Reactivity of anti-asialo GM1 serum with tumoricidal and non-tumoricidal mouse macrophages

All peritoneal macrophage (pMΦ) populations studied exhibited some binding of the anti-asGM1 serum as assessed by flow cytometry. The levels of reactivity varied quantitatively among populations, depending on the combination of eliciting and activating agents employed prior to the harvest of pMΦ. Resident pMΦ contained a very small percentage (4%) of cells that were strongly asGM1 +. Any treatment of these cells that induced them to become stimulated or activated increased the percentage of highly asGM1 + cells. Treatments that enhanced anti-asGM1 binding including eliciting pMΦ with proteose peptone (16% asGM1 +) or Brewer's thioglycollate medium (66% asGM1 +), treatment with the activating biological response modifiers (BRMs) MVE-2 (12% asGM1 +) and P acnes (18% asGM1 +), or treatment with both peptone + MVE-2 (37% asGM1 +) or peptone + poly IC/LC (33%). Increased expression of anti-asGM1 was accompanied by some increase in the reactivity of the various pMΦ populations to treatment with anti-asGM1 serum. This conclusion was based on the reduced viabilities of cells treated with both an eliciting agent and an activating agent prior to in vitro treatment with anti-asGM1 + C, as well as by reductions in cytolytic activity of pMΦ elicited with peptone and activated by MVE-2, following anti-asGM1 treatment in vitro or administration in vivo. Conversely, the cytolytic activity of resident pMΦ activated in vivo by MVE-2 or heat-killed P acnes, agents that induced relatively small increases in the percentage of asGM1 + cells, was resistant to the effects of in vivo and/or in vitro treatment with doses of anti-asGM1 serum that inhibit NK activity. These results indicate that stimulation of pMΦ by eliciting or activating agents can increase the level of expression of asGM1. This increased expression of asGM1 may be a useful marker for some aspects of macrophage heterogeneity, but increased expression is not necessarily directly related to expression of tumoricidal activity. In fact, the results of this study demonstrate that anti-asGM1 serum can be used for specific depletion of NK activity in vivo in normal mice and in mice treated with at least some BRMs. However, the results also demonstrate that the use of eliciting agents, particularly thioglycollate, or eliciting agents in conjunction with activating agents can cause pMΦ to become reactive with anti-asGM1 serum.