The Role of Membrane Proteins in… IMMUNITY

What is an antigen? An ANTIGEN is anything that stimulates the production of antibodies by the immune system. Antigens are nametags on the outside of cells. So… what type of membrane protein are they?

Antigens can include… Pathogens – which are disease causing organisms such as viruses and bacteria Parts of pathogens Bacterial toxins Insect venom Pollen Transplanted tissue Incompatible red blood cells Many substances can be antigens or contain antigens.

WHITE BLOOD CELLS (WBCs) are the main cells of the immune system. These cells are very numerous; of the approximately 100 trillion cells in your body, 2 trillion are white blood cells. The two types essential to immunity are macrophages and lymphocytes. White blood cells detect invader antigens.

Macrophages have receptor proteins on their membranes that recognize a substance that is non-self by its antigens. Macrophages are the first line of defense. A macrophage engulfs the pathogen and displays the pathogen’s antigens on its cell membrane.

Millions of different types of lymphocytes can be made, each with unique receptors so that they can recognize different antigens. Lymphocytes are the second line of defense.

A macrophage then binds to a helper T cell which causes the release of a chemical called interleukin-1 (IL1) Macrophages stimulate helper T cell lymphocytes. This chemical activates more helper T cells which release a second chemical called interleukin-2 (IL2)

Interleukin-2 not only stimulates helper T cells to divide faster, it also stimulates the production of cytotoxic T cells (killer T cells) Killer T cells have receptor proteins that recognize infected body cells by the foreign antigens on their surface They kill the cell by poking a hole in the membrane. The infected cell’s cytoplasm leaks out and the cell dies. T cells and infected body cells are involved in the cell-mediated immune response.

Interleukin-2 also stimulates B cells that have complementary antibodies to the antigen to divide. B cells and antibodies are involved in the antibody-mediated immune response.

Memory B cells are the body’s long term protection against re- infection. B cells divide into memory B cells and plasma cells. The second time you are exposed to the pathogen, the memory cells recognize it and divide rapidly – producing many more antibodies. This eliminates the invader before it can cause illness.

Most of the B cells form plasma cells which are cells specialized to make antibodies (up to 30,000 per second for 4-5 days!). Plasma cells make antibodies. Antibodies prevent the pathogen from entering cells and cause the pathogens to clump so macrophages can engulf them - thereby stopping the spread of infection ANTIBODIES are Y-shaped molecules that bind to a specific antigen inactivating it

A VACCINE is a solution that contains dead or weakened pathogens or material from a pathogen. The antigens present in a vaccine will prompt the body to produce antibodies and memory B cells that will be available if the real pathogen enters the body. Vaccination is a term derived from the Latin vacca (cow) after the cowpox material used by Edward Jenner in the first vaccination. Vaccines imitate pathogens.