Early Postnatal B Cell Ontogeny and Antibody Repertoire Maturation in the Opossum, Monodelphis domestica

Abstract

Marsupials are a lineage of mammals noted for giving birth to highly altricial young, which complete much of their “fetal” development externally attached to a teat. Postnatal B cell ontogeny and diversity was investigated in a model marsupial species, the gray short-tailed opossum, Monodelphis domestica. The results support the initiation of B cell development late in gestation and progressing into the first two weeks of postnatal life. Transcription of CD79a and CD79b was detected in embryonic tissue prior to birth, while immunoglobulin heavy chain locus transcription was not detected until the first postnatal 24 hours. Transcription of the Ig light chains was not detected until postnatal day 7 at the earliest. The predicted timing of the earliest appearance of mature B cells and completion of gene rearrangements is consistent with previous analyses on the timing of endogenous antibody responses in newborn marsupials. The diversity of early B cell IgH chains is limited, as has been seen in fetal humans and mice, but lacks bias in the gene segments used to encode the variable domains. Newborn light chain diversity is, from the start, comparable to that of the adult, consistent with an earlier hypothesis that light chains contribute extensively to antibody diversity in this species.

On the prenatal initiation of T cell development in the opossum Monodelphis domestica

“…Previous analyses on the initiation of B cell development in the opossum were consistent with it being delayed relative to T cells (Wang et al 2012a,b). However, transcription of the genes encoding the B cell receptor associated molecules CD79a and CD79b was found in late stage embryos (Wang et al 2012b).…”

“…Furthermore, cell surface expression of CD79b is not evident in embryos in spite a prior report of CD79b transcripts being detected prenatally in the developing opossum (Wang et al 2012b). This is consistent with IgH gene rearrangement not having begun and B cell development being delayed relative to that of αβT cells.…”

“…However, transcription of the genes encoding the B cell receptor associated molecules CD79a and CD79b was found in late stage embryos (Wang et al 2012b). To investigate this further, whole sections of 14 days postcoital embryos and 1 day postnatal neonates were also stained for CD79b, however the results were negative in all cases (not shown).…”

“…Previous analyses of B and T cell receptor transcription in the gray short-tailed opossum, Monodelphis domestica , clarified many aspects of the postnatal progression of lymphocyte development (Parra et al 2009; Wang et al 2012b). Recombination and transcription of the immunoglobulin heavy chain ( IgH ) locus was evident within 24 hours following birth but not in prenatal embryos (Wang et al 2012b).…”

“…Recombination and transcription of the immunoglobulin heavy chain ( IgH ) locus was evident within 24 hours following birth but not in prenatal embryos (Wang et al 2012b). Transcripts for the B cell markers CD79a and CD79b were detected in embryos at terminal pregnancy, consistent with B cell lineage commitment prenatally in opossums.…”