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2 Forms of Immunity
- Cellular Response (lymphocytes - direct response, detect foreign cell/material)
- Humoral Response (antibodies circulate in the blood)
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What are the 2 types of lymphocytes
- B - Cells - (derived from bone marrow, matures in Butt?)
- T- Cells - (originate from the bone marrow, matures in the Thymus)
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What do B-cells do?
B-cells react when antibodies come into contact w/ antigen. B-cells differentiate into plasma cells. Plasma cells then produce antibodies specific for the antigen stimuli of original B-cell.
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What are the 5 processes of B-cell differentiation, maturation, and activation?
- 1. pre-B cell: contain receptors on plasma membrane but no surface immunoglobulin (NO IDENTITY)
- 2. early-B cell: immature... recognized by surface IgM and later IgD
- 3. isotype switching: expression on the surface of other immunoflobulins - IgG, IgA, IgE
- 4. mature B-cells: constitute 10-20% of pperipheral lymphocytes awaiting activation by foreign Antigen (sensitization) immunogl. isotypes IgG, IgM, IgA
- 5. Plasma Cells: make antibodies, requires exposure to additional T-cell products but sometimes cytomegalovirus activation can be direct
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Specificity of B-cells and memory
During activation B-cells dividing under modulation of T-cells, most of the new B-cells become a "selected clone" of the plasma cells and pump out specific antibodies.
When the immune system "wins" the plasma cell dies, but plenty of the B-cell clones survive and have memory --> future presence of that same antigen will trigger greater antibody response
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What do T-cells do?
- T cells DO NOT USE ANTIBODIES nor have them on their surfaces.
- But specificity of the antigen recognition is guaranteed by the receptor presented on the plasma membrane.
- Important for protection against Tumors, intracellular bacteria, viruses, parasites, and reactions to transplant
- Centerpiece of immune system
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What are the 3 basic mechanisms for which most of T-cell functions?
- 1. some are DIRECTLY CYTOTOXIC
- 2. some participate in RELEASE of vaious CYTOTOXIC MEDIATORS
- 3. some are involved in STIMULATION of B-Lymphocytes
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What are the different T-Lymphocyte subtypes?
- CD4 - helper "commander"
- CD8 - Cytotoxic "soldier"
- CD3 - ???
they're categorized by expression of specific surface marker proteins --> CD - cluster designations
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What are the 4 differentiations of T-lymphocytes?
- Early cortical T-cells (least mature thymocytes, make up 10% of all T-lymphocytes)
- Late cortical T-cells (thymocytes that account for 80% of thymic populsion
- Medullary T-cells (CD-4 helper 50% and CD-8 Cytotoxic 50%, located in medulla of thymus)
- Peripheral T-cells (T-lymphocytes released to the blood with 65% (Cd-4 helpers) and 35% (Cd-8 cytotoxic)
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What are natural killer cells (NK)?
- 10-15% of Blood lymphocytes
- NK's are the First line of defense vs neoplastic tumors and virus infected cells since they can lyse them without prior sensitization
- special type of Large lymphocytes (formerly known as non-t/-non-B or NULL cells)
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What are hypersensitivity reactions and how are they classified?
- They are immune responses to antigiens that can cause tissue damaging reactions
- Resultant tissue lesions --> Hypersensitivity disease
- They're classified on the basis of the mechanism mediating the disease
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Type I hypersensitivity
- Mediated by IgE antibody sensitization
- immune response release vasoactive mediators from MAST cells or Basophils that affect vascular permeability and smooth muscle
- "ALLERGY reaction" --> activation of MAST cells, Basophils, releasing:
- 1. Histamine as primary mediator
- 2. Prostoglandins, lukotrienes as secondary mediators
- Can be 1. LOCAL - (itching swelling sneezing, eyes and nasal)
- 2. GENERALIZED - (bronchoconstriction, cirulatory collapse, Anaphylactic shock/syndrome)
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Type II hypersensitivity
- IgG and IgM Mediated
- Classes of antibody participate in indirect cytotoxicity
- Antibodies binding to an antigen on surface of cells --> induce activation of COMPLEMENT which leads to target cell destruction by:
- 1. DIRECT LYSIS (membrane attack complex C5-9)
- 2. OPSONIZATION (enhancing phagocytosis (C3b)
- Examples: (many autoimmune disease eg Hemolytic anemia, Graves disease, Myasthenia Gravis)
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Type III hypersensitivity
- Antigen - Antibody Complex disease
- Mediated IgM, IgG, IgA complexes formed in circulation and deposted in different tissues -->
- presence acitivates complements, Chemotaxis (of neutrophils --> trigger acute inflam rxn impairing tissue fx
- examples: SLE or Lupus
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TYPE IV hypersensitivity
- cell-mediated immmune response (NO ANTIBODIES)
- antigens are processed bt macrophages and presented to cytotoxic T-cells --> their activation relaease of mediators
- --> destroying plasma membrane and target cells
- examples: Sjorgen syndrome
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