Selective induction of high levels of IgA synthesis in Peyer's patch B cells by protein kinase C-activating phorbol esters.
To understand mechanisms of signal transduction involved in the regulation of isotype differentiation of B lymphocytes, we investigated effects of activation of protein kinase C (PKC) by phorbol esters and elevation of intracellular free calcium (Ca2+) by the calcium ionophore ionomycin (Ion) on Ig secretion by mouse Peyer's patch (PP) and spleen B cells. Results show that Ion suppressed production of IgM, IgG, and IgA by LPS-stimulated B cells whereas PKC-activating phorbol esters also inhibited LPS-induced IgM and IgG secretion, but induced a substantial IgA synthesis, as well as alpha-chain mRNA transcription, in B cells whether stimulated or not by LPS. Phorbol esters enhanced IgA response by directly activating PKC, inasmuch as the other phorbol ester, 4 alpha-phorbol 12,13-didecanoate, which is inactive with respect to PKC, had no effect on B cell differentiation. The increase in IgA secretion occurred in whole PP B cells, but not in the membrane IgA- B cell subset, suggesting that PKC activation does not promote the switching rate of IgM+ cells to IgA+ cells. Results from double staining studies of mIgA using FITC-labeled anti-IgA antibodies and DNA content using the DNA-binding propidium iodide showed that enhanced IgA response was not caused by IgA B cell clonal expansion. PMA induced low level of IL-6 production by highly purified PP B cells. However, addition of anti-mouse IL-6 antibody did not prevent PMA-enhanced IgA secretion, suggesting that IL-6 was not responsible for IgA induction by PMA. Collectively, the present data demonstrate that PKC activation and Ca2+ mobilization, which synergistically trigger cell proliferation, have differential effects on B cell isotype differentiation. Elevation of intracellular Ca2+ suppresses Ig production, but activation of PKC selectively enhances IgA secretion by directly promoting terminal differentiation of IgA-committed PP B cells into IgA-secreting plasma cells.
Li
Y S
YS
INSERM U80, CNRS URA1177, UCBL, Hôpital E. Herriot, Lyon, France.
Dearden-Badet
M T
MT
Revillard
J P
JP
D000818:Animals; D000917:Antibody Formation / Q000187:drug effects; D001402:B-Lymphocytes / Q000166:cytology / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D003593:Cytoplasm / Q000378:metabolism; D004789:Enzyme Activation; D007070:Immunoglobulin A / Q000096:biosynthesis*; D007137:Immunoglobulin alpha-Chains / Q000235:genetics; D015850:Interleukin-6 / Q000502:physiology; D015759:Ionomycin / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D010581:Peyer's Patches / Q000276:immunology*; D010703:Phorbol Esters / Q000494:pharmacology; D011493:Protein Kinase C / Q000502:physiology*; D011947:Receptors, Antigen, B-Cell / Q000032:analysis; D014158:Transcription, Genetic
D007070:Immunoglobulin A; D007137:Immunoglobulin alpha-Chains; D015850:Interleukin-6; D008070:Lipopolysaccharides; D010703:Phorbol Esters; D011947:Receptors, Antigen, B-Cell; D015759:Ionomycin; D011493:Protein Kinase C; D002118:Calcium