Thymic lymphocyte differentiation and thymic leukemogenesis

Abstract

Henry Kaplan helped establish the fields of lymphocyte biology and viral leukemogenesis by his early and continuing studies on radiation leukemogenesis. As one of Henry's students I carried on these dual preoccupations with thymic lymphocytopoiesis and thymic lymphomagenesis. This communication demonstrates that 1) thymic lymphocytes are derived from bone marrow precursors which lack any T cell markers; 2) these bone marrow cells (or their clonogenic subsets) can give rise to either thymic cortical plus medullary progeny, or medullary progeny alone; 3) thymic lymphocytes mature in contact with 3–5 classes of nonlymphoid cells (thymic nurse cells, cortical dendritic epithelial cells, medullary epithelial cells, dendritic reticular cells, and macrophages), and one of these subsets, cortical dendritic epithelial cells, express an unusual distribution of MHC antigen (perhaps utilized in the maturation of T cell MHC restriction); 4) the population of cells which are poised to emigrate from the thymus are a unique subset of cortical cells which possess peripheral lymphoid organ homing receptors; and 5) the thymic target cells for retrovirus lymphomagenesis express highly specific retrovirus receptors that are analogous (and perhaps synonymous) with antigen-specific T cell receptors.