Imm. Ch1

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effector response

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Action that occurs after recognition and binding of antigen by antibody; lysis by complement proteins is an effector response. Recognition of a pathogen by the immune system triggers an effector response that eliminates or neutralizes the invader.

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memory response

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an attribute of the immune system mediated by memory cells whereby a second encounter with an antigen induces a heightened immune reaction upon later attack.

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What are the two types of immunity?

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1) innate immunity
2) adaptive immunity

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innate immunity

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Nonspecific host defenses that exist prior to exposure to an antigen and involve anatomic, physiologic, endocytic and phagocytic and inflammatory mechansisms.
- includes molecular and cellular mechanisms predeployed before an infection and poised to prevent or eliminate it.
- first line of defense prevents most infections at the outset or eliminates them within hours of encounter
- recognition elements precisely distinguish between self and pathogens, but they are not specialized to distinguish small differences in foreign molecules

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adaptive immunity

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Host defenses that are mediated by B and t cells following exposure to antigen and that exhibit specificity, diversity,memory, and self-nonself recognition.
- develops in response to infection and adapts to recognize, eliminate and then remember the invading pathogen.
- activated after innate immune response
- recognizes pattern of specific strand of bacteria

- is contingent upon innate immunity and begins a few days after the initial infection.
- consequence of adaptive immunity response is memory.

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vaccine

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a preparation of immunogenic material used to induce immunity against pathogenic organisms

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attenuation

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To decrease virulence of a pathogen and render it incapable of causing disease. Many vaccines are attenuated bacteria or viruses that raise protective immunity without causing harmful infection.

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serum

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Fluid portion of blood (plasma), which is free of cells and clotting factors.

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immunoglobulin

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protein family with antibody activity
(prev. gamma gobulin)

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antibodies

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A protein (immunoglobulin) consisting of two identical heavy chains and two identical light chains, that recognize a particular epitope on an antigen and facilitates clearance of that antigen. Membrane-bound antibody is expressed by B cells that have not encountered antigen; secreted antibody is produced by plasma cells. Some antibodies are multiples of the basic four-chain structure.

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active immunity

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adaptive immunity that is induced by natural exposure to a pathogen or by vaccination

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passive immunity

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adaptive immunity conferred by the transfer of immune products such as antibody or sensitized T cells, from an immune individual to a nonimmune one

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phagocytes

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a cell with the capacity to internalize and degrade microbes or particulate antigens; neutrophils and monocytes are the main phagocytes

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humoral immunity

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immunity mediated by antibodies contained in body fluids (including plasma, lymph and tissue fluids)

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cell-mediated immunity

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Host defenses that are mediated by antigen-specific T cells and various nonspecific cells of the immune system. It protects against intracellular bacteria, viruses, and cancer and is responsible for graft rejection. Transfer of primed T cells confers this type of immunity on the recipient.
-Metchnikoff-cells rather than serum components were the major effector of immunity
(likely monocytes and neutrophils)

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lymphocyte

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A mononuclear leukocyte that mediates humoral or cell mediated immunity.

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antigen

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any substance (usually foreign) that binds specifically to an antibody or a T-cell receptor; often is used as a synonym for immunogen

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selective theory

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- cells contained "side-chain" receptors that could react with infectious agents and inactivate them
- the specificity of the receptor was determined in the host before its exposure to the antigen and the antigen selected the appropriate receptor

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instructional theory

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- antigen played a central role in determining the specificity of the antibody molecule
- the antigen served as a template around which the antibody would fold

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clonal-selection theory

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- adapted from selective theory
- an individual lymphocyte expresses membrane receptors that are specific for a distinct antigen.
- determined before lymphocyte is exposed
- binding of antigen to its specific receptor activates the cell causing it to proliferate into a clone of cells that have the same immunologic specificity as the parent cell.

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pathogens

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organisms that cause disease

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pathogenesis

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the means by which pathogens attack their host

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opportunistic infections

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infections by ubiquitious microorganisms often observed in cases of immune deficiency

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endocytosis

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1) the general term for the uptake by a cell of material from its environment
- is an important innate defense mechanism by phagocytosis
2) receptor-mediated endocytosis
3) pinocytosis

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What happens in phagocytosis?

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The cellular uptake of particulate materials by engulfment.
-a cell's plasma membrane expands around the particulate material

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receptor-mediated endocytosis

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extracellular molecules are internalized after binding to specific cellular receptors

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pinocytosis

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the process by which cells take up fluid from the surrounding medium along with any molecules contained in it

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lysozyme

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An enzyme present in tears, saliva, and mucous secretions that digest mucopeptides in bacterial cell walls and thus functions as a nonspecific antibacterial agent. It has frequently been used as a target antigen in immunological studies.-

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interferon

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Several glycoprotein cytokines produced and secreted by lymphocytes that induce an antiviral state in other cells and also help to regulate the immune response.
- a group of proteins produced by virus-infected cells
- has the ability to bind to nearby cells and induce a generalized antiviral state

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complement

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a group of serum membrane proteins that interact with one another and with other molecules of innate and adaptive immunity to carry out key effector functions.
- circulate in an inactive state
- can be converted to an active state with the ability to damage
membranes of pathogenic organisms by specific and nonspecific immunologic mechanisms, either destroying the pathogens or facililitating their clearance.
- would recognize bacteria by their cell wall
- the innate immune system recognizes particular chemical compound /not as specific

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collectins

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Proteins that may kill certain bacteria directly by disrupting their lipid membrane or alternatively, by aggregating the bacteria to enhance their susceptibility to phagocytosis.

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pattern recognition

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The ability of a receptor or ligand to interact with a class of similar molecules, such as mannose-containing oligosaccharides.
- molecules involved in innate immunity
- recognize a given class of molecules
- may be soluable (lysozyme)
- may be cell-associated receptors (Toll like receptors TLRs)

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cytokines

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Any of numerous secreted, low-molecular weight proteins that regulate the intensity and duration of the immune response by exerting a variety of effects on lymphocytes and other immune cells.

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chemokines

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Any of several secreted low-molecular weight polypeptides that mediate chemotaxis for different leukocyte and regulate the expression and/or adhesiveness of leukocyte integrins.
A restricted class of cytokines that have chemotactic activity and recruit specific cells to the site of the cell secreting that cytokine.

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signaling

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Intracellular communication initiated by receptor-ligand interaction.
-mediated by cytokines
- reaction between a ligand and a cell membrane-bound molecule (receptor) or between membrane-bound molecules on two different cells

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signal transduction begins when

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-when a signal binds to its receptor
-may be inside or outside the cell
-if unable to penetrate the membrane, they bind to receptors on the cell surface
-includes water soluble signalling molecules and membrane-bound ligands
-hydrophobic signals (steroids) can diffuse through the cell membrane and are bound by intracellular receptors

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many signal transduction pathways involve the signal-induced assembly of pathway components

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-adaptor proteins bind specifically and spontaneously to two or more different molecules with roles in the signaling pathway, bringing them together and promoting their combined activity

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What are the common themes typical of signal transduction pathways?

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1) signal transduction begins when a signal binds to its receptor

2) many signal transduction pathways involve the signal induced assembly of pathway components

3) signal reception often leads to the generation within the cell of a "second messenger"

4) protein kinases and protein phosphatases are activated or inhibited

5) signals are amplified by enzyme cascades

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What is meant by the generation within the cell of a "second messenger"

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-a molecule or ion that can diffuse to other sites in the cell and stimulate metabolic changes (cAMP, cGMP), Ca2+, DAG, IP3

- second messenger can greatly amplify the first signal

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What enzymes are commonly involved in signal transduction pathways?

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-kinases catalyze the phosphorylation of target residues of key signal transduction proteins
-phosphatases catalyze dephosphorylation, reversing the effect of kinases

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How are signals amplified by enzyme cascades?

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An enzyme in a signaling pathway, once activated, catalyzes many additional reactions. The enzyme may generate many molecules of the next component in the pathway or activate many copies of the next enzyme in the sequence. This greatly amplifies the signal at each step and offers opportunities to modulate the intensity of a signal.

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How does the adaptive immune system work complimentary to the innate immune system?

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The adaptive immune system produces signals and components that increase the effectiveness of innate responses.

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What is a major difference between adaptive and innate immunity?

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Innate immunity is rapid and utilizes a preexisting but limited repertoire of responding components. Adaptive immunity compensates for its slower onset by its ability to recognize a much wider repertoire of foreign substances and also by its ability to improve during a response, whereas innate immunity remains constant.

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What are the four characteristics of adaptive immunity?

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1) antigenic specificity - ability to distinguish between two proteins differing in one amino acid
2) diversity- recognize billions of unique structures
3) immunologic memory - a second encounter induces heightened state of immune reactivity
4) self-nonself recognition - only responds to foreign antigens

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antigenic specificity

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of the adaptive immune system permits it to distinguish subtle differences among antigens

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What are the two types of lymphocytes?

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1) B cells
2) T cells

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B cells

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- mature in the bone marrow
- expresses a unique antigen-binding receptor on its membrane

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naive B cell

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- one that has not previously encountered antigen
- binding of the antigen to the antibody causes the cell to divide rapidly; its progeny differentiate into memory B cells and effector B cells called plasma cells

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plasma cells

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-progeny of naive B cells after encountering the antigen divide rapidly into memory B cells and effector B cells
-produce the antibody in a form that can be secreted and have little or nonmembrane bound antibody
- only live for a few days
- secreted antibodies are the major effector molecules of humoral immunity

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memory B cells

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-Antigen committed, persistent B cell. B-cell differentiation results in formation of plasma cells, which secrete antibody, and memory cells, which are involved in the secondary responses.
-Have a longer lifespan than parent and express the same membrane bound antibody as their parent B cell

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T lymphocytes

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a lymphocyte that matures in the thymus and expresses a T-cell receptor, CD3 and CD4 or CD8.
- arise in the bone marrow
- migrate to the thymus gland to mature
-express a unique antigen-binding molecule (T-cell receptor)
- adaptive cellular immunity

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What are the two well-defined subpopulations of T cells?

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1) T helper - display CD4
2) T cytotoxic - display CD8

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T regulatory (Treg) cell

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carries CD4 and CD25 on its surface but may be distinguished from Th and Tc cells by cell surface markers associated with its stage of activation.

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T cell receptors recognize what type of antigen?

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only antigen that is bound to cell membrane proteins called major histocompatibility complex II (MHCII) molecules

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MHC molecules

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major histocompatibility complex molecules are polymorphic glycoproteins found on cell membranes

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What are the two types of MHC molecules?

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1) class I MHC - which are expressed by nearly all nucleated cells of vertebrate species
2) class II MHC - which are expressed only by antigen-presenting cells (APC's)

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cytotoxic T lymphocytes (CTL's)

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response to the induction of T cells to exhibit cell killing or cytotoxic activity. Have a vital function in monitoring the cells of the body and eliminating any that display antigen, such as virus-infected cells, tumor cells and cells of a foreign tissue graft.

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What does activation of both the humoral and cell-mediated branches of the immune system require?

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cytokines produced by Th cells.

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Describe a safeguard for unregulated activation of Th cells.

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Th cells can recognize only antigen that is displayed together with class II MHC molecules on the surface.
- includes macrophages, B lymphocytes and dendritic cells which are distinguished by two properties:

1) they express class II MHC molecules on their membranes

2) they can produce cytokines that cause Th cells to become activated

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How do antibodies work in the humoral immune system?

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Antibody functions as the effector by binding to antigen and facilitating its elimination.
- crosslinking forming clusters that are readily ingested by phagocytic cells
- activation of the complement system resulting in lysis of the foreign organism
- neutralize toxins or viral particles by coating them to prevent binding with the host

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How do antibodies work in the cell mediated immune system?

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Both activated Th cells and cytotoxic T lymphocytes serve as effector cells.
- cytokines secreted by Th cells can activate various phagocytic cells allowing them to phagocytose and kill microorganisms more effectively
- especially important in ridding the host of bacteria and protozoa
- CTL's participate by killing altered self cells, including virus-infected cells and tumor cells.

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antigenically commited

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the state of a mature B cell displaying surface antibody specific for a single immunogen.

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What is the function of MHC molecules?

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(major histocompatibility complex)
- required for antigen presentation to T cells and for rapid graft rejection
-function as antigen-recognition molecules but they do not possess the fine specificity for antigen characteristic of antibodies and T-cell receptors.
- molecule can bind to a spectrum of antigenic peptides mostly derived from the degradation of protein molecules

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clonal selection

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The antigen mediated activation and proliferation of members of a clone of B cells that have receptors for the antigen (or for complexes of MHC and peptides derived from the antigen, in the case of T cells)
- an antigen binds to a particular T or B cell and stimulates it to divide repeatedly into a clone of cells with the same antigenic specificity as the original parent cell.
- provides a framework for understanding the specificity and self-nonself recognition that is characteristic of adaptive immunity.

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How is specificity achieved in clonal selection?

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only lymphocytes whose receptors are specific for a given antigen will be clonally expanded and thus mobilized for an immune response

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How is self-nonself discrimination accomplished in clonal selection?

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by elimination, during development, of lymphocytes bearing self-reactive receptors or by the functional suppression of these cells if they reach maturity

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How is immunologic memory achieved in clonal selection?

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the number of lymphocytes specific for a given antigen is greatly amplified
- these memory cells have a longer life span than the naive lymphocytes from which they arise

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What are some common manifestations of immune dysfunction?

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1) allergies and asthma
2) graft rejection and graft-versus-host disease
3) autoimmune disease
4) immunodeficiency

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autoimmunity

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malfunction of the immune system by losing its sense of self and nonself which permits and immune attack on the host (MS, Crohns disease, Rheumatoid arthritis)

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immunodeficiency

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Any deficiency in the immune response. It may result from a defect in phagocytosis, the humoral response, or the cell-mediated response. Combined immunodeficiencies affect both the humoral and cell-mediated immune response.

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SCID

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severe combined immunodeficiency affects both B and T cells and may result in death from infection at an early age if untreated

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What happens if a virus is inside a cell and what type of immunity is displayed?

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- macrophage kills the cell
- cellular immunity

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What happens if a virus is prevented from entering a cell and what type of immunity is displayed?

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- virus is trapped by antibody - antibody binds to it
- humoral immunity