Contribution of cytokines on the suppression of lung metastasis.

Weekly injection of a protein-bound polysaccharide PSK in mice with Lewis Lung Cancer (LLC) significantly decreased the number of lung metastatic foci concomitant with enhancement of cytostatic activity in the bronchoalveolar lavage (BAL) cells. These effects were more marked when the agent was given intratracheally, inducing a larger number of pulmonary macrophages, lymphocytes and neutrophils concomitant with increases in BAL tumor necrosis factor-alpha (TNF-alpha), mouse inflammatory protein-alpha (MIP-1alpha), mouse inflammatory protein-beta (MIP-1beta), interleukin-1alpha (IL-1alpha) and interleukin-6 (IL-6), but not interleukin-2 (IL-2) and interleukin-4 (IL-4). Pre-treatment with anti TNF-alpha antibody reduced these effects. The time course and production of PSK-induced cytokines were similar between the tumor-bearing mice and control mice. BAL neutrophils in mice with LLC showed a tendency toward acceleration of O2- production compared with circulating neutrophils. Pulmonary macrophage phagocytosis was also significantly higher in the LLC mice. These results suggest that enhancement of cytostasis appears to be induced by activation and/or improvement of function in inflammatory and immune cells through cytokines under immunomodulator treatment in lung metastasis, possibly via a TNF-alpha-dependent mechanism.