Antibody repertoire development in fetal and neonatal piglets. VI. B cell lymphogenesis occurs at multiple sites with differences in the frequency of in-frame rearrangements

Characterization of porcine CD19 and anti-CD19 monoclonal antibodies

CD19 is an important pan B cell marker and co-stimulatory protein in humans and mice. Efforts to further characterize B cell ontogeny in swine have been hampered by the lack of monoclonal antibodies (mAb) to valuable surface markers like Vpre-B, CD19, CD34 and CD43. We report here on the complete nucleotide and deduced amino acid sequence of porcine CD19, the cross-reactivity of anti-human CD19 monoclonals and efforts to prepare anti-porcine CD19 mAb to bacterially-expressed products. Porcine CD19 is highly homologous to those in the few other species studied, i.e. human, mouse and guinea pig, but only in certain domains. Among the 14 CD19 exons, homology approaches 90% to human CD19 in exons 6, 9, 11 and 12 and is approximately 80% with other species in this region. The highly homologous C-terminal cytoplasmic region contains nine tyrosines including the YEND/E motif that binds the SH2 domain of Fyn. Two different porcine CD19 isoforms that differ in their 3' UTRs were identified just as in human CD19. Thus, the signaling properties of CD19 may be similar to those in humans. On the other hand, only 60% sequence similarity was seen in exons 1-5 that encode the N-terminal extracellullar region that is involved in ligand binding and is the target of CD19-specific mAb. This probably explains why only 1 of the 17 anti-human CD19 mAb tested recognized swine B cells. Furthermore, when the extracellular domains of CD19 were expressed in E. coli, mAbs to the bacterially-expressed product did not recognize CD19 on porcine B cells suggesting that carbohydrate-dependent conformation may determine antigenicity.

Biases in Ig lambda light chain rearrangements in human intestinal plasma cells

Human intestinal lamina propria plasma cells are considered to be the progeny of chronically stimulated germinal centers located in organized gut-associated lymphoid tissues such as Peyer's patches and isolated lymphoid follicles. We have sampled human colonic lamina propria plasma cells and naive and memory B cell subsets from human Peyer's patches by microdissection of immunohistochemically stained tissue sections and used PCR methods and sequence analysis to compare IgVlambdaJlambda rearrangements in the plasma cell and B cell populations. Rearrangements that were either in-frame or out-of-frame between V and J were compared. Usage of IgVlambda families in the in-frame rearrangements from the plasma cells resembled that observed in the mantle cells, suggesting that antigenic selection for cellular specificity does not dramatically favor any particular Vlambda segment. However, in marked contrast, out-of-frame rearrangements involving Vlambda1 and Vlambda2 families are rarely observed in intestinal plasma cells, whereas rearrangements involving Vlambda5 are increased. This resulted in significantly biased ratios of in-frame:out-of-frame rearrangements in these Vlambda families. Out-of-frame rearrangements of IgVlambdaJlambda from plasma cells, including those involving the Vlambda5 family, have a significant tendency not to involve Jlambda1, consistent with the hypothesis that this population includes rearrangements generated by secondary recombination events. We propose that modification of out-of-frame rearrangements of IgVlambdaJlambda exists, probably a consequence of secondary rearrangements. This may be a mechanism to avoid translocations to susceptible out-of-frame IgVlambdaJlambda rearrangements during somatic hypermutation.

Terminal deoxynucleotidyl transferases from elasmobranchs reveal structural conservation within vertebrates

The DNA polymerase (pol) X family is an ancient group of enzymes that function in DNA replication and repair (pol beta), translesion synthesis (pol lambda and pol micro) and terminal addition of non-templated nucleotides. This latter terminal deoxynucleotidyl transferase (TdT) activity performs the unique function of providing diversity at coding joins of immunoglobulin and T-cell receptor genes. The first isolated full-length TdT genes from shark and skate are reported here. Comparisons with the three-dimensional structure of mouse TdT indicate structural similarity with elasmobranch orthologues that supports both a template-independent mode of replication and a lack of strong nucleotide bias. The vertebrate TdTs appear more closely related to pol micro and fungal polymerases than to pol lambda and pol beta. Thus, unlike other molecules of adaptive immunity, TdT is a member of an ancient gene family with a clear gene phylogeny and a high degree of similarity, which implies the existence of TdT ancestors in jawless fishes and invertebrates.