Evidence for host-mediated antitumor effects of lysozyme in mice bearing the MCa mammary carcinoma.

The host-mediated effects of lysozyme on primary tumor growth and on the formation of pulmonary metastases were investigated in mice bearing the MCa mammary carcinoma. The oral administration of lysozyme to CBA mice for 7 consecutive days before i.v. inoculation of MCa mammary carcinoma cells causes a significant reduction in the formation of lung tumors. The growth of s.c. tumors and the development of lung metastases is also significantly lowered in mice inoculated with tumor cells previously kept at 37 degrees C for 30 min in the presence of peritoneal resident cells or whole plasma samples obtained from normal mice treated with 25-100 mg/kg/day lysozyme for 7 consecutive days. The lysozyme concentration in plasma samples of the treated mice remains undetectable even at daily dosages up to 400 mg/kg, ruling out the hypothesis of a direct effect of the ingested lysozyme. These data seem to suggest a role for host immune reactivity in the antineoplastic effects of lysozyme. The results are consistent with previously reported data and further stress the interesting antitumor properties of the oral administration of lysozyme in mice bearing solid metastasizing tumors.