Introductory remarks

Abstract

1. My introductory remarks on this occasion will be of a very general kind, and I hope that immunologists and pathologists will forgive me if much of what I say is familiar or even trite. My plan is, first, to define the concept of ‘immunological tolerance’ as it will be used by later speakers; then to consider the immunological systems to which the concept may apply; then, thirdly, to attempt to differentiate tolerance from other forms of inhibition of the immune response; and, finally, to discuss a number of its biological implications. When adult animals are confronted with antigenic substances they undertake some kind of immunological response. The antigenic substances may be erythrocytes or living tissue cells, micro-organisms, or foreign proteins or polysaccharides; under conditions which I shall describe later, they may even be constituents of the responding subject’s own body. The immunological responses include antibody formation and its sequelae; a hypersensitivity often associated with local inflammation; or protective reactions of a kind not yet fully understood. So much is true of adults. When embryos or very young animals are exposed to antigenic stimuli, nothing of the kind occurs, and for many years it was believed that nothing out of the ordinary occurred at all. The truth is quite otherwise. When an embryo is confronted with an antigenic substance it may be so affected that, when it grows up, its power to respond to that antigen is weakened, altered in kind, or totally suppressed. The state of specific immunological inactivity so produced has been defined as tolerance ,* and most of you here will know, or know of, the brilliant train of reasoning which led Burnet and Fenner to predict the existence of the phenomenon on a priori grounds.