Modulation of Expression of Class II MHC and CD40 Molecules in Murine B Cells by Various Muramyl Dipeptides

Several compounds of the MDP (muramyl dipeptide) series which have the capacity to enhance the immune response to antigens exerted a comitogenic effect on murine splenic B cells. The expression of surface class II major histocompatibility and CD40 antigens was used to more accurately evaluate the comparative influence of the synthetic agents on mature B cells and on the pre-B cell line 70Z/3. MDP and two adjuvant-active analogs enhanced expression of both surface molecules and increased the response to lipopolysaccharide (LPS) or interferon-γ (IFN-γ) in splenic B cells. The three synthetic adjuvants alone did not lead to expression of cell-surface I-Ador CD40 in 70Z/3 cells, indicating that they were unable by themselves to achieve differentiation of pre-B cells to a mature B cell phenotype. However, they increased the CD40 level induced by treatment with LPS. In this cell line, the response (CD40 protein and mRNA) to IFN-γ was strongly increased by MDP but not by the two other compounds. Actually, MDP was the only adjuvant among the three compounds to functionally activate the transcription factor NF-κB, to induce κ transcription, and to stimulate surface κ light-chain expression in 70Z/3 cells. The response to muramyl dipeptides in mature splenic B cells could appear independent of the transcription factor.