The immune response is a two-pronged attack against a pathogen, consisting of the cell-mediated immune response and the humoral immune response.

T-cells or T lymphocytes are responsible for a cell-mediated immune response. Hence, it is also known as T-cell immunity. This sort of immune response is designed to protect against infections that can enter host cells.

T-cell surfaces contain receptor molecules that can bind to antigens. Similar to the variable part of the humoral antibody, these receptor molecules are composed of a variable unit. Each T-cell contains approximately 100,000 receptor sites.

When an antigen enters the body, macrophages immediately assault and fragment the antigen. The antigen is then presented to the T-helper cells. T helper cells identify the antigen and initiate a cascade of cell-mediated responses.

T-lymphocytes first form a clone after being stimulated by T-helper cells. There are various types of T-cells that are morphologically identical but functionally distinct.

The actions of the different types of T-cell

Helper cells respond by generating lymphokines, which are tiny peptide compounds. The lymphokines boost the proliferation of additional T-cells, stimulate B cells to generate antibodies, and aid in the accumulation of macrophages and phagocytosis in inflamed tissues.

Cytotoxic cells or Killer cells kill cells infected by viruses, cancerous cells and transplants.

The third type of T-cells, suppressor cells, create lymphokines that inhibit the activity of phagocytes and several types of WBC cells. They contribute significantly to immunotolerance.

Some of the cells persist as memory cells that become stuck throughout the body's lymphoid tissue. A repeat exposure to the same antigen can elicit a faster immunological response than the initial exposure.