Explain the role of B-lymphocytes and T-lymphocytes in the defence of the body against a virus infection (6 Marks)

A virus is a pathogen which contains antigens on its cell surface. These antigens are detected and digested by macrophages. The two pathways involved in the detected and elimination of the virus is the cell-mediated response (T- cells), and the humoral response (B-cells). The macrophage presents the antigen to specific B- cells. B- cells will then recognise and bind to the antigen. This will cause the B- cell to become activated and proliferate via mitosis. These B-cells differentiate into plasma cells which secrete antibodies that can bind to the antigen and cause clumping/ agglutination of the virus. Some of the B cells will also differentiate into memory cells, which when exposed to the virus a second time, will stimulate quick proliferation of these specific B- cells (and plasma cells)

Helper T- cells secrete lymphokines and other chemicals which further activate B- cell proliferation. T- cells can also attract phagocytes to engulf the clumped virus via phagocytosis. Lastly, cytotoxic/ killer T- cells kill virus-infected cells by the use of perforin which creates pores in the infected cells. The infected cells then die due to osmotic lysis.