Restricted IgA Repertoire in Both B-1 and B-2 Cell-Derived Gut Plasmablasts

Abstract

Mucosal IgA is the most abundantly produced Ig upon colonization of the intestinal tract with commensal organisms in the majority of mammals. The repertoire of these IgA molecules is still largely unknown; a large amount of the mucosal IgA cannot be shown to react with the inducing microorganisms. Analysis of the repertoire of used H chain Ig (VH) genes by H-CDR3 spectrotyping, cloning, and sequencing of VH genes from murine intestinal IgA-producing plasma cells reveals a very restricted usage of VH genes and multiple clonally related sequences. The restricted usage of VH genes is a very consistent observation, and is observed for IgA plasma cells derived from B-1 or conventional B-2 cells from different mouse strains. Clonal patterns from all analyzed VH gene sequences show mainly independently acquired somatic mutations in contrast to the clonal evolution patterns often observed as a consequence of affinity maturation in germinal center reactions in peripheral lymphoid organs and Peyer’s patches. Our data suggest a model of clonal expansion in which many mucosal IgA-producing B cells develop in the absence of affinity maturation. The affinity of most produced IgA might not be the most critical factor for its possible function to control the commensal organisms, but simply the abundance of large amounts of IgA that can bind with relatively unselected affinity to redundant epitopes on such organisms.

Molecular characterization of the cervical and systemic B-cell repertoire

“…The presence of these shared mutations suggests strongly that affinity maturation occurred in the peripheral blood prior to class switching and diversification. 21,52,53 Furthermore, the number of mutations observed in each parent PBMC clone in Figure 5 suggests that the B cells migrating to the cervix have undergone one or more germinal center reactions resulting in somatic mutation and is consistent with our finding that for most isotypes, antigen selection is higher systemically than mucosally. Obviously, the location of IgM PBMC clone 44 as an intermediate between IgA CMC clones 33 and 19 in Figure 5 is in violation of the class switching rules.…”

Recognition of Gram-positive Intestinal Bacteria by Hybridoma- and Colostrum-derived Secretory Immunoglobulin A Is Mediated by Carbohydrates

“…The intestinal microbiota have been demonstrated to be involved in the proper development of the intestinal immune system and in particular in the production of a diverse repertoire of SIgA (4) composed of at least 90% of natural SIgA with largely unknown specificity (8,15,16). The biological function of such SIgA remains speculative; however, various studies have underscored the natural coating of commensal bacteria by SIgA, a process that may be involved in the homeostatic gut sensing of the microbiota (12,41,44).…”

T Cell-Independent IgA Class Switch Recombination Is Restricted to the GALT and Occurs Prior to Manifest Germinal Center Formation

“…To ensure analysis of follicle-free sections, 2-3-cm pieces of the colon were frozen and sectioned as described (30,36). Every fifth section was placed on a slide, and the sections in between were stored in buffer RLT (Qiagen) at 270˚C.…”