Different patterns of inositol polyphosphate production are seen in B lymphocytes after cross-linking of sIg by anti-Ig antibody or by a multivalent anti-Ig antibody dextran conjugate.
Anti-delta antibody conjugated to 2 x 10(6) m.w. dextran (dex) stimulates B lymphocyte proliferation at 10,000-fold lower concentrations than that required by the unconjugated antibody. Dex conjugated antibody also stimulates a greater and more sustained increase in intracellular ionized calcium [( Ca2+]i) than does the unconjugated anti-Ig antibody. Inasmuch as inositol phosphate metabolites have been linked to rises in [Ca2+]i, we analyzed by FPLC the relative amounts of the inositol polyphosphates (IP) in these cells. Anti-Ig-dextran induced a threefold greater increase in total IP than did the unconjugated anti-Ig. Furthermore, in cells stimulated by unconjugated anti-Ig there was a transient induction of I(1,4,5)P3 followed by a rapid accumulation of the I(1,3,4)P3 isomer with little accumulation of I(1,4)P2, whereas in anti-Ig-dex-stimulated cells there was prolonged elevation of I(1,4,5)P3 with more accumulation of I(1,4)P2. In addition, levels of I(1,3,4,5)P4 were maintained over a longer period of time in B cells stimulated by anti-Ig-dex than in those stimulated by unconjugated anti-Ig. The enhanced ratio of I(1,4,5)P3/I(1,3,4)P3 was also seen when suboptimal concentrations of anti-Ig-dex were used which stimulated a level of total inositol phosphate that was similar to that stimulated by the unconjugated anti-Ig. The possibility that the greater stimulation of increased [Ca2+] by anti-Ig-dex than by unconjugated anti-Ig was a predominant factor in influencing the metabolic pathway of I(1,4,5)P3 was excluded. These results show that 1) stimulation of increases in the various IP isomers occurs in anti-Ig stimulated normal B cells as has been shown in B cell lines and 2) that signal transduction and consequent PIP2 hydrolysis that is stimulated by Ag-mediated cross-linking of sIg is strongly influenced by the extent and type of cross-linking that is induced.
Brunswick
M
M
Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD 20814-4799.
June
C H
CH
Finkelman
F D
FD
Mond
J J
JJ
D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology*; D001402:B-Lymphocytes / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism; D003911:Dextrans / Q000494:pharmacology*; D004306:Dose-Response Relationship, Immunologic; D005260:Female; D006868:Hydrolysis; D007072:Immunoglobulin D / Q000276:immunology* / Q000494:pharmacology; D007295:Inositol Phosphates / Q000096:biosynthesis*; D051379:Mice; D008811:Mice, Inbred DBA; D008819:Mice, Nude; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism* / Q000494:pharmacology; D013403:Sugar Phosphates / Q000096:biosynthesis*
D000888:Antibodies, Anti-Idiotypic; D003432:Cross-Linking Reagents; D003911:Dextrans; D007072:Immunoglobulin D; D007295:Inositol Phosphates; D019269:Phosphatidylinositol 4,5-Diphosphate; D010716:Phosphatidylinositols; D011947:Receptors, Antigen, B-Cell; D013403:Sugar Phosphates; C039951:anti-IgD; D002118:Calcium