Identification of two IgD+ B cell populations in channel catfish, Ictalurus punctatus.
Channel catfish Ictalurus punctatus express two Ig isotypes: IgM and IgD. Although catfish IgM has been extensively studied at the functional and structural levels, much less is known about IgD. In this study, IgM(+)/IgD(+) and IgM(-)/IgD(+) catfish B cell populations were identified through the use of anti-IgM and anti-IgD mAbs. Catfish IgM(+)/IgD(+) B cells are small and agranular. In contrast, IgM(-)/IgD(+) B cells are larger and exhibit a plasmablast morphology. The use of cell sorting, flow cytometry, and RT-PCR demonstrated that IgD(+) B cell expression varies among individuals. For example, some catfish have <5% IgM(-)/IgD(+) B cells in their PBLs, whereas in others the IgM(-)/IgD(+) B cell population can represent as much as 72%. Furthermore, IgD expressed by IgM(-)/IgD(+) B cells preferentially associates with IgL σ. Comparatively, IgM(+)/IgD(+) B cells can express any of the four catfish IgL isotypes. Also, transfection studies show that IgD functions as a typical BCR, because Igδ-chains associate with CD79a and CD79b molecules, and all membrane IgD transcripts from sorted IgM(-)/IgD(+) B cells contain viable VDJ rearrangements, with no bias in family member usage. Interestingly, all secreted IgD transcripts from IgM(+)/IgD(+) and IgM(-)/IgD(+) B cells were V-less and began with a leader spliced to Cδ1. Importantly, transfection of catfish clonal B cells demonstrated that this leader mediated IgD secretion. Together, these findings imply that catfish IgM(-)/IgD(+) B cells likely expand in response to certain pathogens and that the catfish IgD Fc-region, as has been suggested for human IgD, may function as a pattern recognition molecule.
Edholm
Eva-Stina
ES
Department of Microbiology, University of Mississippi Medical Center, Jackson, MS 39216, USA.
Bengtén
Eva
E
Stafford
James L
JL
Sahoo
Manoranjan
M
Taylor
Erin B
EB
Miller
Norman W
NW
Wilson
Melanie
M
D000818:Animals; D016175:B-Lymphocyte Subsets / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D015153:Blotting, Western; D051925:CD79 Antigens / Q000276:immunology; D002469:Cell Separation; D005434:Flow Cytometry; D015870:Gene Expression; D005803:Genes, Immunoglobulin; D007059:Ictaluridae / Q000276:immunology*; D007072:Immunoglobulin D / Q000235:genetics / Q000276:immunology*; D047468:Immunoprecipitation; D020133:Reverse Transcriptase Polymerase Chain Reaction
D051925:CD79 Antigens; D007072:Immunoglobulin D