The Journal of Immunology, Vol 151, Issue 11 5936-5947, Copyright © 1993 by American Association of Immunologists

ARTICLES

Administration of anti-CD45 mAb specific for a B cell-restricted epitope abrogates the B cell response to a T-dependent antigen in vivo

R Domiati-Saad, EW Ogle and LB Justement
Department of Microbiology, University of Texas Medical Branch, Galveston 77555-1019.

CD45 is a receptor-like protein tyrosine phosphatase expressed exclusively by cells of the hemopoietic lineage. Studies in vitro involving treatment of B cells with anti-CD45 mAb have demonstrated that ligand binding to CD45 alters the cell's response to various activation/differentiation stimuli. In general anti-CD45 treatment has been shown to exert an inhibitory effect on early activation events resulting in the failure of quiescent B cells to enter the cell cycle. These studies suggest that CD45 acts as an important regulatory molecule in vitro, that controls B cell function. In contrast, little is known concerning the role that CD45 plays in vivo regarding regulation of B cell activation and differentiation in response to T- dependent Ag. In our study the anti-CD45 mAb RA3.6B2, which recognizes a B cell-restricted epitope, was used to examine this question. Administration of anti-CD45 mAb in vivo was found to inhibit the proliferative response of splenocytes when stimulated with B cell-, but not T cell-specific mitogens. Immunization with the T-dependent Ag FITC- KLH in the presence of increasing amounts of anti-CD45 mAb resulted in a significant, dose-dependent inhibition of the plaque-forming cell response. Additionally, anti-CD45 mAb inhibited the production of FITC- specific serum antibodies indicating that the effect was systemic. Finally, anti-CD45 mAb appeared to exert a maximal effect at earlier time points, within 48 h of Ag administration, suggesting that B cell activation was primarily affected. These results provide evidence to support the conclusion that CD45 is an important regulatory molecule that is involved in the control of B cell activation in vivo.

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