Differentiation and Ontogeny of Lymphoid Cells

Abstract

For many years it has been recognised that lymphocytes play a central role in the initiation and development of both cellular and humoral immunity. In considering the heterogeneous nature of specific immune responses it was proposed from studies in birds¹ that there were two distinct lymphoid cell differentiation pathways, in that the bursa of Fabricius controlled the development of cells of the antibody forming series, whereas the thymus controlled the differentiation of lymphoid cells involved in cellular immunity. With the subsequent development of the concept of cell interactions in immune responses^{2, 3} the specific roles of bone marrow derived cells, (termed B cells, implying either bursal equivalent derivation) and T cells, in production of antibody were clearly defined. The subsequent application of a variety of cell surface markers and receptors to the analysis of distinct populations of lymphoid cells has even further validated the concept of two broad streams of lymphocyte differentiation represented under the general groupings of T and B lymphocytes. In this presentation I would like to concentrate on several of the current problems relating to the differentiation and ontogeny of T and B lymphocytes.