Trypanosoma congolenseInfections: Induced Nitric Oxide Inhibits Parasite Growth In Vivo

Abstract

Wild-type (WT) C57BL/6 mice infected intraperitoneally with5×106Trypanosoma congolensesurvive for more than 30 days. C57BL/6 mice deficient in inducible nitric oxide synthase (iNOS−/−) and infected with 103or5×106parasites do not control the parasitemia and survive for only14±7or6.8±0.1days, respectively. Bloodstream trypanosomes of iNOS−/−mice infected with5×106  T. congolensehad a significantly higher ratio of organisms in the S+G2+M phases of the cell cycle than trypanosomes in WT mice. We have reported that IgM anti-VSG-mediated phagocytosis ofT. congolenseby macrophages inhibits nitric oxide (NO) synthesis via CR3 (CD11b/CD18). Here, we show that during the first parasitemia, but not at later stages of infection,T. congolense-infected CD11b−/−mice produce more NO and have a significantly lower parasitemia than infected WT mice. We conclude that induced NO contributes to the control of parasitemia by inhibiting the growth of the trypanosomes.