Humoral Immunity and Cell Mediated Immunity Complete

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Humoral immunity and cell-mediated immunity are two branches of adaptive immunity. What mediates humoral immunity? What are the targets of humoral immunity?	Humoral immunity is a B-cell antibody mediated response directed against extracellular microbial pathogens (Especially encapsulated bacteria), certain intracellular microbial pathogens (viruses), and microbial toxins.
What is the difference between the recognition phase and effector phase of humoral immunity?	Th recognition phase involves the identification of antigens via membrane-bound immunoglobulins (IgM and IgD) on the surface of the naive B cell. The effector phase is characterized by secretion of immunoglobulins from plasma cells. (ie mature B cells)
A primary response is generated when an antigen is first encountered. Second, exposure to that same antigen is known as the secondary exposure. What are the key differences between primary and secondary responses? What accounts for these differences?	The primary response has a longer lag period (time until antibody is produced) and is typically characterized by IgM followed by low amounts of IgG. The secondary response is characterized by a faster and larger production of IgG that persists longer. These differences are due to antigen specific memory B cells in the secondary response.
What is affinity maturation?	Process that selects for B cells producing antibodies of highest affinity to an antigen of interest through successive exposure to that antigen in the periphery
What genetic process drives affinity maturation?	Somatic hypermutation results in random and rapid point mutation in variable gene segments of V(D)J genes, modifying the affinity of a B cell's immunoglobulin. The B cells expressing immunoglobulins with highest affinities are then selected through interaction with antigen.
What is the name of the process by which immature B cells expressing immunoglobulins with a high affinity for self-antigens are restricted from becoming mature?	Negative selection. An analogous process occurs with T cells
What type of cell stimulates B cell clonal expansion, isotype switching, affinity maturation, and differentiation into memory B cells?	Helper T cells (CD4+/CD8-)
What are the two types of cells that may become activated B cells?	Plasma cells, which are responsible for secretion of antibodies. memory B cells, which undergo affinity maturation and may differentiate into plasma cells upon reexposure to the antigen.
Will a single antigen with a single epitope activate a B cell?	No. B cell activation is dependent on the cross-linking of membrane-bound IgM and IgD, which requires more than one epitope. (This is true for most antigens, but there are plenty of examples of monomeric soluble protein antigens where cross-linking is not required and T-cell helps overcome this requirement)
How do B-cell and T-cell receptors differ with respect to the native form (ie, three dimensional shape) of the antigen?	T-cell receptors recognize only a linear peptide sequence that results from processing within an antigen-presenting cell (APC). The B cell receptors can recognize the native form of the antigen.
B-cell proliferation, early antibody secretion, and isotype switching occur in which area of the lymphoid follicle?	These early-phase, T-cell dependent responses occur in the marginal zone.
B-cell affinity maturation and isotype switching occur in which area of the lymphoid follicle?	These late-phase events occur in the germinal centers. Isotype switching can occur in the early or late phases and in two seperate locations.
What processes can result from interaction of CD40 on B cells with CD40L on T cells?	Isotype switching, B cell activation and affinity maturation. The T cell cytokines also play a role in these processes.
Steps in B cell maturation	1. B cell receptor (BCR) binds antigen on pathogen, endocytoses, and proteolyses pathogen and presents antigen on MHC-2. Antigen is then bound by TCR. B7 of B cell binds to CD28 of T cell. B7-CD28 complex causes expression of CD40L on T cell, which binds to CD40 on B cell, thus activating B-cell isotype switching. CD40-CD40L is also necessary but not sufficient for B-cell affinity maturation. Activation of t cell via B7-CD28 complex also causes the release of cytokines, which enter the B cell and signal proliferation (IL-2), isotype switching (IL-4 for IgE, IL-5 for IgA) and affinity maturation. A combination of cytokines and CD40-CD40L interaction results in B-cell proliferation, isotype switching and affinity maturation, all of which result in a more effective immune response against the pathogen on the current and subsequent infections.
The Th-2 subset of T cells, which produce IL-4, cause B cell expression of what isotype?	IgE
TGF-B causes B cell expression of what isotype?	IgA
What cytokine expressed by t cells also cause isotype switching to IgA?	IL-5
What is a hapten? How are antibodies generated against haptens?	Haptens are smalll chemicals that are nonimmunogenic. Haptens complex with a carrier protein such that T cells can recognize the hapten-carrier protein complex and activate B cells to generate antihapten antibodies.
When in conjunction with TCR-MHC2 binding, interaction of the CD28 on the T cell with B7 on a B cell or other APC results in what process in T-cell mediated immunity?	Activation of the T cell, causing the secretion of cytokines from the T cell that assist in maturation of the B cell.
Cell-mediated immunity (CMI) and humoral immunity are two aspects of adaptive immunity. What mediates CMI?	T-helper cells (CD4+/CD8-, Th cells), cytotoxic T cells (CD4-, CD8+, Tc cells) macrophages, and natural killer cells.
What is the major difference between how CMI and humoral immunity are elicited by antigen?	Unlike the IgM B-cell antigen receptor, the T-cell receptor (TCR) is not secreted. Immunity must be conferred via direct contact between cells.
Cell-mediated immunity is mainly directed against what two major types of cells?	1. Cells with intracellular microorganisms. 2. Aberrant, endogenous cells such as cancer cells.
Persons with a deficiency in cell-mediated immunity are prone to which types of infections?	Infections with viruses, fungi, Mycobacterium, and other intracellular microorganisms.
What are the two types of naive Th cells? What are their functions?	Th1 cells mediate the inflammatory process and activate macrophages. Th2 cells inhibit both the inflammatory process and macrophage activation and aid in helminth immunity and antibody production.
List the major steps in Th1 cell-mediated macrophage activation	Antigen-presenting cells (APCs) present antigen to naive Th cells, leading to Th1 cell differentiation and sensitization in lymph nodes. Transit of Th1 cells to site of antigen release (ie site of infection) Th1 cell activation of macrophages.
Name the different types of APCs. What two signals are needed to activate a Th cell? What cytokine do APCs secrete to induce Th-1 cell differentiation?	B cells, macrophages and dendritic cells. APC's major histocompatibility complex 2 (MHC-2) molecule with antigen binds to TCR/CD4 and APC's B7 protein binds to Th's cell CD28, providing the necessary costimulation for activation. IL-12 and y-IFN differentiates naive TH cells into Th1 cells.
Th1 cells migrate to source of antigen (infection) and activate macrophages that present the antigen of interest through what three signals?	Interaction of MHC-2 with bound antigen and TCR/CD4 CD40 on macrophage with CD40L on Th1 cell. y-IFN released from Th1 cell with y-IFN receptor on macrophage.
What are the functions of macrophages?	Macrophages present antigens, produce cytokines and perform phagocytosis.
What functions of macrophages are enchanced in T-cell activation of macrophages?	Activated macrophages kill phagocytosed microbes via H2O2, O2-, and NO; trigger acute inflammatin, and facilitate tissue repair by phagocytosis of necrotic tissue.
Delayed-type hypersensitivity (DTH, type IV) is the only cell-mediated hypersensitivity reaction. Describe it and name some examples.	Previously sensitized T cells reencounter the initial antigen and trigger macrophage activation, a process that develops over 24 to 48 hours. Examples include acute transplant rejections, tuberculosis (TB) skin tests and contact dermatitis.
Describe the histopathology of a granuloma. In what instances are granuloma produced?	Granulomas are composed of a central core of activated macrophages surrounded by lymphocytes and are formed in response to persistent antigen stimulation of CMI.
Activated macrophages in a granuloma are also called epitheloid cells due to morphological changes. What cytokine triggers this change?	Y-IFN
How are Tc cells activated?	Tc cells require APC with MHC-1 with antigen of interest binding to TCR/CD8 on Tc cell and costimulation by either B7/CD28 or cytokines (IL-2) from Th cells.
How do activated Tc cells recognize infected cells?	Through presentation of the antigen of interest on the infected cell by the MHC-1 molecule.
How do activated Tc cells kill infected cells?	Perforins (create holes in the cell membranes, disrupts osmotic balance), granzymes (activate apoptosis through caspases) and FasL on Tc cells binds Fas on target cells also resulting in apoptosis.

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Humoral Immunity and Cell Mediated Immunity Complete

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