Factors Affecting the In Vitro Activation of Resident Peritoneal Macrophages by Mouse Interferon

Macrophage membrane glycoproteins that bind Griffonia simplicifolia I-B4: effect on cytotoxicity and protein secretion

Thioglycollate elicited peritoneal (TG-Møs) but not resident peritoneal Møs (R-Møs) were found to bind the lectin Griffonia simplicifolia isotype I-B4 (GSI-B4). This was demonstrated by ultrastructural studies and FACS analyses. Membranes from TG-Møs were isolated, separated on SDS-PAGE, electrotransferred onto nitrocellulose, and exposed to peroxidase-labeled GSI-B4. These procedures revealed two major membrane glycoproteins of molecular weights 180,000 and 94,000 daltons that bound the lectin GSI-B4 which has a specificity for recognizing terminal alpha-galactosyl residues. The presence of these epitopes on the two membrane glycoproteins was further substantiated by the fact that treatment of the membranes with alpha-galactosidase destroyed their capacity to bind GSI-B4 and that alpha-D-galactopyranoside but not N-acetyl-D-glucosamine competitively inhibited GSI-B4 from binding to the glycoproteins. Treatment of TG-Møs with GSI-B4 reduced the capacity of interferon (IFN) and lipopolysaccharide (LPS), or IFN alone, to induce Mø mediated cytotoxicity towards tumor cells by as much as 40%. GSI-B4 also caused alterations in the pattern of biosynthetically 35S-methionine labeled secreted proteins as early as 2 hours after contact with TG-Møs. Out of 35 discernible proteins on fluorograms of SDS-PAGE separated proteins, 5 were down-regulated and 9 were enhanced. It is suggested that the two novel Mø membrane proteins may play a role in regulating the response of Mø subpopulations to their humoral and cellular environments.

Induction of antitumor activity in macrophages by mycoplasmas in concert with interferon

The in vitro growth of tumor cells infected with mycoplasmas was suppressed by macrophages pretreated with interferon (IFN), but the growth of mycoplasma-free tumor cells was not suppressed. Pretreatment of macrophages with IFN plus mycoplasmas or their soluble factors either simultaneously or sequentially, IFN first and mycoplasmas second, but not in the reverse order, was effective in activating macrophages to suppress the growth of mycoplasma-free tumor cells. Macrophages from C3H/HeJ mice (which respond only slightly to lipopolysaccharide) were activated by IFN plus mycoplasmas or their soluble factor, and their action was not influenced by the addition of a lipopolysaccharide-neutralizing agent, polymyxin B. These results suggest that the macrophage-activating agent in mycoplasmas does not mimic lipopolysaccharide. The administration of mycoplasmas plus IFN to mice with ascitic or solid tumors resulted in the reduction of tumor growth. The survival rate of tumor-bearing mice was improved by the administration of mycoplasmas, and this was synergistically enhanced by the addition of IFN. These results indicate (a) that mycoplasmas can be useful as a biological response modifier, and (b) that care should be taken to prevent contamination with mycoplasmas in experiments on macrophage activation.