Immune system

The function of immune system is protection against foreign bodies. Each cell contain specific macromolecules on it’s surface, that differ between species and even between individuals of the same species. Immunity consist in ability to recognize self cells and distinguish from foreign cells, for example viruses and microbes. Macromolecules that cause immune response are called antibodies, most often they are proteins.

Specialized and very efficient weapon against antigens are antibodies – immunoglobulins. Immune response that engage antibodies is called humoral immunity. Antibodies are produced by B lymphocytes (B cells). Human body generates variety of antibodies. Genes that codes for these proteins origin as a result of DNA rearrangement. This mechanism enable producing a huge number of combinations from certain number of DNA fragments coding for special parts of the immunoglobulin. Additionally also new mutations can appear. Antibodies do not directly destroy antigens. They combine with them and cause their destruction by specialized cells.

Immune reaction that destroys foreign cells is called cellular immunity. It protects against viruses, cancers and causes rejection of organ transplants. T lymphocytes (T cells) participate in the process. Cellular immunity is controlled by a group of genes called major histocompatibility complex, MHC. Proteins coded by these genes, major histocompatibility antigens, can be found on the surface of nucleated cells. They enable distinguishing between self and foreign cells and take part in regulating immune system cells’ behavior during immune response.