Migration of Newly-Produced Virgin B Cells from Bone Marrow to Secondary Lymphoid Organs

Abstract

If marked B cells from thoracic duct lymph are transferred to syngeneic recipients they characteristically migrate via high endothelial venules or marginal zone blood sinusoids to the follicles of secondary lymphoid organs (1,2). Less is known of the capacity of virgin B cells, recently produced in the bone marrow, to migrate to secondary lymphoid organs. Under normal conditions the rate of primary B lymphopoiesis greatly exceeds the rate at which B cells are lost from the peripheral B cell pool (3). It follows that most newly-produced virgin B cells can only have a short life span. We have identified two pathways by which newly-produced virgin B cells are recruited to the peripheral pool. One appears to be antigen-independent and recruits B cells in sufficient numbers to replenish loss from the peripheral pool (4,5). If the peripheral pool is depleted selectively by cytotoxic agents a high proportion of the bone marrow output is recruited until the peripheral pool is replenished. The second mechanism resulting in virgin B cell recruitment appears to be antigen-dependent. In this situation newly produced virgin B cells are activated by T cell-dependent antigens and the memory B cells generated may become part of the peripheral pool. This process appears to occur only in periods immediately following exposure to antigen (6). The established phase of T cell-dependent responses seems to be maintained by sequential cycles of memory B cell activation with little new virgin B cell recruitment (3,5,6).