Tumor cytostasis mediated by LPS- or PSK-activated human plastic-adherent peripheral blood mononuclear cells

We investigated the mechanism of cytostasis mediated by activated human plastic-adherent peripheral blood mononuclear cells (PBMC) in two cell lines, L.P3 cells (TNF alpha sensitive) and A375 cells (TNF alpha insensitive), using two biological response modifiers, lipopolysaccharide (LPS) and a protein-bound polysaccharide extracted from a fungus, PSK. In L.P3/LPS, L.P3/PSK, and A375/LPS cultures, the cytostatic effects were significantly reversed by anti-TNF alpha antibody, while in the A375/PSK culture they were not. In concordance with this, LPS was a good inducer of TNF alpha, but PSK was not. In A375/PSK culture, PSK-activated cells arrested A375 cells at the boundary between G1 and S, presumably through inhibition of polyamine synthesis. This growth inhibition may be mediated by an unknown soluble factor which is different from TNF alpha, IL-1, IL-6, and TGF beta.