Hypersensitivity

There four types of hypersensitivity

Type I: Immediate Mast cell and IgE mediated (histamine, prostaglandins), Asthma, Rhinitis

- Delayed phase eosinophilia due to CD4+ producing Th2 releasing IL-4, IL-5

Type II: Anibody mediated (i.e. autoimmunity- pemphigus, red cell transfusion)

- In the skin these are IgG and IgM antibodies to keratinocytes to induce complement, also CD8+ which causes lysis and extraepidermal blisters.

Type III: Immune complex mediated (causes vasulitis, lupus erythematosous)

- Deposited on vessel walls, induces complement, damages endothelium, causes platelet aggregation

Type IV: Delayed Cell mediated response ( poison ivy, nickle)

- Granuloma, formed when the infection cannot be resolved (i.e. TB)

Cells:  Langerhans Cell, Keratinocytes, Melanocytes, y-delta T-cells all in epidermis; Mast Cells, Fibroblasts, Endothelial, Dermal Dendritic Cells, Dermal Macrophages, T-cells in Dermis; Skin appendages.  

1. Neutrophils (Granules contain myeloperoxidase, cytochrombe b , phosphatase)

2. Eosinophils (Granules stain red with eosin)

• Involved in phagocytosis in allergies and parasitic infection, IL-4 and IL-5 from Th2 induce

3. Basophils (granules stain blue with methylene blue and contain heparin and histamine)

• These are involved in parasitic infections also and are the tissue equivalent of mast cells

4. Monocytes (Antigen Presenting Cells)

5. T-cells

• Th1 responds to APC IL-12 release and induces IFN-y and IFN-a to recruit granulocytes and ^MHC
• Th2 responds to APC IL-10 release and induces IL-3, IL-4, IL-5 to activate B-cells and granulocytes
• CD8+ responds to IL-4, IL-6 from CD4 and MHCI presentation to kill via TNF-a and ^MHC via IFN

6. B-cells

• Secrete antibodies (IgM then IgG, IgE and IgD in allergy)