Cellular mediated Immunity

Cell mediated immunity consists of immune activities that differ from antibody- mediated immunity. It is moderated by the link between T-lymphocytes and phagocytic cells. T-lymphocytes do not directly recognize the antigens of microorganisms or other living cells, but rather when the antigen is present on the surface of an antigen- presenting cell, the macrophages. Lymphocytes are immunologically active through various types of direct cell-to-cell contact and by the production of soluble factors.
It is moderated by the link between T-lymphocytes and phagocytic cells

Cell mediated immunity is responsible for the following immunologic events:

• Immunity to intracellular organisms
• Rejection of foreign tissue grafts
• Immunity to viral and fungal antigens
• Delayed hypersensitivity

Cell- Mediated Response

Sixty to eighty percent of the total circulating lymphocytes are T cells derived from progenitor cells that mature in the thymus gland under the influence of thymic hormones. These cells are responsible for cellular immune responses and are involved in the regulation of antibody reactions either by helping or suppressing the activation of B-lymphocytes.

There are at least three functionally distinct types of T cells: cytotoxic or effector T cells, helper or regulatory T cells, suppressor T cells

Cytotoxic T cells: are effectors cells, found in the peripheral blood that have the capacity to kill other cells. These cells can destroy virally infected cells.

Helper T cells: secret a variety of substances that help B cells make antibody response, stimulate activated T cells to proliferate, and activate macrophages. T helper cells control many B cell functions, including proliferation and differentiation.

Suppressor T cells: are thought mainly to inhibit the response of helper T cells. T suppressor cells are capable of suppressing a variety of T cell functions such as cytotoxic response, and B cell responses such as suppression or T helper cells or antibody synthesis by plasma cells.
All T-cells have antigen receptor protein (T cell receptor) with which they bind foreign antigens. In order to recognize a foreign antigen, T- cells must simultaneously recognize particular types of self-antigens, which are structural components of the surface of human cells. These antigens don’t normally stimulate a destructive immune response.

The antigen-binding site of a T-cell must simultaneously recognize and bind both a foreign and a self-antigen. The self-antigen is known as major histocompatibility complex (MHC), it has two major classes:
Class I major histocompatibility complex antigen present on all nucleated cells of the body, it is recognized by only T cytotoxic cells. Class II major histocompatibility complex antigen, present only on macrophages, it recognized by only T-helper cells.

The first cell to be activated in any immune response is the T helper cell. Activation of T helper cell is enhanced by some factors produced by macrophages. The stimulated T helper cell stimulates itself and proliferate in increased amount. This activated T helper cell also helps to stimulate T cytotoxic cells.

When these cells recognize antigen presented in combination with the class I major histocompatibility antigen. Activated T cells respond with direct cytotoxic killing (T cytotoxic cells) or with immune regulation either by intensifying the immune response (T helper cells) or by lowering the immune response (T suppresser cells).

Helper and suppressor T cells are the principal regulators of immune responses. Sensitized T cells protect the human body against infection by mediating intracellular pathogens that are viral, bacterial, fungal, or protozoal. In addition, T cells are responsible for chronic rejection in organ transplantation.

Delayed Type of Hypersensitivity

Cell- mediated immunity consists of immune activates that differ from antibody mediated immunity. Cell-mediated immunity is moderated by the link between T lymphocytes and macrophages. T cells do not recognize the antigen of microorganisms or other living cells but are immunologically active through various types of direct cell-to-cell contact and by the production of soluble factors.

The delayed type reaction is cells mediated and involves antigen sensitized T cells, which respond directly or by the release of lymphokines to exhibit contact dermatitis and allergies of infection. Delayed hypersensitivity reaction is one of cell mediated immunity immunologic events e.g. Tuberculin test.

Cellular mediated Immunity Cellular mediated Immunity Reviewed by gafacom on July 11, 2020 Rating: 5

No comments:

Powered by Blogger.