Term
| What is a type 1 hypersensitivity Rxn? |
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Definition
Immediate hypersensitivity. A humoral immune rxn mediated by mast cells. IgE antibodies. Allergies such as poison ivy.
Allergen is presented by APC --> Th2 t-cell activates a B cell and produces IgE and IgE binds to Mast cells --> histamine and other mediators. |
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Term
| What is a type 2 hypersensitivity rxn? |
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Definition
| Antibody mediated. IgM and IgG. Opsonization, activation of complement, Neutrophils, Abnormal cells. Normally present. A naive B cell recognizes an abnormal self antigen, becomes activated. IgG leads to opsonization or classic complement. IgG attracts complement, can damage membranes. |
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Term
| What is a type 3 hypersensitivity Rxn? |
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Definition
| A type of humoral immunity, immune complexes. Normally not present, sites of inflammation where complexes fall out of solution - SLE.IgM and IgG |
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Term
| What is a type 4 hypersensitivity rxn? |
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Definition
| Cellular immunity. CD4 T cells - cytokine mediated and CD8 T cells - direct cytolysis. No antibodies are involved. CD4 releases IFN--> damage to membrande. CD8 kills cell directly. |
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Term
| What is the difference between CD4 and CD8 cells? |
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Definition
Effector cells remove the antigen, or T cells turn into memory cells.
CD4 cells - activate macrophages, B cells --> inflammation. MHC II
CD8 cells - Kills the infected target cells, macrophage activation. MHC I |
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Term
| What is the purpose of T cell activation? |
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Definition
| Activate transcription of genes that mediate responses and functions of activated T cells. |
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Term
| What are the three signals required for T cell activation? |
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Definition
1) Interaction of antigen and MHC with the T-cell receptor
2) Co-stimulators and adhesion molecules
3) Release of IL-2 and upregulation of IL-2 receptors. |
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Term
| How does the first signal work for T cell activation? |
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Definition
| the TCR is a co-receptor specific for MHC protein, not the antigen. This interaction leads for weak signal. CD4 recognizes antigen. CD3 can block lymphocyte activation. |
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Term
| How does the 2nd signal work for T cell activation? |
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Definition
Activated APCs - increased co-stimulators and cytokines. B7 on APC binds to CD28 on T cell. When activated cells are downregulated, T-cells express CTLA-4 which is competetive for B7, and stops activation.
CD40 is a co-receptors on T-cells and Bcells, enhances the expression of B7 and cytokines. Makes APCs better. |
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Term
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Definition
| LFA is an integrin on the Tcell and ICAM is a ligand for the integrin on the antigen presenting cell. Allows for strong T-cell adhesion --> T cell response. |
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Term
| How does the 3rd signal work for T cell activation? |
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Definition
| Signals 1 and 2 lead to secretion of IL-2 and upregulation of the IL-2 receptor --> T cell proliferation |
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Term
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Definition
| CD20 is found only on B cells. B cells act as APCs, CD20 can be attacked to interfere with production of antibodies. |
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Term
| What disease states are associated with Type I rxns? |
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Definition
- Bronchial asthma
- Allergic rhinitis
- Food Allergies
- Systemic anaphylaxis |
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Term
| What diseases are associated with type 2 immune rxns? |
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Definition
- Autoimmune hemolytic anemia - RBC antigen
- Autoimmune thrombocytopenia - platelet antigen
- Goodpasture's syndrome - kidney/lung antigen
- acute rheumatic fever - myocardium antigen
- Hashimoto's - thyroid tissue antigen |
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Term
| What is a type 2 cytotoxic rxn? |
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Definition
| A reaction where antibodies prevent a physiologic response, not direct cell damage. Ex: inhibition of binding. |
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Term
| What diseases are type 2 cytotoxic rxns? |
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Definition
- Myasthenia gravis - blocks/destroys AcH receptors
- Graves disease - TSH receptor stimulated --> hyperthyroidism
- Pernicious anemia - Decreased B12 in parietal cells --> abnormal RBC/anemia |
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Term
| What types of diseases are type 3 immune rxns? |
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Definition
- Systemic lupus - antigen is DNA/nucleoproteins
- RA - unknown antigen
- Glomerulonephritis - strep cell wall antigen |
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Term
| What diseases are type 4 immune reactions? |
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Definition
- Type I diabetes - Beta cells of the pancreas
- RA - also a type 3 rx
- Inflammatory Bowel Disease - GI bleeding, unknown antigen
- PPD - a delayed-type rxn after T cells have been sensitized |
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Term
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Definition
| In chronic Type 4 rxns, if an antigen cannot be eliminated, cells containing the antigen are walled off to form a granuloma. |
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