Differential regulation of surface immunoglobulin expression by various muramyl dipeptides in a murine pre-B cell line

The murine pre-B cell line 70Z/3 responds to lipopolysaccharide (LPS), interleukin-1 (IL-1) or interferon-γ (IFNγ) by κ gene transcription and expression of surface IgM (sIg). We found that muramyl dipeptide (MDP), a synthetic immunoadjuvant analog of a bacterial membrane structure, produced a weak increase in the number of sIg-positive 70Z/3 cells as measured by immunofluorescence staining. This number was significantly increased after exposure to MDP. Moreover, when MDP was used in combination with LPS, IL-1 or IFNγ, an enhancement of sIg expression was observed showing an early influence of MDP in the presence of a second stimulant. Unexpectedly, two adjuvant-active analogs of MDP did not share its capacity to stimulate differentiation of the cell line when used alone or associated with other agents, indicating that adjuvanticity of MDP was not the only requirement. Two other products of bacterial origin, a Staphylococcus aureus cell extract (SAC) and the Toxic Shock Syndrome Toxin TSST-1 could neither enhance the κ gene expression in 70Z/3 cells nor increase the MDP effect. The stimulating effect displayed by MDP could be related to NF-κB activation.