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In non-specifically immunized rats, bred under conventional conditions, the first ‘spontaneous’ germinal centres were observed by 21 days after birth. Deliberate antigenic stimulation led to an earlier appearance of germinal centres in neonatal spleen: immunization with sheep red blood cells as early as 7 days after birth resulted in germinal centre formation in the spleen as observed 7 days later. By that time the first primary follicles could also be observed, in both immunized and non-immunized rats. Although 3-day-old rats upon antigenic stimulation failed to generate germinal centres in their spleen, transfer experiments of 3-day-old spleen cells to lethally X-irradiated syngeneic adult recipients indicated that 3-day-old spleens at least contained all the essential lymphoid elements (B and T cells) needed for germinal centre formation. These results strongly suggest that the failure to induce germinal centres in 3-day-old rats is most probably due to an immaturity of their splenic microenvironment. Immunohistochemical staining of frozen sections of neonatal rat spleen using mAb ED 5 and MRC OX-2 showed that follicular dendritic cells (FDC) were found as soon as primary follicles were found (i.e. by 14 days after birth). The appearance of FDC in neonatal spleens was not influenced by deliberate antigenic stimulation nor by the administration of adult spleen cells. We postulate that, during the development of FDC, a splenic microenvironment is created that allows primary follicle formation and the generation of germinal centres. [ABSTRACT FROM AUTHOR]

Using horse-radish peroxidase (HRP)-anti-HRP immune complexes, ‘antigen trapping’ was studied in the spleen of the turtle, Chrysemys scripta elegans. It was found that antigen-trapping cells were situated in the periellipsoidal lymphocyte sheath of the white pulp only. The antigen-trapping cells have a dendritic character and a large lobulated nucleus. Carbon injections revealed that these cells do not phagocytose. The results are discussed with respect to the phylogeny of antigen-trapping cells. [ABSTRACT FROM AUTHOR]

Haemopoietic cells carry a variety of cell-surface molecules, some of which are known lo have allotypic variation. In rats, the RT7 alloantigenic system has been well documented using alloantisera. We have produced the first mouse hybridoma cell line secreting an antibody. HIS41, which binds to leucocytes of rat strains carrying the RT7.2 but not the RT7.1 determinant. An IgG2b isotype switch variant (HIS4l.2b) of the original HIS41 (IgG1 isotype) was also made. HIS41 showed a clear and discrete binding in immunofluorescent and histological experiments and has already been used in several studies on haemopoietic cell turnover and differentiation employing PVG rats congenic for RT7. The present study addresses the question of whether the RT7 gene products are members of the L-CA family, which has been a matter of controversy over the last decade. When using HIS41 for the analysis of tissue distribution and molecular weight of RT7 gene products, a strong similarity was evident with the data reported for the L-CA detected by MRCOX-1 and MRCOX-30. These two MoAb have been reported to bind to all members of the L-CA family. All haemopoietic cells, excluding erythrocytes and the more mature stages of erythropoiesis, stained with HIS41. The molecular weights of HIS41 binding molecules on thymocytes and peripheral T cells were comparable to the L-CA precipitated by MRC OX-1. Capping and sequential immunoprecipitation studies indicated that HIS41 and MRC OX-30- binding molecules were identical. MRC OX-1, however, appeared to bind only a subset of these molecules. Thus, our study confirms the identity of RT7.2 gene products and L-CA. It also revealed a difference between MRC OX-1 and MRC OX-30 not noticed previously. [ABSTRACT FROM AUTHOR]

Recently, a cDNA encoding a newly identified rat antigen (HIS50 Ag) that binds to monoclonal antibody (mAb) HIS50 was cloned and shown to be homologous to cDNA encoding murine heat-stable antigen (HSA) and human CD24. Here we show that, like CD24 and HSA, at least part of HIS50 Ag is inserted into the plasma membrane by a glycosyiphosphatidylinositol (GPI)-lipid linkage and we describe its expression in rat haemolymphopoietic tissues. HIS50 Ag expression was almost exclusively confined to B lymphoid cells, the vast majority of T lymphoid cells, erythroid and myeloid cells were HIS50 -. Cell suspension analysis indicated that in bone marrow (SM) almost all Thy-1 + cells, H1S24 + cells [H1S24 recognizes the B-cell form of leucocyte common antigen (LCA)], terminal deoxynucleotidyl transferase-positive (TdT +) cells and (c + s)κ + cells expressed HIS50 Ag, and all (c+s)μ+ cells. A presumably early population of B lymphoid cells, expressing HIS24 Ag without HIS50 Ag, TdT or immunoglobulin (HIS24+HIS50- TdT- Ig-), constituted 1 .6% of BM nucleated cells. In blood, one-fifth of mononuclear cells were HIS50+, and about 85% of these expressed μ and/or κ chains. In spleen, flow cytometry analysis and immunohistology demonstrated heterogeneous expression of HIS5O Ag: immunoglobulin M (IgM)bright cells (as found largely in red pulp and marginal zone) were HIS50bright, while IgMdull cells expressed low or undetectable levels of HIS 50 Ag. Germinal centre B cells expressed high levels of HIS50 Ag. Germinal centres of lymph nodes and tonsil of man also bound HIS50. We conclude that HIS50 Ag expression in the haemolymphopoietic system of rat is virtually restricted to the B lineage. [ABSTRACT FROM AUTHOR]