Effects of Trypanosoma brucei gambiense infections in Microtus montanus on susceptibility to Ehrlich's tumors.

Trypanosoma brucei gambiense infections in the field vole Microtus montanus increased susceptibility to Ehrlich's tumor growth. Whereas uninfected voles were totally resistant to intraperitoneal Ehrlich's ascites tumor cell challenge, over 78% of the animals infected with the trypanosomes developed tumors after challenge. Likewise, when Ehrlich's ascites cells were injected subcutaneously to induce solid tumor formation, only 7% of uninfected controls developed tumors, whereas over 82% of trypanosome-infected animals exhibited malignancies after Ehrlich's cell challenge. Finally, when solid tumors grown in albino CD-1 mice were implanted subcutaneously into uninfected voles, the tumor mass rapidly diminished in size and could not be found when animals were examined 2 weeks postimplant. However, in trypanosome-infected voles, implanted tumors exhibited pronounced expansion, and viable, solid tumors were recovered from over 70% of the challenged voles at 2 weeks postimplant. The implications of trypanosome-induced immunosuppression, especially toward susceptibility to neoplastic growth, are discussed.