Lymphocyte

Lymphocytes produce antibodies. An antibody has a shape complementary to a particular antigen on a pathogen, so it binds specifically and helps bring about the pathogen's destruction.

HIV reduces the number of lymphocytes, which are white blood cells involved in immune defence. As lymphocyte numbers fall, the body becomes less able to fight infections. The person is then more susceptible to opportunistic infections, such as pneumonia, caused by pathogens that take advantage of the weakened immune system.

Lymphocytes are another type of white blood cell. They make antibodies, proteins that bind to particular markers called antigens on pathogens. Binding can help other white blood cells recognise the pathogens; lymphocytes can also make antitoxins that neutralise toxins released by pathogens.

Antibodies are proteins made by lymphocytes, a type of white blood cell. The shape of an antibody's binding site is complementary to a particular antigen, so the antibody can bind to that antigen.