Cell Differentiation in Human Lymphoid Tissue

In the last two decades, anatomic compartmentalization of T and B cells within lymphoid tissues has been demonstrated in a wide variety of species, including man (1-5). T cells are located in the paracortical or interfollicular regions of lymph nodes and in the lymphoid tissues of the intestine and tonsil, whereas in the spleen, T cells are found primarily in the periarteriolar region of the Malpighian corpuscles. In contrast, the majority of B lymphocytes are found in lymphoid follicles. Until recently, studies in man have been severely limited by the lack of specific reagents to define T and B lymphocytes and their subpopulations. This situation has improved with the development of monoclonal antibodies against specific populations of lymphocytes. We have reported on studies using a panel of T cell-specific monoclonal antibodies in which the exact anatomic location in the human lymph node of subpopulations of T lymphocytes was determined (6). The present study was undertaken to investigate the distribution of B lymphocytes in various stages of differentiation within human lymphoid tissue. Lymphocytes of B cell origin have been shown to express a large number of cell surface determinants. Human B cell differentiation has been studied through the identification of several cell surface markers, including the heavy chain isotypes of immunoglobulin (7-8), HLA-D related Ia-antigens (9-10), receptors for the C3 component of complement (11, 12), receptors for the Fc portion of IgG (13, 14), and receptors for murine and monkey erythrocytes (15, 16). Although these markers have provided some insight into the sequence of B cell differentiation in man, their utility has been limited because they are also expressed on cells of other lineages. Recently, we have reported on the development and characterization of two monoclonal antibodies that define B cell-specific differentiation antigens (17-20). These antigens, termed B 1 and B2, have been shown to be distinct from previously described B cell surface determinants. Moreover, they are distinct from each other, as shown by their molecular weights and their restricted expression on normal and malignant B lymphocytes (17-20). In pokeweed mitogen-induced B cell differentiation, B2 and then B I antigens are sequentially lost from the B cell surface (19). In the present study, the cellular localization of the B cell-specific antigens, B 1 and