Davine Opstelten

Germinal centers and the B-cell system

SummaryThe migration pattern of germinal center cells of the rabbit appendix was studied and compared with that of appendix dome cells, spleen cells, thymus cells and thoracic duct lymphocytes. To discriminate T-and B-cell migration pathways, normal or T-cell-depleted rabbits were used as donors. Cell suspensions were labeled in vitro with 3H-leucine followed by intravenous transfer. The migration of labeled cells in lymphoid organs was studied using autoradiography, particular attention being paid to the spleen of the recipient. B-cells from the appendix dome, spleen and thoracic-duct lymph migrate to primary follicles or the corona of secondary follicles via thymus-dependent areas of peripheral lymphoid organs. In contrast, a B-cell subpopulation from the germinal centers of the appendix migrates to the center of splenic primary follicles and into germinal centers. The migration of germinal center cells to splenic follicle centers is not enhanced by specific antigens. The migration properties of B-cells, possibly changing during differentiation, may be instrumental in the two types of immune reactions, i.e., plasma-cell reaction and germinal-center reaction.

In Vivo Regulation of B Lymphocyte Production in the Bone Marrow: Effects and Mechanism of Action of Exogenous Stimuli on Pre-B Cell Proliferation and Lymphocyte Turnover

The present studies demonstrate that a single administration of an extrinsic agent (SRBC) can stimulate increased production of B lymphocytes in mouse bone marrow as revealed by 2 in vivo assays which quantitate pre-B cell proliferation and small lymphocyte renewal, respectively. The mechanisms mediating this stimulatory effect are sensitive to silica in vivo and require the presence of the spleen. Early events are both silica-sensitive and spleen-dependent, while a subsequent stage appears still to be spleen-dependent but not silica-sensitive. Sustained exogenous stimulation by multiple SRBC injections for 4 wk in young mice produces an expanded population size and increased production of pre-B cells and B lymphocytes in the bone marrow, apparently an elevated kinetic steady state of B lymphocyte production. (Formula: see text). As depicted schematically in Figure 1, the results suggest that the magnitude of bone marrow B lymphocyte production in vivo may reflect a basal level, putatively regulated by microenvironmental and other endogenous factors, which is amplified by exogenous environmental stimuli mediated by the action of macrophages located in the spleen. Further questions about such an environmental amplification (Fig. 1) concern the nature of later events in the spleen, the identity of putative stimulatory factors or cells circulating from the spleen to the bone marrow, the receptive target cell stages in the bone marrow and the consequences of this process with respect to the size and diversity of B lymphocyte clones and of primary humoral immune responses in vivo.

Homing of germinal-center cells into germinal centers of lymph node via afferent lymphatics

SummaryAffinity of lymphoid cells for the microenvironment of germinal centers (GC), as detectable in transfer experiments by rapid homing in spleen GC from the blood, is a capacity expressed by only a subset of lymphoid cells, in particular by those constituting a GC. However, when introduced into the blood stream, these cells do not home into GC of lymph nodes and gut-associated lymphoid tissues. To investigate further this homing inability for high endothelial venule (HEV)-containing lymphoid tissues, GC cells isolated from donor rabbit appendix were labeled in vitro with 3H-leucine and injected into an afferent lymph vessel of recipient popliteal lymph nodes. Draining lymph nodes were removed 15 min to 24 h after cell administration and prepared for radioautography. For reference, the migration of cells isolated from Peyers patches and thoracic duct lymph was also studied. By use of appendix GC cells, large numbers of labeled cells were found to migrate into GCs of the outer cortex centripetally, i.e., from the subcapsular sinus through the lymphocyte corona into the GC proper. The same was observed for cells from Peyers patches, although in smaller numbers. Thoracic duct lymphocytes were only localized in the lymphocyte corona and the deep cortex. Thus, appendix GC cells and a subpopulation of cells from Peyers patches can reach lymph node GC, but only when administered intralymphatically. We conclude that cells expressing affinity for the GC microenvironment do so for both spleen and lymph node GC, but do not have the capacity to interact with the wall of HEV; its implication for the understanding of the dynamics of a GC reaction is discussed.

B Cell Precursor Populations in Fetal and Neonatal Rat Liver: Frequency, Topography and Antigenic Phenotype

In rodents and man B lymphocyte development starts in fetal liver, and gradually shifts to the bone marrow where it is maintained throughout life (1). The immediate precursors of newly formed surface IgM bearing B cells are pre-B cells defined by the presence of μ heavy chains (but not light chains) in the cytoplasm only (1).

Pattern of Distribution of Early B Lineage Cells in Rat Bone Marrow

In mammals bone marrow (BM) is the primary site of B lymphocyte genesis in postnatal life, providing precursors for antibody forming cells for humoral immune responses. The B progenitor cells are situated in the BM within a three dimensional network formed by stromal cells, vascular elements and erythroid, myeloid and lymphoid cells. Little is known about their spatial organisation.

Rat Immunoglobulin Genes have Comparable Patterns of JH Rearrangement in Normal Peripheral B Cells and In Pre-B And Cultured TdT+ Cells from Bone Marrow

Pre-B cells from normal rat bone marrow were isolated by first rosette-depleting granulocytes, T cells and stem cells with W3/13 mAb and mature B cells with anti-Ig mAb, and then in some samples enriching by FACS-sorting HIS24+ cells. Presumptive precursors of these pre-B cells possessing terminal deoxy-nucleotidyl transferase were prepared by culture of normal marrow. The extent of rearrangement of kappa and heavy chain genes was estimated on both these types of cells and on mature peripheral B cells by measuring the disappearance of the germ-line restriction fragments encoding J segments (other than JH1) relative to a non-rearranging CK fragment. Pre-B cells and B cells showed similar degrees of rearrangement of their kappa genes, leaving roughly half in germ-line form; the TdT+-enriched cells showed approximately similar heavy chain rearrangement as the peripheral B cells. Some non-germ-line restriction fragments hybridising with JH in sufficient amount to register as discrete bands on Southern blots were found in common between these different cell populations taken from different individual donors. These may represent preferred D-JH or perhaps V-D-JH rearrangement arising repetitively in independent clones, or may be due to dominance by a few preferred clones.