CD5+ and CD5- B1-like lymphocytes in healthy guinea pig

Developmental expression of B cell molecules in equine lymphoid tissues

Identification and classification of B cell subpopulations has been shown to be challenging and inconsistent among different species. Our study tested aspects of ontogeny, phenotype, tissue distribution, and function of equine CD5^hi B cells, which represented a greater proportion of B cells early in development and in the peritoneal cavity. CD5^hi and CD5^lo B cells differentially expressed B cell markers (CD2, CD21, IgM) measured using flow cytometry, but similar mRNA expression of signature genes (DGKA, FGL2, PAX5, IGHM, IL10) measured using quantitative RT-PCR. Sequencing lambda light chain segments revealed that CD5^hi B cells generated diverse immunoglobulin repertoires, and more frequently bound to fluorescence-labeled phosphorylcholine. This study shows developmental characteristics and tissue distribution of a newly described subpopulation of B cells in the horse.

Assessment of snapper (Pagrus auratus) natural IgM binding to bromelain treated sheep erythrocytes

Normal snapper (Pagrus auratus Bloch and Schneider) serum was examined for natural IgM that binds to protease (bromelain) treated sheep erythrocytes (BrSRBC) in a model assay system that has been used to appraise natural IgM of various mammals. Normal snapper serum lysed BrSRBC while haemolysis was abrogated by heat inactivation of serum and in divalent cation-deficient conditions, indicative of classical complement mediated lysis. In addition, heat inactivated normal snapper serum agglutinated BrSRBC while phosphatidylcholine (PtC) liposomes partially inhibited both haemolysis and agglutination. Inhibition of haemolysis and agglutination may have been mediated by an interaction between immunoglobulin (Ig) and PtC as protein A purified snapper Ig bound to PtC liposomes. However it is not known if this binding was PtC specific nor if the binding was initiated by either the Fab and/or Fc domains of snapper Ig. BrSRBC plaque forming cells (PFC) were detected in the peritoneal cavity, spleen, head kidney and peripheral blood of normal snapper. The greatest proportion of BrSRBC PFC per B cell was within the peritoneal cavity followed by the spleen, peripheral blood and head kidney. Together, these data suggest that normal snapper serum may contain natural Ig that binds BrSRBC, activating the classical complement cascade.

CD5 B cells and B-cell malignancies

Over the past year, progress has been made in understanding of the physiology and disease associations of CD5+ (B1) B cells, although their exact role in pathogenesis remains unclear. Earlier studies on the negative function of CD5 within the B-cell receptor complex have been substantiated, and it seems likely that soon the signaling pathways used by this coreceptor will be elucidated. Progress in diagnosis, physiology, and etiopathogenesis of CD5+ malignancies has been made, particularly in B-cell chronic lymphocytic leukemia. The low-level expression of surface immunoglobulin has been explained by the mutations that occur in the associated CD79b. Two new potential tumor-suppressor genes have been identified in the hot spot of chromosome 13q, which provides an exciting step forward in understanding of the etiopathogenesis of some B-cell chronic lymphocytic leukemia. Activated signal transducers for activation of transcription factors molecules have been shown to be phosphorylated on different amino acids in B1 and chronic lymphocytic leukemia tumors, although the significance of this is, as yet, unclear. Finally, aberrant expression of CD40L by chronic lymphocytic leukemia T cells may contribute to the immunodeficiency that develops in these patients.