The immune system avails the organism forfend itself from pathogens, such as peregrine particles, molecules, and cells. To do this, it must be able to distinguish between self and peregrine matter; it must be able to learn to agnize incipient pathogens and to recollect them subsequently. It must additionally be able to eliminate the invading organism. The term ‘antigen’ is utilized to refer to peregrine molecules that can arouse an immune replication; ‘antibodies’ refer to sundry types of protein that form this replication in the immune system (mnemonic: the antigen engenders the antibody replication). Many types of antibodies are made in the bone marrow, of which we may fixate on three. These circulate in the blood stream as white blood cells and develop through a number of stages.

1. Granulocytes (AKA polymorphous leukocytes). These include neutrophils, basophils and eosinophils, and their tasks include engendering the inflammatory replication which is designed to dissever the site of infection from circumventing tissue, and withal to ingest peregrine material (a process called phagocytosis).

2. The second group of cells, macrophages and monocytes, withal undertake phagocytosis, but withal process antigens for subsequent processing by the lymphocytes.

3. The final group, lymphocytes, comprises T-lymphocytes (made in the thymus), and B-lymphocytes. Both of these are involved in storing immune recollection, so that antigens once encountered can be recollected subsequently and a replication to them mounted more expeditiously. This recollection is categorical for each type of antigen and comprises our acquired immunity; vaccinations capitalize on this. T-lymphocytes are additionally involved in cytotoxicity and in regulating the immune replication: there are T-auxiliaries and T-suppressors. Some T cells are additionally toxic to peregrine cells. The B-lymphocytes are involved in engendering antibodies called immunoglobulins (abbreviated Ig) which are proteins capable of assailing peregrine material.