In this article we will discuss about the steps involved in cellular immune response.
Host defenses that are mediated by antigen specific T-cells and various non-specific cells of the immune system is called cell mediated immune responses.
Cellular immune responses have an activation phase and an effector phase.
These phases occur as follows (Fig. 10.2):
1. A viral protein made in an infected cell or an abnormal cellular protein is degraded to fragments and picked up by class I-MHC.
2. A Tc cell receptor recognises processed antigen bound to class I-MHC protein on an infected cell.
3. Co-stimulatory signal from the infected cell causes Tc cell to proliferate and to form a clone of cells.
4. In the effector phase, a Tc cell receptor again recognizes processed antigen bound to a class I MHC protein and releases molecules, such as perform or the Tc cell can bind to Fas receptor on the target cell.
5. Released perform causes lysis of the infected cell. Binding of Tc cell with the Fas receptor on the target cell can cause apoptosis of the infected cell. Cell lysis and apoptosis work in synchronized fashion to eliminate altered host cell.
Cellular immune responses protect against intra-cellular bacteria, viruses and cancer and are responsible for graft rejection, since T-cell receptors recognise self MHC molecules complexed with non-self (in the case of virus-infected cells and in graft rejection) or altered self antigens (in the case of mutated or tumor cells). Transfer of primed T cells confers this type of immunity on the recipient.