CD5-positive and CD5-negative human B cells converge to an indistinguishable population on signalling through B-cell receptors and CD40.
Whether CD5 on B cells marks a subset functionally distinct from the conventional CD5 negative (CD5neg) adult population or is more an indicator of activation, remains contentious. Here we have investigated whether CD5 positive (CD5pos) and CD5neg B cells can be distinguished in terms of their response to surrogate signals aimed to model, in vitro, T-cell dependent (TD) and T-independent (TI) encounters with antigen in vivo: the predominantly CD5pos B-cell population found in cord blood, CD5 B cells positively selected from tonsils and their CD5neg counterparts, were compared. Neonatal B cells displayed a near-identical phenotype to that of adult CD5pos B cells, being characterized by uniform immunoglobulin M (IgM), immunoglobulin D (IgD), CD23 and CD44 coexpression. When cultured with anti-IgM maintained at high density on CD32-tranfected mouse L cells to model TI responses or on CD40 ligand (CD40L)-bearing L cells (with or without captured anti-IgM) to model TD encounters, DNA synthesis was stimulated to a similar extent in all three populations. Focusing on CD5 and CD23, we found that - although the signals delivered promoted distinct profiles of expression - under each condition of activation, the phenotypes that emerged for adult CD5pos and CD5neg B cells were remarkably similar. Neonatal B cells displayed a greater diminution in CD5 expression than adult CD5pos B cells following CD40 signals but otherwise the two populations again behaved similarly. The inclusion of interleukin-4 (IL-4) to cultures where cells were costimulated via surface (s)IgM and CD40 resulted in a complete loss of CD5 expression and a corresponding hyperexpression of CD23, irrespective of the population studied. The near-identical response of CD5pos and CD5neg B cells to surrogate TD or TI signals in vitro and their convergence to indistinguishable phenotypes is wholly supportive of CD5 being a fluctuating marker of activation rather than it delineating functionally distinct subsets.
Gagro
A
A
The Medical Research Council Centre for Immune Regulation, University of Birmingham, The Medical School, Birmingham, UK.
McCloskey
N
N
Challa
A
A
Holder
M
M
Grafton
G
G
Pound
J D
JD
Gordon
J
J
D000328:Adult; D000818:Animals; D016175:B-Lymphocyte Subsets / Q000276:immunology*; D019013:CD40 Antigens / Q000276:immunology*; D018956:CD5 Antigens / Q000032:analysis*; D018929:Cell Culture Techniques; D002453:Cell Cycle / Q000276:immunology; D002455:Cell Division / Q000276:immunology; D004247:DNA / Q000096:biosynthesis; D005312:Fetal Blood / Q000276:immunology; D006801:Humans; D016130:Immunophenotyping; D007231:Infant, Newborn; D008213:Lymphocyte Activation / Q000276:immunology; D051379:Mice; D014066:Palatine Tonsil / Q000276:immunology; D011947:Receptors, Antigen, B-Cell / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology*
D019013:CD40 Antigens; D018956:CD5 Antigens; D011947:Receptors, Antigen, B-Cell; D004247:DNA