2,4,6-Trinitrophenyl (TNP) hapten-labeled peritoneal macrophages (Mf) given intravenously (iv) to recipients are poor inducers of contact sensitivity (CS) reactions unless Mf donors are pretreated with low doses of cyclophosphamide (CY). In vivo CY is converted into active alkylating metabolites, phosphoramide mustard (PM) and acrolein (ACR). Our experiments aimed to test how in vitro treatment of non-immunogenic Mf with different concentrations (10(-5) to 10(-7) M) of CY metabolites will influence their immunogenicity and other biological functions. Instead of chemically unstable PM, we used structurally and functionally similar nitrogen mustard (NM). Our experiments show that treatment of Mf with ACR or NM stimulates the in vitro production of pro-inflammatory IL-6 and IL-12 and down-regulates anti-inflammatory IL-10 and TGF-beta cytokines. In vivo non-immunogenic TNP-Mf become capable of inducing CS reactions in two situations: first, after treatment with NM or ACR and second, when cell recipients are received iv before Mf transfer of monoclonal antibodies against IL-10 and/or TGF-beta (500 mug per animal). Treatment with NM, but not with ACR, was also an efficient stimulus for production by Mf of significantly increased levels of reactive oxygen intermediates (ROIs). In summary, our experiments show that CY metabolites can significantly increase the specific immune response as well as nonspecific innate reaction (ROIs production) and support the notion that CY and its metabolites can be a promising accessory tool when upregulation of the immune response is desired.