title: Antigen receptor proximal signaling in splenic B-2 cell subsets.
abstract: Splenic marginal zone (MZ) and follicular mantle (FO) B cells differ in their responses to stimuli in vitro and in vivo. We have previously shown that MZ cells exhibit greater calcium responses after ligation of membrane IgM (mIgM). We have now investigated the molecular mechanism underlying the difference in calcium responses following ligation of mIgM and studied the response to total B cell receptor ligation in these two subsets. We compared key cellular proteins involved in calcium signaling in MZ and FO cells. Tyrosine phosphorylation and activity of phospholipase C-gamma 2 and Syk protein tyrosine kinase were significantly higher in MZ cells than in FO cells after mIgM engagement, providing a likely explanation for our previous findings. Tyrosine phosphorylation of CD22 and expression of Src homology 2-containing inositol phosphatase and Src homology 2-containing protein tyrosine phosphatase-1 were also higher in the MZ cells. Expression and tyrosine phosphorylation of Btk, BLNK, Vav, or phosphatidylinositol 3-kinase were equivalent. In contrast, stimulation with anti-kappa induced equivalent increases in calcium and activation of Syk in the two subsets. These signals were also equivalent in cells from IgM transgenic, J(H) knockout mice, which have equivalent levels of IgM in both subsets. With total spleen B cells, Btk was maximally phosphorylated at a lower concentration of anti-kappa than Syk. Thus, calcium signaling in the subsets of mature B cells reflects the amount of Ig ligated more than the isotype or the subset and this correlates with the relative tyrosine phosphorylation of Syk.
authors.affiliation: Department of Medicine, University of Alabama, Birmingham, AL 35294, USA.
authors.forename: X
authors.initials: X
authors.lastname: Li
authors.forename: F
authors.initials: F
authors.lastname: Martin
authors.forename: A M
authors.initials: AM
authors.lastname: Oliver
authors.forename: J F
authors.initials: JF
authors.lastname: Kearney
authors.forename: R H
authors.initials: RH
authors.lastname: Carter
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology; D016175:B-Lymphocyte Subsets / Q000166:cytology / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism*; D002454:Cell Differentiation / Q000276:immunology; D004306:Dose-Response Relationship, Immunologic; D004789:Enzyme Activation / Q000235:genetics / Q000276:immunology; D004792:Enzyme Precursors / Q000378:metabolism; D007075:Immunoglobulin M / Q000235:genetics / Q000276:immunology / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000235:genetics / Q000494:pharmacology / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D013154:Spleen / Q000033:anatomy & histology / Q000166:cytology* / Q000201:enzymology / Q000276:immunology*; D000072377:Syk Kinase; D010738:Type C Phospholipases / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism / Q000502:physiology
chemical_list: D000888:Antibodies, Anti-Idiotypic; D004792:Enzyme Precursors; D007075:Immunoglobulin M; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D011947:Receptors, Antigen, B-Cell; C044203:anti-IgM; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D010738:Type C Phospholipases; D051966:Phospholipase C gamma