This symposium was established in 1976 for the purpose of bringing together once every two or three years, active investigators in the forefront of contemporary immunology, to present their findings and to discuss their significance in the light of current concepts and to identify important new directions of investigation. The founding of the symposium was stimulated by the achievement of major breakthroughs in the understanding of the immune recognition of proteins and peptides. We believed that these breakthroughs will lead to the creation of a new generation of peptides which should have enormous potential in biological, therapeutic and basic applications. This anticipated explosion has finally occurred and many applications of these peptides are now being realized.

The main symposia topics of the fourth symposium were: T-cell recognition of proteins, structure and function of the T-cell receptor, presentation of protein antigens, recycling and activation of membrane receptor molecules, Ir-gene control of T-cell response and methods of cell separation. The molecular features recognized by antibodies on proteins were the first immune recognition sites to be localized. Many of these molecules are discussed in this volume. The diversity of antibody specificity occupied center stage in immunology for over three decades. The diversity in T-cell specificity and its understanding in molecular terms had to await the advent of the recent powerful tools of molecular biology. In this volume, the structure of the T-cell receptor and its relationship to immune recognition by t cells are discussed.

Having acquired a great deal of knowledge about protein molecular features that are recognized by antibodies and by T-cells, it has become feasible, using precise molecular tools to investigate the first phases of recognition by the immune system. For a long time, it has been believed, and many experiments were so designed to show, that the first critical steps of immune recognition involved internalization and degredation of the protein by the antigen-presenting cells which then present these fragments to the 5-cells. Thus, the fragments constitute the target of recognition. However, in the last 5-6 years, a small, greatly outnumbered group of investigators have reported studies that would suggest that the accessory cells present protein antigen in intact form to the T-cell. In other words presentation is independent of processing. In this volume, proponents of both schools of thought present some of their findings and viewpoints.

It has also been suggested recently that antigen presentation may not be entirely unrelated to other membrane-mediated cellular activation phenomena. The resemblance, if any, of these systems to immune recognition is, therefore, examined, and the latest concepts of recycling and activation of membrane receptor molecules are discussed in this volume. The interaction of cells and molecules which generate an immune response are controlled and regulated at various steps in the pathway. Manipulation and therapeutic exploitation of the immune system cannot be obtained without detailed understanding of these intricate networks of recognition and regulation. Some of the molecules that control and regulate the immune system are discussed in this volume. Cellular studies in immunology are highly dependent on the ability to isolate the appropriate cell lines and colons. The procedures presently employed have been quite effective. But yet new and promising technologies are emerging.

The ability to perform cell separations in microgravity may prove to the one of the most important biologically-related fringe benefit of the space program. The current status of these investigations in reviewed.