Trypanosome-induced suppression of responses to Trichinella spiralis in vaccinated mice

Mice vaccinated against the gastro-intestinal (GI) nematode Trichinella spi ralis by injection of muscle larval homogenate antigen express a strong imm unity to subsequent infection, reflected in earlier expulsion of adult worm s from the intestine and reduced female worm fecundity. Infection with Tryp anosoma brucei at the time of vaccination, or at the time of infection with T. spiralis, significantly reduced the level of immunity expressed, the ef fect being greatest when vaccination and T. brucei infection were given tog ether. Trypanosome infection reduced T. spiralis-specific antibody response s in vaccinated mice, the effect being most apparent against IgM, IgG1 and IgG2b, and ablated the eosinophil response to T. spiralis. In vaccinated mi ce infected with both trypanosomes and T. spiralis, the proliferative respo nses of lymphocytes to the mitogen Con A or to T. spiralis antigen were muc h lower than in vaccinated mice infected only with the nematode. Whereas ce lls from mice infected only with T. spiralis produced the cytokine IL-4 and little or no IFN gamma when stimulated in vitro, cells from animals infect ed with T. spiralis and with trypanosomes released large amounts of IFN gam ma, but no IL-4. These observations are consistent with the known, IFN gamm a-dependent, nitric-oxide-mediated suppressive effects of trypanosomes on l ymphocyte function and the Th1 bias associated with these infections, both of which reduce the effectiveness of the Th2-mediated responses involved in immunity against GI nematode infections. The data are discussed in the con text of the possible use of vaccines against GI nematodes in ruminants in c ountries where concurrent trypanosome-GI nematode infections are widespread . (C) 1999 Australian Society for Parasitology Inc. Published by Elsevier S cience Ltd. All rights reserved.