Antitumor Effect of PSK at a Distant Site: Inductions of Interleukin‐8‐like Factor and Macrophage Chemotactic Factor in Murine Tumor

The antitumor effect of PSK, a Coriolus preparation, at a distant site was analyzed with the use of a double grafted tumor system in which male BALB/c mice received simultaneous intradermal inoculations of Meth‐A tumor in the right (10(6) cells) and the left (2 × 10(5) cells) flanks and were then injected with PSK in the right tumor on the third day thereafter. The antitumor effect of intratumoral administration of PSK in the right tumor on days 3, 4 and 5 was compared with the effect of surgical resection of the right tumor on day 5. Three out of 8 mice given PSK intratumorally became tumor‐free whereas no mouse tumor‐free in the left flank was found among the surgically resected mice. As regards sinecomitant immunity, tumor inoculation into the right flank followed by intratumoral administration of PSK on days 3 and 5 and surgical excision of the primary tumor on day 6 resulted in complete rejection of a tumor challenge in the left flank on day 21. The combination of presurgical intratumoral injections of PSK (more than 2 times) and postoperative oral administration of PSK appeared to be most effective in eradicating secondary tumors. Isolated TILs (tumor‐infiltrating lymphocytes), obtained from the right tumor (treated with PSK) and the left tumor on day 10 in the double grafted tumor system were cultured in RPMI1640 with 10% fetal calf serum for 24 h. The culture supernatants were harvested and tested for the presence of chemotactic activity for neutrophils or macrophages. Significant neutrophil chemotactic factor (NCF) and macrophage chemotactic factor (MCF) activities were detected in the culture media from PSK‐treated TILs that had been cultured for 24 h. Neither significant neutrophil nor macrophage chemotactic activity was detected in the media from untreated TILs. NCF and MCF activities were also detected in the culture supernatant from PSK‐treated tumor tissue on day 6. PSK‐induced NCF in the murine tumor was neutralized by treatment with anti‐human IL‐8 IgG, and might be murine IL‐8‐like factor. Therefore, neutrophil and macrophage infiltrations of tumors following intratumoral injections of PSK are probably mediated by inductions of IL‐8‐like factor and MCF.