Name 4 main hypersensitivity types and explain how they make make reactions in human body

Sure, here are the four main types of hypersensitivity reactions:

1. Type I Hypersensitivity: This is also known as immediate or anaphylactic hypersensitivity. The reaction may involve skin (hives), eyes (conjunctivitis), nasopharynx (rhinitis), bronchopulmonary tissues (asthma) and gastrointestinal tract (gastroenteritis). The reaction occurs rapidly, usually within minutes after exposure to an antigen. The antigen binds to IgE antibodies which are bound to mast cells and basophils. This triggers these cells to release substances like histamine, causing an inflammatory response.

2. Type II Hypersensitivity: This is also known as cytotoxic hypersensitivity. The antigens are normally endogenous, although they may also be exogenous chemicals, drugs or infections. The reaction involves IgG and IgM antibodies directed against these antigens, leading to destruction of cells by complement activation or antibody-dependent cell-mediated cytotoxicity.

3. Type III Hypersensitivity: This is also known as immune complex hypersensitivity. The reaction involves the formation of antigen-antibody complexes, mainly IgG antibodies, which deposit in tissues like blood vessels, kidneys and joints. This leads to complement activation, recruitment of inflammatory cells, release of enzymes and cytokines, and tissue damage.

4. Type IV Hypersensitivity: This is also known as delayed type hypersensitivity. This reaction is mediated by T cells rather than antibodies. It usually takes 48-72 hours to develop. Antigens are taken up by antigen presenting cells (APCs), processed and presented to T cells, leading to their activation and release of cytokines. This results in inflammation and macrophage activation. Examples include contact dermatitis, tuberculin reaction, and graft-versus-host disease.