Genetic aspects of cellular interactions in the immune response.

Our understanding of the complex cellular interactions responsible for mediating effective immune responses has increased substantially in recent years. It is now clear that the genetic loci that control the interaction of the cells of the immune response encode groups of closely related cell-surface molecules. These molecules are the class I and class II antigens of the MHC, the differentiation antigens on lymphocyte subpopulations, and the receptors of various types, including the membrane immunoglobulin of B lymphocytes and the antigen receptors of T lymphocytes. Biochemical analysis of these cell surface molecules has demonstrated that they display important DNA sequence homologies. A polypeptide of approximately 110 amino acids comprises the basic building block for many of the cell surface molecules. Gradually, as a consequence of evolutionary development, the immune system has expanded its ability to respond to the external environment by an increased complexity of lymphocyte subpopulations and the surface structures that modulate their interaction. These cell surface molecules provide the structures that allow collaborative interaction of different cell types and that form the multiprotein receptor complexes involved in the recognition of, and specific response to, foreign antigens. Our future understanding of the control of the immune response will depend upon establishing the biochemical nature and the multifaceted interactions of these important molecules.