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24 Cards in this Set

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Correct Answer
Explanation (Hint):
A 38-year-old primigravid woman in her second trimester of pregnancy complains to her obstetrician of urinary frequency and burning. A clean catch specimen of urine is obtained and submitted to the laboratory for culture, Gram's stain, and biochemical analysis. Urease-positive gram-negative bacilli with smarming motility are detected. Where is the proton-motive force that generates energy for flagella located in this organism?
Cytoplasmic membrane
Unlike eukaryotic cells in which the elctron transport system is located on mitochondria, the electron transport system of bacteria is located on the cytoplasmic (plasma) membrane. Since prokaryotes possess no internal membrane-bound organelles, all biochemical processes that require membrane support must occur on the internal surface of the cytoplasmic membrane. *Mesosomes are complex invaginations of bacterial cell membranes that serve in cell division. *MY INCORRECT ANSWER: Bacteria do NOT have mitochondria or nuclear membranes. *Polyribosomes function in bacterial protein synthesis.
An autopsy is performed on a man who suddenly began vomiting voluminous quantitis of blood and exanguinated. The man's stomach is presnted in the accompanying photograph. Which of the following organisms is most likely implicated in the pathogenesis of this disease?
Helicobacter pylori
The gross photograph shows a stomach with a perforated peptic ulcer. Perforation of a peptic ulcer is potentially fatal, because of either peritonitis with sepsis or sudden exanguination (if the perforation damages one of the many arteries of the stomach). Peptic ulcer disease, gastritis, and possibly gastric carcinoma and gastric lymphoma have been strongly associated with Helicobhacteri pylori colonization of the mucus layer covering the gastric mucosa. Colonization is associated with destruction of the mucus layer, thereby destroying its protective function. *Cryptosporidium parvum causes diarrhea that is severe in immunocompromised patients. *Entamoeba histolytica produces dysentery-like symptoms or can cause liver abscess. *MY INCORRECT ANSWER: E. coli cuases a variety of diarrheal disease and can infect the bladder and soft tissues. *Mycobacterium tuberculosis causes tuberculosis, characterized by granuloma formation, especially in the lungs.
A new vaccine developed by the military protects recruits against respiratory infections causes by adenovirus serotypes 4 and 7. The virus, which is living and non-attenuated, is delivered in an enteric coated capsule. It establishes an asymptomatic intestinal infection, which stimulations production of memory cells that disseminate throughout the body to protect all the mucosal surfaces from subseuqnt respiratory attack. Which of the following cytokines produced as a result of this vaccination is most likely to induce a protective response?
The most important protective immune response against mucosal surface pathogens such as the respiratory adenoviruses is an IgA antibody response that would inhibit the binding of virions to the respiratory mucosa. This response is mediated by TH2 cells and their cytokines, which stimulated isotype switching in B lymphocytes to IgA production. The cytokine that has shown the strongest association with the swithc to IgA is interleukin-5. *Interferon-gamma is a product of TH1 cells that stimulates the cells of the cell-mediated immune response. Although the cell-mediated response is important in eradicating virus-infected cells from the body, immunity to reinfection is mediated by IgA. *MY INCORRECT ANSWER: Interleukin-2 is a product of TH cells that induces proliferation of other lymphocytes. It is important in the cloning of antigen-specific cells during both cell-mediated and humoral immune responses, but does not mediate IgA production specifically. *Interleukin-4 is a product of TH2 cells associated with stimulation of the isotype swithc of B cells to make IgE. It would not be a protective anti-virus response, although this cytokine could encourage protection against helminths. *Interleukin-6 is an endogenous pyrogen that is produced by TH0 and TH2 cells. It is important in encouraging the differentiation of antigen-specific B cells, but is NOT known to be associated with IgA production.
A 73-year-old woman with a history of diabetes presents with left ear pain and drainage of pus from the ear canal. She has swelling and tenderness over the left mastoid bone. Which of the following microorganisms is the most likely causative agent?
Pseudomonas aeruginosa
Pseudomonas aeruginosa causes malignant otitis externa, which is a severe necrotizing infection of the external ear canal. Infection tends to spread to the mastoid bone, temporal bone, sigmoid sinus, base of the skull, meninges, and brain. Patients at increased risk include the elderly, those with diabetes, and the immunocompromised. Psuedomonas is also assicated with many other clinical syndromes, including infection following traumatic wounds to the feet in persons wearing sneakers or rubber-soled shoes, since the organism can be cultured from the shoes. *Hemophilus influenza produces a variety of clinical syndromes. Haemophilus influenzae is the 3rd most common cause of meningitis in children aged 1 month to 18 years. It is the most common cause of acute epiglotitis, the most common cause of purulent bacterial conjunctivitis, and the second-most common cause of otitis media. Patients at risk include those with COPD and cystic fibrosis, alcoholics, splenectomized patients, and young patients. *Klebsiella pneumoniae is a gram-negative organism that produces a necrotizing pneumonia in diabetics and alcoholics. Patients typically present with an abrupt onset of fever, shaking chills, and purulent, foul-smelling sputum. *MY INCORRECT ANSWER: Mucor is a fungal infection that is particularly severe in the diabetis or the immunocompromixed patient. IN the acidotic diabetic, the fungus produces a life-threatening, invassive rhinocerebral infection. The infection beings in the nasal passages, extends into the paranasal sinuses, and spreads through the cribiform plate to the frontal lobes of the brain. Patients typically complain of headache, facial pain, and orbital swelling. *Streptococcus pyogenes causes bacterial pharyngitis, otitis media, and sinusitis. It is also associated with toxin-related diseases and skin infections.
A 7-year-old girl develops behavioral changes, and her performance in school begins to deteriorate. Several months later, she develops a seizure disorder, ataxia, and focal neurologic symptoms. She is eventually quadriparetic, spastic, and unresponsive. Death occurs within a year. This patient may have had which of the following viral diseases at 1 year of age?
The child has subacute sclerosing panencephalitis (SSPE), which is fortunately a very rare, late complication of measles infection at an early age. The existence of this complication is part of the rationale to immunize children to measles at an early age. It is thought that very young children's immune and neurologic systems may permit the virus to become established in the brain. The exact mechanism of injury is poorly understood, but the brain shows encephalitis involving both gray and white matter. 40% of cases die within 1 year, and it is thought that the disease is probably always eventually fatal. None of the other diseases progresses to SSPE.
A 36-year-old farmer has been exposed to poison ivy on several different occasions and usually develops severe skin lesions. He enrolls in an immunological study at an urban medical center. A flow cytometric measurement of T cells rev3eals values within the normal range. An increased serum concentration of which of the following cytokines would decrease the likelihood of a delayed-type hypersensitivity reaction in this individual?
The IL-10 cytokine is produced by T helper 2 (TH2) cells and inhibits T helper 1 (TH1) cells. Since the cytokines from TH1 cells stimulate cell-mediate immunity and delayed hypersensitivity, an increased level of IL-10 would decrease the likelihood of a delayed type hypersensitivity reaction. Other cytokines from TH2 cells stimulate B cells to produce antibody. *The gamma interferon cytokine from T help1 cells inhibits TH2 cells. It also activates NK cells and activates macrophages. *MY INCORRECT ANSWER: IL-2 stimulates the TH1 subset, CD8 T cytotoxic cells, and activates NK cells. It is one of the most active cytokines and is involved in many other reactions. *IL-5 is secreted by TH2 cells and promotes B-cell proliferation, IgA synthesis, and eosinophil proliferation. It does not have a direct effect on TH1 function. *The IL-8 cytokine is produced by macrophages and is chemotactic for neutrophils. This cytokine is most important in stimulating an inflammatory reaction and attraction of neutrophils to the site.
An 8-year-old boy is brought to the emergency room with a 3-day history of fever of 102 degrees F and abdominal pain. He also complains of pain in hbis right knee and right elbow. He was seen four weeks ago because of a sore throat and a rash. A throat culture performed at that time grew gram-positive cocci in chains. Amoxicillin was prescribed, but the boy's mother did not fill the prescription. ON physical examination, his temp is 38.7 C (101.7 F), HR is 96, and BP is 100/60. Cardiac examination reveals a pansystolic blowing murmur heard best at the apex. His right elbow is tender on extension and flexion with mild swelling. Laboratory tests reveal a positive C-reactive protein, an ESR of 40 mm/h, and a WBC count of 22,000/mm3 with a left shift. ECG shows a prolonged PR interval. Which of the following tests would be positiv efor the microorganism responsible for this patient's illness?
sensitivity to bacitracin
This case is class for Rheumatic fever, including two of the major Jones jcriteria (carditis, polyarthritis) and several minor criteria (fever, arthralgia, elevated ESR, leukocytosis, C-reactive protein, prolonged PR interval). Rheumatic fever is a sequela of untreated infection with Group A Streptococcus (S. pyogenes). S pyogenes is differentiated from the other beta-hemolytic Strep by its sensitivity to the antibiotic bacitracin. *The catalase test is used to differentiate Staphylococci from Streptococci. Staphylococci are catalase positive, Streptococci are catalase negative. So, S. pyogenes would be catalase negative. *The coagulase test is used to differentiate Staph aureus from the other Staph spp. Staph aureus is coagulase positive; the others are negative. *Sensitivity to novobiocin is used to differentiate Staph saprophyticus (resistant) from Staph epiderrmidis (sensitive). *MY INCORRECT ANSWER: Sensitivity to optochin is used to differentiate Strep pneumoniae (sensitive) from viridans Strep (resistant).
A traveler to a foreign country develops acute lymphatic filariasis four months after his return to the United States. His symptoms include scrotal inflammation, itching, and localized scrotal swelling and tenderness of the inguinal lymph nodes. Which of the following immune mechanisms does the body employ against the live filarial worms?
Antibody-dependent cell-mediated cytoxocitiy
Filarial parasites have a complex life cycle beginning with transmission by mosquitoes or other arthropods. The offspring of adults (microfiliariae) either circulate in the blood or migrate through the skin, often inhabiting lymphatics. Microfilariae are ingested by the arthropod vector and develop over 1 to 2 weeks into new infective larvae. The adult worms elicit an inflammatory reaction in the lymphatics, eventually leading to lymphatic obstruction and edema. The body reacts to large tissue parasites, such as filarial worms, by coating them with a thin layer of IgE molecules, which trigger eosinophil-mediated cytotoxicity (a form of Type II hypersensitivity) and release of vasoactive and spasmogenic substances from mast cells and basophils (local anaphylaxis, a form of Type I hypersensitivity). *Other forms of Type II hypersensitivity include complement-mediate reactions (e.g., the lysis of blood cells seen in transfusion reactions) and *MY INCORRECT ANSWER*: anti-receptor antibodies (e.g., muscle weakness in myasthenia gravis). *Type III hypersensitivities usually take the form of vasculitis secondary to deposition of circulating antigen-antibody complexes; the Arthus reaction is a specific variant of these reactions in which local vasculitis induces tissue necrosis, often in the skin.
A Malaysian famiy is referred to a specialist in Memphis, Tennessee for evaluation of a possible genetic immunologic defect. 4 of 6 of the members of this family have displayed increased susceptibility to extracellular bacteria and elevated serum levels of IgM and IgG. Analysis of serum complement protein levels reveals near absence of component C4. This deficiency would inhibit whihc of the following complement activities?
Completion of the classic pathway to the splitting of C3
The classic complement pathway involves C1, C4, and C2 to the point of splitting C3. C3 is then split to yield C3b and C3a. A deficiency of C4 would have no effect on any of the other answer choices listed. *The complement protein C3 can be split into C3a and C3b using the alternative pathway. The additional proteins required in this pathway would be factors B and D and properdin. *MY INCORRECT ANSWER: The C5 convertase enzyme can be formed in the alternative pathway without using C4. *The C5 molecule would be split into C5a and C5b using the alternative pathway, without the involvement of C4. *The membrane attack complex (C5b, C6, C7, C8, and polymers of C9) lyses the pathogenic c ell. This process does not require the altnerative pathway and would not require C4.
A 15-year-old boy presents to his physician with several weeks of slowly worsening pruritis of both of his feet. He is otherwise well and taking no medications. On examination, he has bilateral, erythematous, dry scaling lesions that are most obvious in the interdigital web spaces and on the soles. There is no bleeding or exudate. What would most likely be found in a potassium hydroxide (KOH) mount of a scraping of the affected skin?
Branching, septate hyphae with arthroconidia
This is a case of tinea pedis, or athlete's foot, caused by a variety of dermatophytic fungi, which are easily detected on alkali mounts of scraped skin as colorless, branching hyphae with cross-walls and arthroconidia. *Hyphae with rosettes of conidia describes the environmental/transmission form of Sporothrix schenckii, the agent of rose gardener's diseasse, which is a subcutaneous mycosis. *Budding yeasts describes the form found in clinical specimens from patients with sporotrichosis. *Hyphae, arthroconidia, and blastoconidia would be found in clinical specimens from patients infected with Trichosporon beigelii (white piedra), which is a superficial mycosis of the hair of the head. *Pigmented, septate hyphal fragments would be found in cases of phaeohyphomycosis, a diverse group of cyst-forming subcutaneous, pigmented (dematiaceous) fungi, rare in the U.S. *MY INCORRECT ANSWER: Short, curved hyphae and round yeasts, or the "spaghetti and meatball" presentation in clinical specimens, are characteristic of Malassezia furfur, the agent of pityriasis versicolor.
A 12-year-old girl presents with a skin abscess. The causative organism is found to be Staphylococcus aureus. Over the past year, she has had several similar abscesses, as well as two bouts of aspergillosis. Which of the following is the most likely explanation for her repeated infections?
Defective NAPDH oxidase
A history of recurrent infection with S. aureus and Aspergillus spp. Suggests a diagnosis of chronic grnulomatous disease, which is aused by a defect in the NADPH oxidase of neutrophils, resulting in an inability to generate toxic oxygen metabolites following phagocytosis. Patients become susceptible to certain opportunistic infections, particularly those caused by S. aureus, Aspergillus spp., Nocardia, and Salmonella. *Defective chemotactic response, seen in diseases such as Chediak-Higashi syndrome and lazy-keukocyte syndrome, would make patients more susceptible to infections by bacteria such as staphylocci and streptococci. *Deficiency of C5, a complement component, would make patients prone to infection by a gram-negative bacteria, especially Nesseria species. *MY INCORRECT ANSWER: IgA deficiency represents the most common immunodeficiency and would present with increased predisposition to autoimmune disorders, respiratory infections, and milk allergy. *Thymic hypoplasia is caused by defective development of the 3rd and 4th pharyngeal pouches. The result is decreassed T-cell levels, making patients more prone to viral and fungal infections. They also will exhibit hypocalcemia and othe rsigns of parathyroid insufficiency.
A 38-year-old woman with SLE is seen by her family physician. On her last visit, he sent blood to the laboratory for an antinuclear antibody panel. Based on the results, he recommends that the patient by seen by a nephrologist. A high titer of autoantibodies directed against which of the following antigens most likely prompted his decision?
Double-stranded DNA (dsDNA)
Antibodies to double-stranded DNA, unlike most other autoantibodies, are considered to have prognostic significance in SLE. High titers of this antibody are associated with the development or progression of lupus nephritis. Lupus nephritis can occur in the absence of any demonstrabale abnormalities on urinalysis; renal biopsy is helpful in such cases to document disease progression. *Anti-histone antibodies can be seen as one of several autoantibodies in SLE or as an isolated finding in drug-induced lupus. *High titers of anti-RNP specifically suggests mixed connective tissue disease rather than lupus, although 30-40% of lupus patients will have this antibody. *MY INCORRECT ANSWER: Anti-Sm is specific for SLE, but does not predict outcome. *Anti-ssDNA autoantibodies are a nonspecific feature of SLE and can be seen in other autoimmune diseases.
A small 9-month-old male with a history of recurrent pyogenic infections is seen in a clinic. Immunoglobulin levels and a CBC are performed. The CBC is normal except for slight neutropenia and thrombocytopenia. Determination of immunoglobulin levels indicates elevated IgM, but deficiencies of IgG and IgA. The underlying defect involves whihc of the following molecules?
CD40 ligand (CD40L) on the T cell
The correct answer is A. Patients with hyper-IgM syndrome (HIGM) experience very little, if any, isotype swithing. The B cells in these patients cannot undergo the switch from IgM to IgG, IgA, or IgE that normally occurs during B-cell maturation. When B cells undergo isotype switching, they require two factors: IL-4, which binds to a specific receptor on the B cells, and the CD40 molecule on the B-cell surface, which binds to the CD40 ligand (CD40L) on an activated-T cell surface. The deficien cy is due to mutations in the CD40L. This immunodeficiency results in patients who are IgG- and IgA-deficient, but synthesize large amounts of polyclonal IgM. Affected individuals are susceptibe to pyogenic infections, and often form IgM autoantibodies to neutrophils, platelets, or tissue antigens. The disease is inherited as X-linked recessive in 70% of cases. *The problem is due to mutations in the CD40L, but not the CD40 molecule on the B cell. *Gamma interferon is primarily a type I helpter T cell (TH1) cytokine, although it does inhibit the TH2 lineage response to specific antigens. *MY INCORRECT ANSWER: A decrease in IL-2 would inhibit the cell-mediated immune response and the patient would be susceptibe to infection with intracellular microorganisms. *IL-3 is considered a growth factor for hematopoietic stem cells and mast cells. The patient had a normal CBC except for slight neutropenia and thrombocytopenia.
A 21-year-old college student from Connecticut with a past history of Lyme disease presents with chronic pain and swelling in his right knee. He states that he has had problems with the knee for the past two years. Which of the following HLA alleles would you expect to be present in this individual?
Approximately 60% of patients in the United States who contract Lyme disease, but are not treated with antibiotics, will develop frank arthritis. The pattern typically consists of intermittent attacks of oligoarticular arthritis in large joints (especially knees) lasting for weeks to months in a givent joint. Patients with persistent arthritis have a higher frequency of HLA-DR4 Class II MHC complex than patients with brief LYme arthritis or normal controls. *HLA-B9, and HLA-B17 are not thought to be associated with Lyme disease arthritis. *HLA-DR3 is associated with a variety of disorders, but not Lyme disease arthritis. *MY INCORRECT ANSWER: HLA-B27, although associated with reactive arthritis, is not associated with Lme disease arthritis.
A 33-year-old woman presents with fever, vomiting, severe irritative voiding symptoms, and pronounced costovertebral angle tenderness. Laboratory evaulation reveals leukocytosis with a left shift; blood cultures indicate bacteremia. Urinalysis shows pyuria, mild hematuria, and gram-negative bacteria. Which of the following drugs would best treat this patient's infection?
Ampicillin and gentamicin
Acute pyelonephritis is an infectious diseasse involving the kidney parenchyma and the renal pelvis. Gram-negative bacteria, such as Eschericihia coli, Proteus, Klebsiella, and enterobacter, are the most common causative organisms in acute pyelonephritis. Laboratory evaluation will often reveal leukocytosis with a left shift, and urinalysis typically shows pyuria, varying degrees of hematuria, and white cell casts. Since bactermia is present, the patient should be hospitalized and empirically started on IV ampicillin and gentamicin. This regimen may need to be changed, however, once the sensitivity results are available. *MY INCORRECT ANSWER: Erythromycin and tetracycline are both bacteriostatic antibiotics and would not be recommended in a patient with a severe infection, such as acute pyelonephritis with bactermia. *Vancomycin is primarily used in the treatment of severe gram-positive infections. *Phenazopyridine is a urinary analgesis, and nitrofurantoin is a urinary tract anti-infective. Although nitrofurantoin is indicated for the treatment of "mild" cases of pyelonephritis, as well as cystitis, this patient's condition is severe and should be treated with appropriate antibiotics.
A 44-year-old white female presents with severe Raynaud's phenomenon, dysphagia, and sclerodactyly, and facial and palmar telangiectasis. Which of the following autoantibodies is most likely to be present in this patient?
Anti-centromere antibody
The symptoms described in the question are classic for CREST syndrome. CREST syndrome is the combination of calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia. Anti-centromere antibodies are reported in a high percentage of patients with CREST, but in a small percentage of pure scleroderma patients. *Anti-histone antibody is a marker for drug-induced lupus erythematosus. *MY INCORRECT ANSWER: Anti-SS-A is a marker for Sjogren's syndrome, characterized by dry eyes and dry mouth. *Anti-SS-B is an autoantibody directed against ribonucleoproteins, and is a marker for Sjogren's syndrome. *Rheumatoid factor is generally an IgM autoantibody directed against the Fc portion of IgG. RF is positive in 80% of patients with rheumatoid arthritis and may also be found in low titers in patients with chronic infections, other autoimmune diseases such as SLE, and Sjogren's syndrome, or chronic pulmonary, hepatic, or renal diseases.
A 6-year-old boy presents with a rash that started as a superficial accumulation of several small vesicles on his legs below the knees. He is afebrile and appears normal, other than these lesions. The child lives in the suburbs and often plays outside in the local woods in short pants. The lesions are honey-brown and crusted, with an erythematous base, and are in various stages of crusting and openness. What is the most important laboratory test to distinguish between the genera of potential causative agents for this condition?
Catalase test
This is a likely case of Streptococcus pyogenes impetigo because of the description of honey-crusted lesions; but the other major cause of impetigo is Staphylococcus aureus, and these two genera are distinguished on the basis of the catalase test. *CAMP test is the test used to distinguish the Group B streptococci from other streptococci, and would not be useful here. *The coagulase test is the test used to distinguish Staphylococcus aureus from all other staphylococci, and would not distinguish between the genera of agents causing impetigo. *The ELEK test is the immunodiffusion test used to identify toxin-producing strains of Cornyebacterium diptheriae.. *MY INCORRECT ANSWER: Gram's stain would not be useful, as both of the most common agents of impetigo are gram-positive cocci. *The oxidase test is the test used to identify Neisseria and would not be useful here.
A research laboratory is studying mechanisms of immunity to Babesia microti in mice. Cells from immune mice are separated by flow cytometry, using fluorescently labeled anibodies directed against a variety of cell surface markers. Infected red blood cells are then added to the separated populations of immune cells and observed for lysis in the absence of complement. Which of the following cell surface markers would be most useful in identifying a cell capable of lysing infected cells in this system?
Babesia microti is an intraerythrocytic parasite that causes a mild anemia and fever in affected humans. It is transmitted by the same tick that transmits Lyme disease, Ixodes scapularis. Red blood cells are the only cells in the body that are devoid of MHC class I molecules, so the lysis of thse cells by a cytotoxic cell would only be possible using NK cells. NK cells are the cytotoxic cell that kills in the absence of MHC class I recognition. NK cells are actively inhibited if they recognize these antigens on a target cell. The most specific marker for the identification of NK cells is CD56, although CD16 is also found on their surface. *CD4 cells are helper T cells. They assist in both antibody-mediated and cell-mediated immune responses, but by themselves, as stipulated in this question stem, they would not be capable of lysis of red blood cells. *MY INCORRECT ANSWER: CD8 cells are cytotoxic T cells. These cells kill by identifying alterations in the MHC class I molecule. Since such molecules are absent from erythrocytes, cytotoxic T c ells are NOT capable of lysing erythrocytes. *CD14 is the endotoxin receptor that is found on macrophages. Macrophages are capable of ingesting and destroying infectected erythrocytes in the spleen, but are not capable of causing their lysis in this system. *CD16 is the receptor for the Fc component of immunoglobulin G. It is present on a variety of cells, including natural killers, macrophages, and neutrophils. Therefore, it is not the best marker for the NK cell uniquely, but would label several populations of cells.
Which of the following is more frequently associated with Klebsiella pneumoniae than with Pseudomonas aeruginosa?
upper lobe cavitation
Klebsiella pneumoniae is a well-recognized cause of community-acquired lobar pneumonia associated with cavitation. It is found typically in alcoholic males over 40 years of age with underlying diabetes or obstructive lung disease. Klebsiella pneumoniae mimics Streptococcus pneumoniae as a pulmonary pathogen, except that Klebsiella has a greater tendency to progress to lung abscess and empyema. Pseudomonas aeruginosa is usually associated with patients on ventilators, parciularly in intensive care units. Immunocompetent patients usually have bilateral bronchopneumonia without cavitary lesions. *Artificial ventilation is calssically associated with Pseudomonas aeruginosa infection. The organism thrives in a wet environment, such as respirators, cleaning solutions, disinfectants, sinks, vegetables, flowers, endoscopes, and physiotherapy pools. *P. aeruginosa is a very important pathogen. Mucoid strains of this organism infect the airways in pateints with cystic fibrosis, leading to acute exacerbations and chronic progression of lung damage. *Both organisms cause disease in association with diabetes. Klebsiella pneumonia produces pulmonary disease and P. aeruginosa causes necrotic skin ulcers in diabetics. *MY INCORRECT ANSWER: Green-colored sputum is associated with Pseudomonas aeruginosa, since more than half of the clincal isolates produce the blue-green pigment pyocyanin, which is helpful in identifying the organism.
A 46-year-old woman presents with complaints of feeling as if she has "sand in her eyes" and reports difficulty swallowing such foods as crackers or toast. A biopsy of an enlarged salivary gland reveals lymphocytic infiltration. There is hperplasia of the ductal linings and signs of fibrosis and hyalinization of the acini. Which of the following pairs of tests would likely yield positive results in this patient?
Rheumatoid factor and anti-SS-A antibody
This patient has Sjogren syndrome, which is an autoimmune disease characterized by lymphocytic infiltration of exocrine glands, resulting in dry mouth (xerostomia) and dry eyes (keratoconjunctivitis sicca). Patients have an increased risk of malignant lymphoma. Autoantibodies produced include anti-Ro (SS-A), anti-La (SS-B), antinuclear antibodies, and rheumatoid factor. *Anti-centromere antibodies are a very specific marker for CREST syndrome. Rheumatoid factor (IgM antibodies against one's own IgG) is usually positive in rheumatoid arthritis but may be seen in low titers in patients with other autoimmune diseases and chronic inflammatory conditions. *Anti-Scl-70 antibodies are seen in patients with scleroderma. Anti-Smith antibody is seen in SLE. *MY INCORRECT ANSWER: Anti-Smith antibody and anti-double stranded DNA antibody are associated with SLE. *Rheumatoid factor is seen in approximately 80% of patients with rheumatoid arthrits and in low titers in other autoimmune disorders. Anti-double stranded DNA (anti-dsDNA) is seen in patients with SLE.
A 26-year-old obstetric patient becomes acutely ill during her first trimester with infectious mononucleosis-like symptms, but her heterophil antibody test was negative. A careful history reveals that the family has two cats in the house. The approprate laboratory tests indicate the expectant mother is infected with Toxoplasma gondii. Months later, the woman delivers a full-term baby with no obvious signs of infection with the protozoan parasite. The best test to diagnose acute infection in the neonate would be a parasite-specific ELISA for which isotype of immunoglobulin?
IgM immunoglobulin directed against Toxoplasma would provide evidence of infection in the newborn baby. IgM is the only antibody that a baby can form with an acute infection. It is the first antibody that is formed in an infection and it is also the antibody that is present on the surface of immature and mature B cells. *IgA is the antibody that is produced in response to mucosal infections. It cannot cross the placenta. The baby's immune system is still not well developed at birth and cannot produce IgA immunoglobulin. In adults or older children, IgA exists in serum in a monomeric form but is present in seromucuous secretions as a dimer. *MY INCORRECT ANSWER: is the antibody that is produced in response to an allergen. It cannot cross the placenta, and is not present in the baby at birth or for some time after birth. The baby's immune system is still not well developed at birth and can initially only form IgM immunoglobulin. *IgG1 and IgG4 immunoglobulins might be present in the baby, but would not indicate infection in the infant. The presence of these isotypes would indicate that the mother was infected with the organism and produced antibody that was transported across the placenta in utero. IgG is the only immunoglobulin that can cross the placenta, providing protection to the baby during the first few months of life.
An infectious disease specialist in New York City is conducting a study of the effect of cytokine administration on the progression of multiple drug-resistant tuberculosis in HIV-positive patients. A variety of cytokines produced by recombinant DNA are aerosolized and administered twice daily to a group of 20 individuals. Treatment progress is monitored by chest x-ray and sputum culture. Which of the following cytokines is likely to have the most beneficial effect on macrophage intracellular killing of the mycobacteria?
Mycobacterium tuberculosis is an intracellular pathogen that lives inside macrophages. The protective immune response to this organism depends on the stimulation of more efficient intracellular killing in phagocytic cells by the cytokines of TH1 cells. Interferon-gamma is a product of TH1 cells that acts on macrophages to enhance their microbicidal activities. *Interferon-alpha is a product of leukocytes that inhibits viral replication. It is unlikely to have an effect on an intracellular bacterial infection. *Interferon-beta is a product of fibroblasts that inhibits viral replication. It is unlikely to have an effect on an intracellular bacterial infection. *Interleukin-2 is a product of TH cells that causes proliferation (cloning) of other lymphocytes. Since the macrophage is an end cell, incapable of further replication, it would not be affected by IL-2 administration. *MY INCORRECT ANSWER: Tumor necrosis factor-alpha, a product of macrophages and NK cells, is cytotoxic for tumor cells, induces cytokine production and causes the cachexia of chronic inflammation. It is unlikely to have a beneficial result on a bacterial infection of macrophages.
A 39-year-old black man presents with complaints of anorexia, malaise, fatigue, dark urine, and upper abdominal discomfort. He admits to homosexuality, but denies blood transfusions, alcohol intake, or intravenous drug abuse. On physical examination, the patient has a temperature of 100.2 degrees F, scleral icterus, and jaundice. His liver is palpable below the right costal margin, and there is moderate right upper quadrant tenderness. Liver function test results are as follows: total bilirubin 12.4% SGOT 980 units, SGPT 1200 units. Serologic findings are as follows: anti-hepatitis A IgM negative, HBsAg positive, anti-HBc IgM positive, HBeAg positivbe, anti-HBsAb negative, hepatitis C negative. When this patient enters the window period, what would likely be the first change in his serologic findings?
He will become HBsAg negative
This patient has acute hepatitis B. The "window period" refers to that period in infection when neither hepatitis B surface antigen (HBsAg) nor its antibody (HBsAb) can be detected in the serum of the patient. It is an immunologically mediated phenomenon caused by the precipitation of antigen-antibody complexes in their zone of equivalent concentrations and, thereby, their removal from the circulation. Because of this, the first thing that will happen in the window period is that the serum will become negative for the surface antigen (HBsAg), as that antigen is precipitated out of the serum by developing levels of its specific antibody (HBsAb). *MY INCORRECT ANSWER: HBcAg is not typically measured in the serum. *Levels of the c-core antibody HBc IgG and HBeAg do not have a relationship to the window period. *Levels of HBsAb will not be detectable until there is antibody excess, and the patient is leaving the window period.