Bone marrow-derived dendritic cells (DC) function as antigen presenting cells (APC). Little is known of their capability to exert regulatory effects on the epithelial cells in various organs. It was reported that injection of the bacterial cell wall preparation OK432 into mouse skin resulted in the activation of IL-1 and TNF-alpha gene expression in Langerhans cells (LC). In addition to studies on LC/DC in normal tissues, numerous investigators reported that DC can infiltrate primary tumors in experimental animals and humans and cause tumor regression. Human tumors in which DC infiltrates were detected did not develop metastases. The presence of DC in tumor biopsies correlated with the survival of patients. Absence of DC from tumors suggested poor prognosis. Activation of DC by immunomodulators seemed to enhance the ability of DC to prevent the development of metastatic tumors. Information on the role of DC as anticancer cells was recently reviewed, but information on the molecular basis of the anticancer activity of DC is needed. Another problem which needs to be answered is the ability of some tumors to prevent DC from entering the tumor. It is possible that DC and tumor cells, interact and counteract by releasing cytokines which abrogate tumor cells or DC, respectively. In the present analysis the DC responses to extrinsic cytokines and immunomodulators will be discussed. The ability of DC to induce the expression of the nitric oxide synthase gene will be discussed in relation to the anticancer activity of DC and in comparison with the reported anticancer activity of macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)