Immunology Intro

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4 roles of the immune system: 1. Defense against infections.
2. Response to tissue grafts, newly introduced proteins.
3. Defense against tumors
4. Antibodies recognize any class of molecules.
Components of innate immunity: Mast cell
Dendritic cell
Macrophage
Natural Killer Cell
Granulocytes: Basophils, Eosinophils, Neutrophils
Complement Proteins

BOTH Innate and Adaptive:
Natural killer T cells, γδ T cells.
Components of adaptive immunity: B cells and antibodies they produce.

T cells: CD4+ and CD8+

BOTH Innate and Adaptive:
Natural killer T cells, γδ T cells.
Characteristics of Innate Immunity: Responds in minutes-hours.
Specific for molecules and molecular patterns seen in pathogens.
Perfect self/nonself discrimination.
No memory response.
Diversity limited
Characteristics of Adaptive Immunity: Responds in days.
Highly specific: detects tiny differences in molecules.
Highly diverse: many receptors.
Very good self/non-self discrimination but with some failures.
Persistant memory.
PAMP: pathogen associated molecular pattern
PRR: pattern recognition receptor
Lymphocytes: types and functions: Function: specific recognition of antigens.

B-lymphs: mediators of humoral immunity
T-lymphs: mediators of cell-mediated immunity
NK cells: cells of innate immunity
Antigen-presenting cells: types and functions: Function: capture antigens for display to lymphocytes.

Dendritic cells: initiation of T cell responses
Macrophages: initiation and effector phase of cell-mediated immunity.
Follicular dendritic cells: display of antigens to B lymphocytes in humoral immune responses.
Effector cells: types and functions: Function: elimination of antigens.

T-lymphs: helper T cells and cytolytic T lymphocytes
Macrophages/Monocytes: cells of mononuclear phagocyte system
Granulocytes: neutrophils, eosinophils.
T-lymph vs B-lymph maturation: B: bone marrow stem cell -> bone marrow until mature -> blood -> lymph nodes/spleen/lymphoid tissues.

T: bone marrow stem cell -> thymus until mature -> Blood, lymph -> lymph nodes/spleen/lymphoid tissues.
Actions of B lymphocytes: Detects microbe -> produces antibodies (humoral immunity) -> Neutralization of microbe, phagocytosis, complement activation
Actions of helper T lymphocytes: Antigen presented to helper T by APC -> Cytokine production ->
Activation of macrophages
Inflammation

Activation (proliferation and differentiation) of T and B lymphocytes
Actions of cytolytic T lymphocytes: Killing infected cells
Actions of natural killer cells: Killing infected cells
Humoral vs. Cellular immunity: Humoral: EXTRAcellular microbe (eg. bacteria)

Cellular: INTRAcellular microbe (eg. virus)
Clonal selection/expansion: An antigen "selects" a previously existing lymphocyte.
Lymphocyte binds to antigen, and if it gets a co-stimulator signal, divides via mitosis, "expansion".

Eventually results in pool of antibody making plasma cells, and a pool of "memory" B cells.

This allows the adaptive immune system to keep pace with rapidly proliferating microbes.
Primary vs Secondary response: Primary is initially weaker, secondary stronger after "memory" B cells produced.
5 Phases of Adaptive Immune Response: Antigen recognition
Lymphocyte activation
Effector phase (cell-mediated or humoral)
Decline (homeostasis)
Memory
MHC: Major histocompatibility complex:
Locus on human genone encoding genes for immune related proteins (HLAs).
HLA: human leukocyte antigen: HLA molecules are the antigen presenting molecules!
Class I HLA molecules: HLA-A, HLA-B, HLA-C

Found in almost ALL nucleated cells in body.
Class II HLA molecules: HLA-DR, HLA-DQ, HLA-DP

Found in "professional" antigen presenting cells (macrophages, dendritic cells, activated T cells, B cells).
Significance of MHC codominant expression:: both parental alleles are expressed, leads to greater variety in MHC molecules for better peptide presentation
Significance of MHC polymorphism:: Many different alleles are present in the popuation, results in different individuals presenting and responding to different microbial peptides.
Significance of class I, class II.: Class I: CD8+ CTLs can kill ANY virus infected cell

Class II: CD4+ helper Ts interact with dendritic cells, macrophages, B lymphs.
CTL: cytotoxic T cell
CDs: full name and function: Cluster of Differentiation Antigens:

Cell surface molecules recognized by diagnostic antibodies... used as markers for cell identification. CDs function in cell-cell interaction, adhesion, signal transduction etc.
APC: antigen presenting cell
Cytokines: protein hormones produced by cells that effect other cells
Chemokines: small cytokines involved in activation and MIGRATION of cells
Interferons (IFN): cytokines produced by cells which can protect against viruses
4 properties of cytokines: 1. Produced in response to antigen.
2. Usually acts on same cell that produces cytokine, or nearby cells (autocrine/paracrine)
3. Pleiotrophism: each cytokine has multiple biologic actions
4. Redundancy: multiple cytokines have or similar biologic properties.
IL-2: principle action, cellular sources: T cell growth stimulation

CD4+, CD8+ T cells
IL-4: principle action, cellular sources: B cell switching to IgE

CD4+ T cells, mast cells
IL-5: principle action, cellular sources: Activation of eosinophils

CD4+ T cells, mast cells
IFN-γ: principle action, cellular sources: Activation of macrophages

CD4+, CD8+ T cells, NK cells
TGF-β: principle action, cellular sources: (Transforming growth factor)

Inhibition of T cell activation

CD4+ T cells; many other cell types.

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