occurs during the process of specialized transduction during the life cylce of lysogenic viruses, during transposon movement, and is the means by which the Hfr chromosome is formed. It is not a means by which extracellular linear pieces of DNA are imported into cells, as described here. *Specializxed transduction is the mechanism of genetic exchange in bacteria that involves transfer of bacterial genes from cell-to-cell using a lysogenioc virus. There is no mention of viruses in the question stem here.
(SYSTEM: IMMUNOLOGY, GENERAL PRINCIPLES); A couple brings their son into a specialty clinic for evaluation of recurrent bacterial infections involving the respiratory tract. Causative agents have included Streptococcus pneumoniae, and Hemophilus influenzae, in spite of current immunization status. Other family members have a similar disorder, as noted in the pedigree above. Which of the following is the most likely diagnosis?
Bruton agmmablobulinemia
Several immunodeficiency disorders have X-linked genetics, including Bruton agammablobulinemia, Wiskott-Aldrich syndrome, and some cases of severe combined immunodeficinecy diseases. Bruton agammaglobulinemia is characterized by recurrent respiratory infections caused by pyogenic organisms. *Common variable immunodeficiency is a relatively common, but probably heterogenous, group of acquired and familial diseases. It is distinct from X-linked (Bruton) agammaglobulinemia. *DiGeorge syndrome is due to a developmental malformation of the third and fourth pharyngeal pouches, leading to failure of the thymus, and sometimes the parathyroids, to develop. Defective cellular immunity and anormalities of calcium metabolism are typical. *Herediatary angioedema is a usually receissive genetic diseasse causxed by deficiency of C1 esterase inhibitor. *MY INCORRECT ANSWER: Isolated IgA deficiency can be acquired or genetic, but is NOT USUALLY X-LINKED.
(SYSTEM: MICROBIOLOGY, RESPIRATORY); A 9-month-old infant is brought to the pediatrician by her mother during a winter month. The child has a febrile illness, which has now become associated with labored breathing and wheezing. Auscultation of the chest reveals expiratory wheezes over both lung fields and there is clear tachypnea and tachycardia. What is the first thing that this causative agent virus does upon entering a cell?
It transcribes its genome into messenger RNA using a virion-associated RNA-dependent RNA polymerase
This child has bronchiolitis caused by respiratory syncytial virus. This is a negative-sense, single-stranded RNA virus in the Paramyxovirus family. Negaitve-sense RNA viruses must carry an RNA-depended RNA polymerase within their nucleocapsid so that their genome can be converted into a positive-sense version, which will then be used on the ribosomes to creaste protein. The first thing such a virus does upon entering a cell is to use its own polymerases to create mRNA (positive-sense RNA) so that proteins can be created. *Reverse transcription of its genome into double-stranded DNA using a virion-associated RNA-dependent DNA polymerase would be a description of the first thing that retroviruses must do on entering a cell. These are single-stranded, positive-sense RNA viruses that carry a reverse transcriptase (RNA-dependent DNA polymerase) in their nucleocapsid, create double-stranded DNA in this way, and finally parasitize the chromosomes of the host cell. *Transcribing its genome into messenger RNA using cellular DNA-dependent RNA polymerases present in the nucleus would be a description of what double-stranded DNA viruses must do on entering a cell. Poxviruses, which are double-stranded DNA viruses, complete this step in the cytoplasm, using a virion-associated DNA-dependent RNA polymerase. *MY INCORRECT ANSWER: Translating proteins directly from its genome using cellular ribosomes would be a characteristic of the first step in the life cycle of a positive-sense RNA virus. These viruses do not need to carry a polymerase in their nucleocapsid because their genomic RNA is directly useable on the ribosomes. *The negative sense strand of the genome of double-stranded RNA viruses such as reovirus or rotavirus is used as a temploate by virion core enzymes to synthesize individual mRNAs.
(SYSTEM: MICROBIOLOGY GENERAL PRINCIPLES); A 34-year-old HIV-positive man without previous opportunistic infections presents complaining of dyspnea with daily activity. He states that he has had a mild cough and fever but denies having had chills, sputum production, or chest discomfort. Physical examination is remarkable for oral thrush and a few small, nontender cervical lymph nodes. A chest x-ray film reveals bilateral interstitial infiltrates, and bronchoalveolar lavage reveals small silver-staining cysts. IN which other patient population in the U.S., is this organism a frequent cause of a life-threatening pneumonia?
premature infants
This patient has Pneumocystis carinii pneumonia, the most common atypical pneumonia in AIDS patients. The next most common pool of at-risk individuals consists of premature infants. *MY INCORRECT ANSWER: Bone marrow transplant patients would be immunologically compromised, and might be a second-at-risk group (behind premature infants), but would not be the first choice on this list. *Hospitalized adults on antibiotic therapy might be slightly immunologically compromised or stressed, but are not the major patient pool at risk for this infection in the U.S. *Late-term pregnant women are not immunologically compromised and would not be at risk. *Normal adults in periods of stress are not particularly susceptible to opportunistic pathogens. *Preschool children have normal rates of exposure to P. carinii, as would any adult, but are not susceptible to serious pneumonia with this agent unless they are immunologically suppressed. *Sexually active adolescents would have the same infection rates as normal infants and adults, but again would not be susceptible to life-threatening pneumonia. jP. carinii is transmitted via aerosols, not sexual activity. *Third-trimester fetuses are not susceptibe to infection with this fungus, although they may become infected in utero with HIV.
(SYSTEM: MICROBIOLOGY, RESPIRATORY); A newborn infant develops respiratory distress shortly after delivery and is taken to the neonatal intensive care unit for observation. The next day, she become febrile with persistent dyspnea and coughing. Sputum recovered by the respiratory therapist reveals numerous neutrophils and gram-negative rods that grow as pink colonies on MacConkey's agar. The infective organism most likely belong to which of the following genera?
Essentially, this question tests your understanding of MacConkey's agar and your knowledge of the biochemical characteristics of the Enterobacteriaceae. MacConkey's agar is used to identify organisms that ferment lactose, and consequently grow as pink colonies. Escherichia coli is one of several lactose-fermenting Enterobacteria, along with Serratia, Klebsiella, and Citrobacter species. Neonatal pneumonia due to aspirated E. coli during delivery is not uncommon, and it should be treated with a third-generjation cephalosporin and/or aminoglycoside. *Proteus species are motile, non-lactose fermenting bacteria that characteristically swarm on an agar plate. Proteus infections generally affect the genitourinary tract, but Proteus is an important nosocomial pathogen. *MY INCORRECT ANSWER: Pseudomonas species are normally widespread in nature, but may form a small portion of the bowel flora. Pseudomonas utlizes cytochrome oxidase for energy production; it does NOT ferment any sugars. *Salmonella species are non-lactose fermenters that may produce inflammatory diarrheas. They are normally distinguished from the other Enterobacteriaceae by their ability to produce acid and gas from dextrose-containing media. *Shigella species are non-motile, non-lactose fermenting bacteria that live exclusively in the gastrointestinal tract of primates. They typically produce dysentery.
(SYSTEM: MICROBIOLOGY, NERVOUS); A 38-year-old AIDS patient presents to his physician's office in Kansas City, Missouri, complaining of fever for the past week and an increasing headache. He also states that sunlight hurts his eyes and that he has been feeling nauseated and weak. His past medical history is significant for Pneumocytis pneumonia and a total CD4 count of 89/mm3. Current medications are trimethoprim/sulfamethoxazole and indinavir. Cerebrospinal fluid (CSF) reveals 4 WBC/mm3, and budding encapsulated yeast forms grown on Sabouraud's agar. Which of the following is an accurate description of the morphology of the infectious form of the organism responsible for the man's illness?
Broad-based budding yeasts
This is a class case of Cyrptococcus neoformans meningitis. Clues included the patient population (HIV positive), geographic area (Mississippi and Missouri river beds), and diagnostic form (encapsulated yeast). Cryptococcus is a monomorphic fungus, unlike many of the class pathogens within the fungal group, so the encapsulated yeast form would be found both in clinical specimens and in the environment as the infectious form. *MY INCORRECT ANSWER: Broad-based budding yeasts would be the forms expected to be found in clinical specimens (not environmental forms) from patients infected with Blastomyces dermatitidis, which is far more likely to present with skin and bone lesions than with meningitis. *Buydding yeasts in a "pilot's wheel" arrangement would be the form expectyed to be found in clinical specimens (not environmental forms) from patients infected with Paracoccidioides brasilinensis, which is limited in geographic region to Central and South and typically presents as a primary pulmonary disease. *Cylindrical arthroconidia would be the transmission forms characteristic of Coccidioides immitis, which may be a cause of fungal meningitis in immunologically compromised individuals, but is geographically restricted to the sub-Sonoran desert zone of the U.S. (San Joaquin valley fever). *Filamentous molds ar ethe transmission forms of several of the fungal agents (eg, Coccidioides, Blastomyces, Paracoccidiodes) but Cryptococcus does not have a filamentous form. *Septate hyphae with microconidia and macroconidia are the tramsmission (environmental) forms of Histoplasma capsulatum, which is NOT an encapsulated yeast in spite of its name. It is primarily a pulmonary infection acquired by exposure to the droppings of birds or bats.
(SYSTEM: MICROBIOLOGY, NERVOUS); A 42-year-old heart transplant patient complains to her primary care physician about headache and nausea 14 months after transplant. A CT scan of the head shows ring-enhancing lesions. Bacterial, fungal, and viral cultures of the lesions are negative. A biopsy is performed, and a hematoxylin-eosin stain of the biopsied tissue reveals multiple cyst-like structures. How did the infection most likely arise?
Reactivation of latent infection
This patient is most likely infected with Toxoplasma gondii, which is the most common parasitic infection in the United States, and probably also the world. In the U.S., 60-70% of the population are infected, and once acquired, typically in childhood, the parasites persist for the lifetime of the host. The persistent cysts provoke no symptoms in a normal individual, but in the immunologically depressed (for cancer chemotherapy, transplant, or AIDS), will reinitiate proliferation and cause symptoms consistent with those described here. Because of the age of this patient, and her obvious immunosuppression, this is most likely to b3e a reactivated infection, dormant since childhood. *Although an infectedc whole blood transfusion is a possibility, it is a remote one. Toxoplasma is an intracellular parasite, and can only live in nucleated cells, not red blood cells, so it is unlikely to be transmitted during a normal infusion of packed red blood cells. *Ingestion of cyts in pork is incorrect, because althgou it is the most common means of infection of U.S., residents it is NOT likely in this age group, because most primary infections begin in childhood. In addition, the symptoms in this patient are not consistent with a primary infection, which is most likely to be characerized by generalized lymphadenopathy and low grade fever. *MY INCORRECT ANSWER: Although ingestion of oocysts from cat feces is a potential means of infection, it is NOT the most common in the US, or in this particular patient population. *Transplant of an infected organ is NOT the most likely means of infection. Again, bhecause this would be a primary introduction of the parasite, the symptoms the patient would present withou would be those of genralized lymphadenopathy and low-grade fever, NOT the obvious signs of chronic brain infection , as described in this case.
(SYSTEM: IMMUNOLOGY, GENERAL PRINCIPLES). A 32-year-old medical technician had a history of acute eczematous dermatitis on her hands and wrist in the distribution of the latex gloves she wore. The skin of her hands was dry, crusted, and thickened. The eczematous reaction cleared after a 2-week vacation. After 72 hours back on the job, the eczematous dermatitis returned and continued to grow worse. Which of the following characterizes the technician's reaction to the latex gloves?
Type IV reaction
Sensitization to latex has become a major healthcare problem. Local skin irritations are common but more severe allergic reactions occur, up to and including rare anaphylactic reactions that are occasionally fata. The immune responses to latex are immediate-type hypersensitivity (type I) reactions, expressing themselvbes in minutes, and or/or delayed-type hypersensitivity (type IV) reactions, which will express themselves in 48-72 hours. The type I reactions are due to the IgE-mediated sensitivity to latex proteins, while the type IV reactions are due to a cell-mediated response to the chemicals that are added in the pocessing of latex. The type IV response in this circumstance would be referred to as contact dermatitis. *MY INCORRECT ANSWER: Irritant dermatitis can be observed in the early stages of sensitization and can be due to sweating, rubbin, and residual soap. The timing of the reaction after 72 hours points to the type IV reaction rather than an irritant dermatitis. *A type I reaction would have been apparent in minutes, with characteristic rhinitis, conjunctivitis, urticaria, asthma, angioedema, or anaphylaxis after she put on her latex gloves. *A type II reaction is a cytolytic response mediated by an antibody. The type II reaction is observed in the contex of hemolytic anemias, thrombocytopenia, neutropenia, etc. *A type III reaction is an immune-complex response that sets into motion an inflammatory response.
(SYSTEM: IMMUNOLOGY, GENERAL PRINCIPLES); A 15-year-old boy is evaluated by a pediatrician because of a history of multiple bacterial pneumonias. The boy had been apparently normal up until about age 12. In the last three years, he had had five episodes of bacterial pneumonia that were severe enough to require hospitalization. Chest x-ray films taken during the present evaluation demonstrates moderately severe bronchiectasis. A pilocarpine-induced sweat test is negative. T and B cell counts from peripheral blood are normal. Delayed hypersensitivity skin testing shows reactivity to Candida. Immunoglobulin studies demonstrate the following: (IgG below normal; IgA below normal; IgE below normal; IgM below normal). Which of the following is the most likely diagnosis?
Common variable immunodeficiency
This is common variable immunodeficiency. This condition is actually a heterogenous complex of (usually acquired rather than congenital) diseases of differing etiology that share a similar clinical profile. This clinical profile is characterized by the onset of recurrent bacterial infections secondary to markedly decreassed antibody levels, and typically becomes clinically evident in the second or third decade of life. An important distinguishing features from X-linked agammaglobulinemia is that the number of B cells is normal. Some patients have intact cellular immunity, while others have variably severe T cell defects. Other autoimmune conditions (notably Addison's disease, thyroiditis, and rheumatoid arthritis) are common in these patients and their relatives. GI symptoms related to nodular lymphoid hyperplasia in the GI tract may be seen. Other features that may develop include bronchiectasis, carcinoma, and lymphoma. *MY INCORRECT ANSWER: Adenosine deaminase deficiency presents in babyhood with severe combined immunodeficiency. *DiGeorge syndrome usually presents in infancy with hypocalcemia. *Hyper IgM immunodeficiency is due to a failure to convert IgM-producing B cells to production of IgA, IgA, and IgE, leading to high IgM and low values for other immunoglobulins. *X-linked immunoldeficiency differs clinically from common varialbe immunodeficiency by the presence of lower-than-normal B cell levels
(SYSTEM: IMMUNOLOGY, GENERAL PRINCIPLES); A trauma victim in the emergency department requires a transfusion immediately. Type and cross-match tests reveal the following: (NO AGGLUTINATION WITH "PATIENT'S RBC PLUS SERUM FROM AB PERSON" and "Patient's serum plus [type A, B, AB, O, and RhD] RBC). What type of blood should the physician order for him?
AB, RhD+
The patient is AB, Rh+. Persons with this blood type will not possess isohemagglutinins in their bloodstream against either A or B antigens. Their RBC will agglutinate in the presence of sera from individuals with type A, type B or type O blood. The Rh factor is either present (+) or absent (-) from red cells. Since the patient's cells agglutinated in the presence of anti-Rh serum, it is clear that the patient is RhD+.
(SYSTEM: MICROBIOLOGY, RESPIRATORY); A 54-year-old farmer in rural Pennsylvania presents to his physician with chronic cough. Chest x-ray demonstrates a mass lesion with hilar lymphadenopathy. Biopsy of the mass demonstrates multiple, tiny yeast forms within macrophages. Which of the following is the most likely diagnosis?
Histoplasmosis is caused by Histoplasma capsulatum, a dimorphic fungus that grows as a mold in the wild, but as a tiny yeast inside macrophages in humans. The disease is typically asymptomatic or mild enough to go undetected, but when symptomatic, it presents with cough, fever, and malaise. *MY INCORRECT ANSWER: Blastomycosis is characterized by a larger, round-budding yeast form, seen free in the tissues. *Coccidioomycosis is seen mainly in the desert parts of the Southwest U.S. In the lungs, spherules containing endospores are seen. *Paracoccidiodomycosis is endemic in Latin America, especially in Brazil. The infected cells show a typical "pilot's wheel" appearance due to multiple yeasts sprouting out of a single parent cell. *Sporotrichosis most often produces a localized cutaneous infection, following inoculation occuring in association with minor skin trauma during gardening.
(SYSTEM: IMMUNOLOGY, GENERAL PRINCIPLES); A 3-year-old male who is small for his age presents with a history of pyogenic infections. Physical examination is remarkable for a high fever, hepatosplenomegaly, and inguinal and cervical lymphadenopathy. A culture of a purulent discharge from an abscess grows out Staphylococcus aureus. Immunoglobulin and complement levels are normal. The boy received all of the standard immunizations without any adverse effects. The boy's immune deficiency most likely involves which of the following?
phagocytic cells
This patient has chronic granulomatous disease (CGD), which is associated with a defective intracellular respiratory burst in phagocytes. CGD consists of a group of heterogenous disorders of oxidative metabolism affecting the pathways required for hydrogen peroxide production by phagocytic cells. It is inherited as an X-linked or autosomal receissve trait. Normally, stimulated phagocytic cells undergo a respiratory burst consisting of increased oxygen consumption leading to the generation of intracellular hydrogen peroxide and superoxide radicals. They hydrogen peroxide and superoxide radicals are required for the killing of ingested intracellular organisms. The reaction is catalyzed by an NADPH oxidase that appears to be due to inherited mutations in the genes encoding cytochrome suunits. In CGD patients, the engulfment process by the phagocytic cells is normal; however, the pathogenic organism will not be killed, but will persist within the cell. The patients suffer from infections with organisms that are normally considered of low virul3ence (e.g., Staphylococcus aureus, Aspergillus, Candida, Escherichia coli, and Serratia marcescens). The nitroblue tetrazolium (NBT) test is used to screen for CGD. *B cells are responsible for antibody-mediated immunity, and the immunoglobulin levels in this patient were normal. *MY INCORRECT ANSWER: Chemotaxis is important in the migration of the phagocytic cell toward the site of infection, not in intracellular killing. *IgG subclass 2 is the most important immunoglobulin in the protection against encapuslated organisms. *T cells are important in the host response to viruses, fungi, and intracellular bacterial organisms. The patient was immunized normally (including the live, attentuated MMR vaccine), making T cell dysfunction unlikely.