A method for investigating the role of homotypic adhesion in lymphocyte activation.
B cells activated via CD40 in vitro form striking homotypic aggregates, especially in the presence of costimuli such as anti-IgM, whereas those stimulated by anti-IgM alone do not. Blocking aggregation with anti-LFA-1alpha also significantly inhibits CD40-stimulated B cell proliferation, suggesting that homotypic adhesion is important for B cell activation via this receptor. To investigate this we have developed a culture system where murine B cells are stimulated in semi-solid agarose, which prevents cell-cell interactions. B cells respond to various mitogenic stimuli, including anti-CD40, in an essentially normal fashion when cultured in agarose. Furthermore, anti-LFA-1 exerts similar inhibitory effects on B cell proliferation regardless of whether the cells are in liquid, or semi-solid medium. These results indicate that homotypic aggregation is not necessary for CD40-stimulated B cell proliferation and the inhibitory effects of anti-LFA-1 could, therefore, be due to the delivery of a negative signal via this integrin, rather than as a result of inhibition of B cell clustering. Furthermore, reaggregation experiments indicated that anti-IgM-stimulated B cells are attracted into anti-CD40-generated clusters, even though they do not form clusters themselves. Taken together these results indicate that clustering is a consequence of B cell activation via CD40, rather than a necessary prelude to B cell proliferation. We postulate that homotypic aggregation may involve an unknown B cell-derived chemokine.
Cliff
J M
JM
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, WC1E 7HT, London, UK.
Klaus
G G
GG
D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000276:immunology / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology; D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology*; D019013:CD40 Antigens / Q000276:immunology; D002448:Cell Adhesion / Q000276:immunology; D002449:Cell Aggregation / Q000187:drug effects / Q000276:immunology; D002450:Cell Communication / Q000187:drug effects / Q000276:immunology; D018929:Cell Culture Techniques / Q000379:methods; D018799:Intercellular Adhesion Molecule-1 / Q000276:immunology; D008213:Lymphocyte Activation / Q000276:immunology*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008934:Mitogens / Q000494:pharmacology; D015203:Reproducibility of Results; D012685:Sepharose
D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal; D019013:CD40 Antigens; D016169:Lymphocyte Function-Associated Antigen-1; D008934:Mitogens; C044203:anti-IgM; D018799:Intercellular Adhesion Molecule-1; D012685:Sepharose