Bacterial lipopolysaccharide acts synergistically with selected macromolecular polyanions to induce MHC-nonrestricted...

We examined whether bacterial lipopolysaccharide, at a dose range extending to less than 1.0 ng/ml, would work with cofactors to induce MHC-nonrestricted cytotoxic cells. To this end, normal mouse splenocytes were cultured for 5 days with LPS and potential cofactors, after which the cells were tested for cytotoxic activity in short-term 51Cr-release assays. We found that LPS can act synergistically with the macromolecular polyanions, dextran sulfate and polyinosinic acid. The effector cells induced by LPS and polyanions showed characteristics of activated NK cells in that they were (1) cytotoxic for widely differing sources of tumor cells, (2) not inhibited by an anti-T cell receptor antibody, and (3) not removed by depletion of CD4+ or CD8+ cells. LPS was active at picogram concentrations when dextran sulfate was included. Exposure of splenocytes to LPS was necessary during the early phase of the 5-day culture, but as little as 1 h of exposure was required, whereas exposure to the macromolecular polyanions during either the first or the last 2 days of a 5-day culture with LPS was effective. As expected with LPS activity, the cytotoxic cell response was prevented by polymyxin B or by the use of splenocytes from LPS non-responder C3H/HeJ mice. Screening of the S. minnesota R mutants and other partial LPS structures revealed that lipid A was closely associated with LPS activity in this assay system and that at least one partially detoxified structure, a deacylated LPS, could substitute for native LPS.