CD40-mediated lymphotoxin alpha expression in human B cells is tyrosine kinase dependent.
The cytokine lymphotoxin (LT)alpha is known to play a role in B cell activation. As the engagement of the B cell antigen CD40 is known to lead to B cell proliferation and differentiation, we studied LT alpha expression in human B cells after CD40 ligation. We demonstrate that anti-CD40 monoclonal antibody (mAb) induces strong LT alpha mRNA and surface-expression in human tonsil B cells. Induction of LT alpha mRNA and surface expression by CD40 ligation is inhibited by the protein tyrosine kinase (PTK) inhibitors herbimycin and genistein in a dose-dependent manner. The protein kinase C (PKC)-specific inhibitors sphingosine and bis-indolylmaleimide caused negligible inhibition of anti-CD40-induced LT alpha mRNA and surface expression. No inhibition is observed with the protein kinase (PKA) inhibitors H89 and HA1004. Cross-linking of the transmembrane phosphatase CD45 to CD40 by using goat-anti-mouse F(ab')2 fragments strongly inhibits CD40-mediated LT alpha expression in human B cells, confirming the role of PTK activation in CD40-mediated induction of LT alpha expression. Inhibitors of the serine/threonine protein phosphatases PP1 and PP2A, okadaic acid and calyculin induce LT alpha mRNA expression. In contrast, cyclosporin A, an inhibitor of the serine/threonine phosphatase calcineurin has no effect on anti-CD40-induced LT alpha expression. These results suggest that induction of LT alpha expression in B cells following engagement of CD40 involves activation of protein tyrosine kinases.
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Children's Hospital/Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA.
Geha
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RS
D000911:Antibodies, Monoclonal; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D019013:CD40 Antigens / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D017493:Leukocyte Common Antigens / Q000276:immunology / Q000378:metabolism; D008233:Lymphotoxin-alpha / Q000096:biosynthesis*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D015398:Signal Transduction
D000911:Antibodies, Monoclonal; D019013:CD40 Antigens; D008233:Lymphotoxin-alpha; D012333:RNA, Messenger; D011505:Protein-Tyrosine Kinases; D017493:Leukocyte Common Antigens