title: CD19 signaling is impaired in murine peritoneal and splenic B-1 B lymphocytes.
abstract: B-1 cells reside predominantly within the coelomic cavities, tonsils, Peyer's patches, spleen (a minor fraction - approximately 5%) and are absent in the lymph nodes. They are the primary sources of natural IgM in the body. B-1 cells express polyreactive B cell receptors (BCRs) that cross react with self-antigens and are thus implicated in auto-immune disorders. Previously, we reported that peritoneal B-1 cells are deficient in CD19-mediated intracellular signals leading to Ca(2+) mobilization. Here, we find that splenic B-1 cells, like peritoneal B-1 cells, are defective in Ca(2+) release upon B cell activation by co-cross-linking BCR and CD19. In the absence of extracellular sources of Ca(2+), intracellular Ca(2+) flux is similar between B-1 and B-2 cells. Moreover, the intracellular component of Ca(2+) release in both subsets of B cells is mostly PI3K dependent. BCR and CD19 co-cross-linking activates Akt, a key mediator of survival and proliferation signals downstream of PI3K in splenic B-2 cells. Splenic B-1 cells, on the other hand, do not phosphorylate Akt (S473) upon similar treatment. Furthermore, BCR+CD19 cross-linking induced phosphorylation of JNK is much reduced in splenic B-1 cells. In contrast, B-1 cells exhibited increased levels of constitutively active pLyn which appears to have an inhibitory role. The CD19 induced Ca(2+) response and BCR induced proliferation response were restored by a partial inhibition of pLyn with Src kinase specific inhibitors. These findings suggest a defect in CD19-mediated signals in both peritoneal and splenic B-1 B lymphocytes, which is in part, due to higher levels of constitutively active Lyn.
authors.affiliation: Department of Microbiology, Immunology & Molecular Genetics, University of Kentucky, Lexington, 40536-0298, United States.
authors.forename: Trivikram
authors.initials: T
authors.lastname: Dasu
authors.forename: Vishal
authors.initials: V
authors.lastname: Sindhava
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Clarke
authors.forename: Subbarao
authors.initials: S
authors.lastname: Bondada
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D018941:Antigens, CD19 / Q000276:immunology*; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D019013:CD40 Antigens / Q000276:immunology; D018956:CD5 Antigens / Q000276:immunology; D002118:Calcium / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D015151:Immunoblotting; D017493:Leukocyte Common Antigens / Q000276:immunology; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D016177:Macrophage-1 Antigen / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D010537:Peritoneum / Q000166:cytology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011720:Pyrazoles / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology*; D013154:Spleen / Q000166:cytology; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: C108123:4-amino-5-(4-methylphenyl)-7-(tert-butyl)pyrazolo(3,4-d)pyrimidine; D000906:Antibodies; D018941:Antigens, CD19; D019013:CD40 Antigens; D018956:CD5 Antigens; D004791:Enzyme Inhibitors; D016177:Macrophage-1 Antigen; D011720:Pyrazoles; D011743:Pyrimidines; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D051057:Proto-Oncogene Proteins c-akt; D048670:MAP Kinase Kinase 4; D017493:Leukocyte Common Antigens; D002118:Calcium