Phagocytes, lymphocytes and antibodies

Last time

Before we start: last time, in Pathogens and how infectious diseases are transmitted, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

The body's security team

Every day your body meets thousands of microbes. Almost none of them make you ill, because a team of cells recognises them and removes them. Some of the team eat invaders on sight, and some build a tailor made weapon, the antibody. Telling the cells apart, and the antibody structure, is where the marks are.

Antigens, self and non-self

An antigen is a molecule, usually a protein or glycoprotein, that triggers an immune response. Antigens are found on the surfaces of pathogens, and in toxins. The immune system learns to ignore self antigens, which are on the body's own cells. It attacks non self antigens, from pathogens, from transplanted cells, and from cancer cells. A glycoprotein on the surface of one of your own macrophages is a self antigen. A viral capsid protein is not.

Phagocytes

Phagocytes are white blood cells that engulf pathogens by phagocytosis. Neutrophils are the most common and are first to arrive at an infection. Monocytes are phagocytes that leave the blood and become macrophages in the tissues. Macrophages engulf pathogens, digest them in lysosomes, and display the antigens on their surface. Phagocytosis is non specific. The phagocyte recognises that something is foreign, but does not need to know which pathogen it is.