Tumor-suppressive effect of a cell wall preparation, WPG, from Bifidobacterium infantis in germfree and flora-bearing mice

A cell wall preparation (whole peptidoglycan, WPG) derived from Bifidobacterium infantis exhibited antitumor activity when WPG and Meth A cells were mixed and injected subcutaneously (suppression test) in flora-bearing (FB) BALB/c mice. This antitumor activity was markedly reduced when the germfree (GF) BALB/c mice were used as a host. Histological examination of the injected site revealed vigorous polymorphonuclear leukocyte (PMN) infiltration and tumor cell degeneration at day 1 to 3 postimplantation of WPGMeth A mixture in both FB and GF mice, but later on re-appearance of tumor cell mass was seen in many GF but in only a few FB mice. Similar but somewhat weaker suppressive effects of WPG were seen in FB athymic nu/nu mice in which severe PMN infiltration was also developed. Results indicated that the early inflammatory reaction composed mostly of PMN played a role as the major effector mechanisms in the suppression test, and inferior antitumor activity of PMN from GF mice to that from FB mice was implicated. However, since FB euthymic but not FB nu/nu mice showed development of antitumor immunity in re-implantation, involvement of immunological capacity might have played an additional role in the suppression efficiency.