The essential difference between humoral and cellular responses as shown by B cells and T cells. The role of plasma cells and memory cells in producing a secondary response.

Lymphocytes are white blood cells. They are created as stem cells in the bone marrow. They have defences that are specific to the pathogen they are attacking (unlike phagocytes which do the same for everything) which makes response slower, but more effective long term.

B cells

• mature in the bone marrow
• respond to antigens in the bodies fluids: tissue fluid; blood (humoral response)
• produce antibodies
• produce memory cells

1. ingest pathogen and present antigens on the surface
2. these are recognised by helper T cells, which stimulate mitosis
3. plasma cells and a Memory cells are produced
4. plasma cells secrete antibodies which attach to antigens on a pathogen to destroy it (primary response)
5. memory cells stay in the blood stream for many years, if they encounter the same pathogen again, they can divide rapidly and with greater intensity to make plasma cells which will make antibodies (secondary response)

The secondary response provides long term protection as they memory cells stay alive for many years. They produce many more plasma cells and are much faster at doing so than the primary response, this means that the pathogen can be fought before it causes harm to the body.

T cells

• mature in the thymus glands
• recognise antigens if presented on the surface of other cells (cell-mediated response)
• stimulate b cells and phagocytes
• kill infected cells
• produce memory cells

1. Phagocytes, infected cells and cancer cells all display antigens on their surface
2. A specific helper T cell will have receptors that fit exactly with the antigens- when they meet, the helper T cell stimulates other T cells to form appropriate clones by mitosis
3. These T cells can: stimulate B cells; stimulate phagocytes; develop into memory cells; kill cells
4. They kill cells by producing a protein which breaks cell-surface membranes.