The chicken B‐cell receptor complex and its role in avian B‐cell development

Abstract

The bursa of Fabricius is critical to normal B-lymphocyte development in birds. During embryonic life, B-cell precursors migrate to the bursal rudiment and those which have undergone productive V(D)J recombination colonize lymphoid follicles and undergo immunoglobulin V gene diversification by gene conversion. The chicken surface IgM complex appears structurally and functionally equivalent to its mammalian counterpart, with homologs to CD79a and CD79b. Expression of a truncated Igmu chain is sufficient to drive the early stages of B-cell development in the embryo bursa. Bursal cells expressing the truncated mu receptor complex proliferate in bursal follicles, and those which contain V gene rearrangements undergo V gene diversification by gene conversion. The bursa is a gut-associated organ and antigen is focused to bursal lymphoid follicles after hatch. While expression of the truncated mu chain is sufficient to support B-cell development in the embryo, B cells expressing this receptor are rapidly eliminated after hatch. We suggest the possibility that B-cell development in the bursa after hatch is driven by encounter with antigen leading to redistribution of B cells within the lymphoid follicle, B-cell proliferation and V gene repertoire development by gene conversion.

Notch1 enhances B-cell receptor-induced apoptosis in mature activated B cells without affecting cell cycle progression and surface IgM expression

“…10,11 Avian B-cell development proceeds differently: B-lymphoid precursor cells with a completely assembled BCR migrate into the Bursa of Fabricius, a gutassociated lymphoid tissue, where they are exposed to gutderived exogenous antigens and change their antigen specificity by gene conversion. 47 B-lymphoid cells that either lose the expression of surface Ig complexes or create a selfreactive BCR as a result of the gene conversion process are eliminated via apoptotic cell death in the bursa. 48 It is believed that the surface Ig complex is responsible for basal signaling levels in the absence of exogenous receptor ligation.…”

“…48 It is believed that the surface Ig complex is responsible for basal signaling levels in the absence of exogenous receptor ligation. 47 Taking these differences in murine and avian B-lymphopoiesis into account, it is highly likely that Notch1 exerts different functions in different hematopoietic lineages.…”

Structure and Implied Functions of Truncated B-Cell Receptor mRNAs in Early Embryo and Adult Mesenchymal Stem Cells: Cδ Replaces Cμ in μ Heavy Chain-Deficient Mice

“…Second, overexpression of the mesenchymal chain in 293T cells caused a morphological change that was not observed following overexpression of the full-length form of this molecule. The functions of other truncated Ig HC proteins, which have been character- ized in B cells, were also shown to be different from the functions of full-length rearranged Ig HC [9,14,40,[45][46][47][48][49][50][51]. Although D is functional [11,52,53], its activity is aberrant because it blocks further B-cell development [10,12,13].…”

Avian immunosenescence

“…Post-hatch, antigens from digested foods may enter the bursa due to reverse peristalsis of the hindgut. These antigens may drive normal post-hatch B-cell development (Glick 2000;Sayegh et al 1999Sayegh et al , 2000. IgM, IgG, IgA and IgY antibodies have been described in birds, but identical roles to mammalian forms have not been confirmed.…”