Control of the immune response

When foreign substances (macromolecules, bacterias or viruses, to be further called antigens and abbreviated as Ag) attempt to invade our body, a strong reaction, specific of the antigen, is triggered (we shall not describe here the mecanisms that are not specific of the Ag). The so-called immune reaction consist in the secretion of macromolecules (the antibodies abbreviated as Ab) and cells in the blood and the lymph (the lymphocytes) which participate in the recognition and the destruction of the antigens. Recognition is the process by which a site of the surface of an antigen is fixed by the specific site of an immunoglobulin (an Ab) or the receptor on the membrane of a lymphocyte. Specificity is ensured by the steric complementarity of the van der Wals link. The transformation of the Ab or of the cell receptor gives then rise to a series of cellular transformations, secretions, and multiplication which result in the subsequent destruction of the foreign antibodies. At the very simple level of our description, all what we say about one mechanism, wether molecular with Ab or cellular with lymphocyte, is valid for the other one and we shall not distinguish further between the two immune responses.