Evaluation of cell-mediated immunity

Evaluation of cell-mediated immunity:

Although humoral immunity is an important host defense against many bacterial and viral diseases, in many other bacterial infections (especially intracellular infections such as tuberculosis) and viral infections, it is primarily the cell-mediated arm that imports resistance and aids in recovery. Furthermore, cell-mediated immunity is important in defense against fungi, parasites and tumors and in the rejection of organ transplants.
The constituents of the cell-mediated system include several cell types:
1. Macrophages: Which present the antigen to T cells.
2. Helper T cells: Which participate in antigen recognition and in regulation (helper and suppressor) functions.
3. Natural killer (NK) cells: Which can inactivate pathogens.
4. Cytotoxic T cells: Which can kill virus-infected and tumor cells with or without antibody.
Macrophages and helper T cells produce cytokines that activate helper and cytotoxic T cells, leading to the killing of the pathogens or tumor cells.

1- Delayed (cell-mediated) Hypersensitivity (type IV):
Is a function of T lymphocytes, not antibody. The macrophage ingests the antigen, processes it, and presents an epitope on its surface in association with class II MHC protein. The helper T (Th-1) cell is activated and produces gamma interferon, which activates macrophages. These two types of cells mediated delayed hypersensitivity. It can be transferred by immunologically sensitized T cells, not by serum.
The response is delayed ex. It starts hours (or days) after contact with the antigen and often lasts for days. In certain contact hypersensitivity, such as poison oak, the pruritic, vesicular skin rash is caused by CD8-positive cytotoxic T cells that attack skin cells that display the plant oil as a foreign antigen. In the tuberculin skin test, the indurations of skin rash is caused by CD4-positive helper T cells and macrophages that are attracted to the injection site.