ABSTRACT
The duration of tolerance is much greater in T cells, which is 150 d, compared with that in B cells, which is only 50 to 60 d. T suppressor cells are also very important in maintaining natural tolerance to self antigens. For example, they may suppress T helper cell activity. Maintenance of tolerance is considered to require the continued presence of specific antigens. Low antigen doses may be effective in inducing tolerance in immature B cells leading to clonal abortion, whereas T cell tolerance does not depend upon the level of maturation. Another mechanism of B cell tolerance is cloning exhaustion, in which the immunogen activates all of the B lymphocytes specific for it. This leads to maturation of cells and transient antibody synthesis, thereby exhausting and diluting the B cell response. Antibody-forming cell blockade is another mechanism of B cell tolerance. Antibody-expressing B cells are coated with excess antigen, rendering them unresponsive to the antigen.
