The immune response, vaccination and monoclonal antibodies

Last time

Before we start: last time, in Phagocytes, lymphocytes and antibodies, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Remembering an enemy

The first time you meet a virus, you get ill for days. The second time, you may not notice at all. Your body has remembered the invader. That memory is what vaccines borrow, and it is also what scientists exploit to make antibodies in the laboratory.

The primary response

An antigen on the pathogen is displayed by a macrophage. A T helper cell with a complementary receptor binds to it, and is activated. The T helper cell releases cytokines, which stimulate B cells with the matching receptor to divide, in clonal selection and expansion. Most B cells become plasma cells and secrete antibodies. Some become memory cells. This takes several days, so antibody levels rise slowly and stay low.

The secondary response

Memory B cells and memory T cells survive for years. On a second infection with the same antigen, they recognise it at once. They divide rapidly and make plasma cells straight away, so antibodies appear within hours or a day or two, in larger amounts, and last longer. The pathogen is destroyed before symptoms appear. This is immunological memory.