Читать книгу Immunology - Richard Coico - Страница 55

It has been estimated that in a naïve (nonimmunized) animal, only one in every 10³–10⁵ lymphocytes is capable of recognizing a typical antigen. Therefore, the probability that an antigen will encounter these cells is very low. The problem is compounded by the fact that for synthesis of antibody to ensue, two different kinds of lymphocytes—the T lymphocyte and B lymphocyte, each with specificity against this particular antigen—must interact.

Statistically, the chances for the interaction of specific T lymphocytes with their particular antigen, and then with B lymphocytes specific for the same antigen, are very low. However, nature has devised an ingenious mechanism for bringing these cells into contact with antigen. The antigen is carried via the draining lymphatics to the secondary lymphoid organs, where the antigen is exposed on the surface of fixed specialized cells. Because both T and B lymphocytes circulate at a rather rapid rate, making the rounds every several days, some circulating lymphocytes with specificity for the particular antigen should pass by the antigen within a relatively short time. When these lymphocytes encounter the antigen for which they are specific, the lymphocytes become activated and the adaptive immune response, with specificity against this antigen, is triggered.