When an antigen binds to a receptor on a T cell, the T cell becomes activated and differentiates into different types of T cells. What are these T cells and what are their functions? (6 marks)

There are three main types of T cell. T helper (CD4+), T killer (CD8+) and T memory. The CD4+/8+ are complex proteins on the surface of each respective T cell that they use in their function. T helper cells can either suppress or stimulate B cell differentiation into antibody-producing plasma cells. T killer cells recognise virus-infected cells, damaged cells or cancerous cells due to specific antigens that the "normal" cell will express on its cell surface membrane. T killer cells usually function to kill cells by activating a caspase enzyme pathway which leads to cell destruction. Finally, T memory cells are formed for post-infection, and they remember the specific antigen pattern of the pathogen. This means that, the next time the pathogen invades the body they can recognise the pathogen faster and thus induce a faster, and greater, immune response from the adaptive immune system.