Question

In Toxicity and Hypersensitivity, What are the differences between Types I, II,III, and IV hypersensitivities including why they occur and cells (mechanisms) they utilize

Answer 1

There are 4 types of hypersensitivities:-

1. Type 1 hypersensitivity: It is an immune reaction to allergens. Allergens can be defined as any molecules that triggers the allergic reaction from the body. The hypersensitive body treats allergens as if they are pathogen and hence, they trigger the immune response. The cells which involved in this type of reactions are IgE antibodies, mast cells and basophils. When the hypersensitive individuals are exposed to an allergen for the first time, the immune system produces IgE antibodies which bind to the cell membrane of basophils and mast cells. When there is subsequent exposure with the allergen, there is a rapid immune response as IgE antibodies attached to mast cells and basophils bind allergens and initiate degranulation in the white blood cells. In the process of degranulation, mast cells or basophils release granules that contain inflammatory molecules.

2. Type 2 hypersensitivity: It is also called the cytotoxic hypersensitivity. It is the result of antibodies interaction with the body's tissue and thats leads to destruction of the tissue and cells. The antibodies once bound to the membrane of the cell it initiates a chain of reactions and that cause the cell inflammation and eventually cell lysis take place. The cells involved in this type of hypersensitivity are IgG and IgM antibodies. The common examples of this are hemolytic reaction which occur either in case of wrong transfusion of blood or in Rh incompatibility of newborns in subsequent pregnancies.

3. Type 3 hypersensitivity: It is caused by formation of immune complexes in the tissues of the hypersensitive individuals. These complexes are the accumulation of antibodies bound to antigens.These complexes contain more percentage of the antibody concentration than the antigen concentration. These complexes can settle on the tissues where they are triggering the immune response and their location and size make it difficult for the phagocytosis to occur and eliminate but now these masses are exposed to enzymes which break down these masses and consequently damage the tissue where these masses have settled. IgG antibodies are involved in this type of hypersensitivity.

4. Type 4 hypersensitivity: It involves T lymphocyte activity and there is no involvement of antibodies in this. These cells are involved in cell mediated immune response. These are delayed reaction to the antigen. On first contact with allergen, memory T cells are produced and upon subsequent exposure with the similar antigen, the memory T cells generates a quicker and an intense response which also activates macrophages, which eventually damages the body tissues. Chronic asthama is a type 4 hypersensitivity reaction.