Immune mechanism is designed to protect body against invading microorganisms and foreign potentially harmful molecules.There are four types of immune mechanism; the nature of invading antigen determines which type of mechanism bought into action.Certain antigen promotes exaggerated response called hypersensitive reaction or an allergy, which may be harmful to body tissues.
Type 1 reaction is allergic response to foreign substances usually protein entering the body it is a immediate reaction occurs within the minutes or hours of antigen entering the body.In type 1 response the antigen enters the body and stimulate B-lymphocyte to produce antibodies. These antibodies adhere Mast cells in the vessel wall, they neutralizes the antigen and the Mast cell releases the chemical which causes streaming eyes, sneezing symptomatic fever.
In type 2 reactions is initiated by antigens, which are part of tissue cell. Antigen enters the blood stream and invokes the production of antibodies.Antibodies destroy the antigens, but also cause cross reaction with the blood cell which can lead to cell damage, example Mismatch Blood transfusion in which antibodies are formed against donor red cells, which leads to their destruction.
In type 3 reactions is a immediate reaction occurring within few hours of antigenic stimulation. Antigen enters the blood stream, which already filled with antibodies formed during the previous exposure with same antigens.Antibodies form a complex with antigen a blood protein called complement. The complex may damage tissue such as glomeruli in kidney by blocking the capillaries.
Type 4 Reaction is a delayed immune response, which occurs more than 24 hours after the initial contact with the antigen. The antigens enter the blood stream, where it stimulate T lymphocytes to produce antibodies, which remain attached to the cell wall, the anitbodies, and then destroys the antigens.Once T-lymphocytes are been sensitized by antigens the can produce antibodies and confer immunity
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