ANTIBODIES TO MURINE CD40 PROTECT NORMAL AND MALIGNANT B-CELLS FROM INDUCED GROWTH ARREST

We have previously described the production of polyclonal anti-murine CD40 antibodies that specifically bind recombinant murine CD40 express ed on L cells and induce vigorous proliferation of normal murine B lym phocytes. The current study utilizes these antibodies to explore the d istribution and function of CD40 in murine B cell development. Murine CD40 is expressed at high levels by normal splenic B cells and all Ig- positive B cell lymphomas tested to date. It is not expressed by the 7 0Z/3 pre-B cell line, BaF3 pre-B cell line, or by numerous T cell and myeloid cell lines. 70Z/3 pre-B cells can be induced to express CD40 b y LPS stimulation of the cells. Stimulation of purified splenic B cell s with anti-CD40 antibodies causes upregulation of class II MHC antige ns, CD23, and ICAM-1 and results in extensive aggregation of the cells . Antibodies to murine CD40 are extremely effective at rescuing malign ant and normal B cells from induced growth arrest. Anti-CD40 antibodie s protect WEHI-231 and CH31 B lymphoma cells from growth arrest induce d by soluble anti-IgM antibodies, TGF beta, or a combination of both s timulants. Similarly, anti-IgM preactivated normal splenic B cells whi ch normally die rapidly from growth arrest after 1 or 2 days culture p roduce a vigorous proliferative response to subsequent stimulation wit h anti-CD40 antibodies plus IL-4. Interestingly, anti-CD40 antibodies provide little to no protection against B lymphoma growth arrest induc ed by immobilized anti-IgM antibodies. These data confirm and extend f unctional properties assigned previously to human CD40 and identify nu merous defined murine model systems to explore the molecular basis of CD40-mediated protection from induced B cell growth arrest. (C) 1994 A cademic Press, Inc.