Lipopolysaccharide (LPS) was used to assess the responses of normal and tumor-bearing host (TBH) macrophages (M phi) to activation signals. M phi were incubated with LPS for either 3 hr or 24 hr and then assayed for phenotypic, functional, or cell-cycle changes. A 3-hr LPS treatment had no significant effect on M phi phenotype. In contrast, the 24-hr LPS treatment caused a significant decrease in the percentage of normal host Mac+ and Ia+ M phi. In the TBH, a 24-hr LPS treatment caused an increase in the percentage of Mac-1+ and -2+ M phi and a decrease in the percentage of Mac-3+ and Ia+ M phi. When normal host M phi were plated for 24 hr (control), there was an increase in Mac-1+ and -2+ M phi and a decrease in Ia+ M phi. The 24-hr TBH control showed a decrease in Mac-1+ and Ia+ M phi. To assess functional changes, LPS-treated normal and TBH M phi were added to the allogeneic mixed lymphocyte reaction (MLR) or the autologous MLR (AMLR). There were no significant differences in M phi accessory activity after a 3-hr LPS treatment. A 24-hr LPS treatment of normal host M phi also had no effect. A 24-hr LPS treatment of TBH M phi led to a significant decrease in allogeneic T-cell reactivity, and even the 24-hr TBH control showed significant suppression of T-cell responsiveness. In the AMLR, a measure of autoreactive T-cell responsiveness, a 3-hr LPS treatment had no affect on normal host M phi but led to increased accessory ability in TBH M phi. TBH M phi, however, were still less than 50% as responsive as normal host M phi even after LPS treatment. The 24-hr LPS treatment caused a significant decrease in normal or TBH M phi accessory activity. A 24-hr plating of normal host M phi decreased their accessory ability. In addition to the phenotypic and functional changes after LPS treatment, M phi cell-cycle kinetics were also investigated. The percentages of normal host M phi in G0/G1 were not changed significantly after a 3-hr LPS treatment. In contrast, M phi plated for 24 hr with or without LPS had a decreased percentage of cells in G0/G1. Normal host M phi showed little change in total RNA levels after a 3-hr treatment but had increased RNA levels after a 24-hr treatment.(ABSTRACT TRUNCATED AT 400 WORDS)