In vivo and in vitro modulation of NK and ADCC activities of mouse spleen cells by peptidoglycan monomer (PGM).

The ability of peptidoglycan monomer (PGM), an immunomodulator obtained from Brevibacterium divaricatum, to modulate NK and ADCC activities of spleen cells was tested in mice with constitutively weak (C57B1) or strong NK activity (CBA, C3H). In weak reactors, i.v. injection of PGM enhanced the NK and ADCC activity as effectively as a known stimulator, poly I.C, and the dynamics of the response was comparable. In strong reactors, PGM caused two peaks of the ADCC response, and one peak of NK stimulation (after an initial decline), whereas poly I.C caused more or less persistent stimulation of both activities. Incubation of spleen cells with PGM was generally less effective than the treatment in vivo. No alteration of NK activity was recorded at high effector-to-target ratio (E:T), and at low ones, PGM caused suppression. This was true both for weakly and strongly reactive cells. ADCC was either unchanged (CBA spleen cells), stimulated (C3H), or suppressed at high E:T and enhanced at low E:T (C57B1). PGM apparently activates an interlocked regulatory mechanism, and the final outcome probably depends on relative concentrations of regulatory and effector cells and on their per cell activities. Hence the effect varied with the time interval between treatment and assay, with strain-related constitutive reactivity, and with the E:T ratio.