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Humoral and Cell Mediated Immune Response

The immune response is of the following two types:

(1) humoral response and

(2) cell mediated response.

The humoral, immune response is based on antibodies; it can be conferred on nonimmune individuals by administration of serum antibodies from an immune individual. Antibodies act as the effector of humoral response.

They bind to the antigens and, thereby, facilitate their elimination, e.g by forming clusters (1) rough cross linking of antigen molecules, which are readily ingested by phagocytic cells. Binding of antibodies to a microorganism can activate the complement system, which lyses the microorganism. Antibodies bind to toxins and viral particles, and prevent their subsequent, binding to host cells.

In contrast, cell-mediated immunity is based on T cells, which are a type of lymphocyte. T cells are of the following two types: T helper (TH) and T cytotoxic (Tc) cells. When a TH cell interacts with an antigen-MHC II molecule complex present on an APC, it becomes activated and begins to secrete cytokines.

These cytokines activate B cells, Tc cells, and various phagocytic cells. Activated phagocytic cells are able to kill microorganisms like bacteria and protozoa more effectively. When a Tc cell interacts with an antigen-MHC I complex, the Tc cell proliferates under the influence of cytokines produced by activated TH cells.

These Tc cells differentiate into cytotoxic T lymphocytes (CTLs). The CTLs kill all such cells that display foreign antigens complexed with MHC I molecules. Such cells are called altered self-cells; they are usually virus-infected cells, tumour cells and foreign tissue cells. Thus TH cells and CTLs are effectors of the cell-mediated immune response.

 
 

 
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