Initiation of the phosphocholine-specific response to Proteus morganii. B cell transfectants expressing unmutated VH/VL can respond to stimulation by P. morganii antigen.
We wished to resolve a paradox of how the response to the phosphocholine (PC) determinant of Proteus morganii could be initiated from a precursor B cell whose receptor, in unmutated form as Ab, appears to be unable to bind Ag. Unmutated VH and unmutated VL constructs were co-transfected into the B cell lymphoma M12.4 to study stimulation via membrane lg (mlg). The same VH construct was expressed in an L+, H- hybridoma line to characterize Ab binding. The unmutated Ab showed no detectable binding in ELISA to the PC-containing Ag from P. morganii PC(PM). By contrast, the unmutated mlg mediated mobilization of calcium in response to the PC(PM) Ag. Single-positive B cell lines of mlgM, mlgD double-positive lines were all capable of responding. The degree of signaling depended greatly on high receptor number, and only a fraction of cells in the population responded. Inhibition of the PC(PM)-induced calcium response by free PC indicated that the response was Ag-specific. A transfectant B cell line expressing moderate levels of a high affinity, mutated mlgM readily responded to PC(PM). These observations indicate that the unmutated lg as a receptor is capable of interacting with PC(PM) and suggest that the immune response to PC(PM) could originate from the precursor B cell expressing the unmutated mlg. The role of mlgD vs mlgM is discussed in terms of the requirement for high receptor number in the signaling process.
Penner
S J
SJ
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109, USA.
George
J
J
Claflin
L
L
D000595:Amino Acid Sequence; D000818:Animals; D000917:Antibody Formation; D000942:Antigens, Bacterial / Q000276:immunology*; D001402:B-Lymphocytes / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D000939:Epitopes / Q000276:immunology; D007072:Immunoglobulin D / Q000096:biosynthesis; D007143:Immunoglobulin Heavy Chains / Q000096:biosynthesis; D007147:Immunoglobulin Light Chains / Q000096:biosynthesis; D007075:Immunoglobulin M / Q000096:biosynthesis; D007135:Immunoglobulin Variable Region / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010767:Phosphorylcholine / Q000276:immunology*; D011511:Proteus / Q000276:immunology*; D014162:Transfection / Q000502:physiology; D014407:Tumor Cells, Cultured
D000942:Antigens, Bacterial; D000939:Epitopes; D007072:Immunoglobulin D; D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D007075:Immunoglobulin M; D007135:Immunoglobulin Variable Region; D010767:Phosphorylcholine; D002118:Calcium