Self recognition & self tolerance

What is self recognition?

The ability of your bodies T cells to recognise your own MCH proteins

What is self tolerance?

when your own T cells lack reactivity to peptide fragments of your own proteins

If a person is overly reactive to a substance that is tolerated by most they are said to be allergic or ….

Hypersensitive

How many hypersensitivity reactions are there?

4 - Type I, II, III, IV

which type of hypersensitivity reaction is associated with anaphylaxis?

type I

What must have occurred prior to allergic reaction?

• sensitisation of person to allergen

• re-exposure to allergen

how fast does a type I hypersensitivity reaction take to occur?

only a few minutes

How does a person become sensitised to an allergen?

First exposure = production of IgE antibodies that bind to the surface of mast cells and basophils = increases ½ life of IgE antibodies

Which antibodies are associated with a type I reation?

IgE

what cells to IgE antibodies bind to during sensitisation to an allergen?

basophils and mast cells

Upon next exposure to allergen - what is the immediate response?

• Mast cells and basophils release histamines, prostaglandins, leukotrienes & kinins

• Collectively they mediate vasodilation, increased permeability of blood vessels, increased smooth muscle contractions of airways and increased mucous secretion.

• Ultimately = difficulty breathing, inflammatory response (oedema) and hypotension

Upon next exposure to allergen - what is the late response?

• Migration of leukocytes (especially eosinophils)

• eosinophils release peroxidase = further tissue damage

Which antibodies mediated type II hypersensitivity reactions?

IgM and IgG

Describe TII reaction - example?

Incompatible Blood transfusions

• IgG/IgM direceted against self antigens on persons blood cells/ tissue

• leading to activation of complement = cytolysis

which antibodies are associated with TIII reaction?

IgA and IgM

Describe a TIII reaction

IgA and IgM antibodies form immune complexes, escaping phagocytosis BUT become trapped in basement membrane under endothelium of blood vessels.

• activates complement and causes inflammation

What is the timeframe for TIV reactions?

12-72hrs

Describe T IV reactions - example?

Intracellular bacteria or haptens (poison ivy toxin)

• allergens taken up by APCs migrate to LNs and present antigens to T cells = proliferation

• T cells return to site of entry and produce interferon gamma = activates macrophages and TNF = stimulates inflammatory response