A CONTEMPORARY VIEW OF TRANSPLANTATION TOLERANCE - AN IMMUNOLOGISTS PERSPECTIVE

The unique feature of the immune system is its capacity to distinguish between self and non-self components. The selectionists have postulat ed that deletion of clones during development could account for this p henomenon. The Bretscher/Cohn theory of self/non-self discrimination p rovided a model whereby self-reactive clones could be eliminated at an y stage of the animal's life. Experimental evidence demonstrates that clonal deletion can occur and is probably dependent on lymphohematopoi etic chimerism involving the passage of cells to the thymus. However, tolerance to peripheral tissue antigens that do not have direct access to the thymus is not maintained by deletional tolerance. In this situ ation an active process negatively regulates the response of the immun e system to non lymphoid, tissue-specific antigens.