Cholera toxin acts synergistically with IL-4 to promote IgG1 switch differentiation.
Previously, we reported that cholera toxin (CT) causes LPS-stimulated membrane (m)IgM+ B cells to undergo increased switch differentiation to IgG- and IgA-producing B cells. In this study we determined whether this effect is specific for one or several of the IgG subclasses and whether B cells exposed to CT respond differently to IL-4, a lymphokine with switching capabilities. In initial studies we found that in LPS-stimulated, mIgM+ B cell cultures, CT eightfold enhanced the formation of IgG1-producing B cells, whereas it only weakly enhanced, one- to twofold, the formation of IgG3-producing B cells. In addition, CT synergistically enhanced the induction of IgG1-producing B cells by IL-4, even at plateau concentrations of IL-4. In contrast, IgM and IgG3 responses were suppressed in the CT plus IL-4-containing cultures as compared to those containing only LPS or LPS and CT. Furthermore, CT plus IL-4 had no enhancing effect on the formation of cells producing IgA; on the contrary, the presence of IL-4 led to a reversal of the stimulatory effect of CT on the IgA response. In further studies, we found that CT affected B cell differentiation at the gene level, before final gene recombination has occurred. Thus, CT together with LPS induced faint but detectable germline gamma 1 RNA transcripts not seen with cells cultured in LPS alone. However, more strikingly, CT enhanced by several-fold expression of germline gamma 1 RNA transcripts in LPS-stimulated B cell cultures containing optimal IgG1-inducing concentrations of IL-4. In addition, despite its weakly positive effect on IgG3 production. CT inhibited expression of germline gamma 3 RNA transcripts in cultures containing LPS and caused a further decrease in such transcripts in cultures containing LPS and IL-4. Finally, we found that CT enhanced the in vivo IgG1 but not the IgG3 or IgM anti-DNP serum antibody response of mice immunized with DNP-LPS. Taken together, these studies suggest that CT more strongly promotes B cell differentiation to IgG1 than to any other IgG subclass in LPS-stimulated cultures. CT acts alone or in synergy with IL-4, early in B cell differentiation to promote IgG1 expression in LPS-stimulated B cell cultures, probably by inducing early steps in the switch to this isotype such as the production of germline gamma 1 RNA transcripts.
Lycke
N
N
Department of Medical Microbiology and Immunology, University of Göteborg, Sweden.
Severinson
E
E
Strober
W
W
D000818:Animals; D000917:Antibody Formation / Q000187:drug effects; D001402:B-Lymphocytes / Q000187:drug effects* / Q000276:immunology; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology*; D004357:Drug Synergism; D007070:Immunoglobulin A / Q000096:biosynthesis; D007074:Immunoglobulin G / Q000096:biosynthesis* / Q000145:classification / Q000235:genetics; D015847:Interleukin-4 / Q000494:pharmacology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D012313:RNA / Q000032:analysis
D007070:Immunoglobulin A; D007074:Immunoglobulin G; D008070:Lipopolysaccharides; D015847:Interleukin-4; D012313:RNA; D002772:Cholera Toxin