Describe how vaccination can lead to protection against bacterial meningitis (6 marks)

Vaccines provide a dead/inactive form of bacterial meningitis. Phagocytes such as macrophages recognise the antigens of bacterial meningitis as foreign so engulf the pathogen forming a phagosome. The lysosome of the macrophage fuses with the phagosome to form a phagolysosome. The lysosome then releases lysozymes which hydrolyse the pathogen. The bacterial meningitis antigens are then presented on the macrophage cell surface membrane. Macrophages present these antigens to T lymphocytes causing clonal selection of the T lymphocyte that recognises the antigen as foreign, then clonal expansion occurs by mitosis. This can form cytotoxic T cells and helper T cells. Helper T cells stimulate specific B lymphocytes resulting in clonal selection and expansion of the B lymphocyte forming plasma B cells and memory B cells. Plasma B cells produce complementary antibodies to the bacterial meningitis antigen. Once the pathogen is removed from the body the concentration of plasma B cells reduces leaving only memory B cells. Memory B cells provide immunological memory to the bacterial meningitis. Once the body encounters bacterial meningitis again these memory B cells can replicate and differentiate rapidly to form plasma B cells producing antibodies complementary to the bacterial meningitis antigen. Therefore, due to this rapid response symptoms can be prevented upon reinfection known as the secondary immune response.