Induction of CD4(+)CD8(+) double positive T cells and increase in CD5(+) Bcells in efferent lymph in sheep infected with Trypanosoma evansi

The effects of Trypanosoma evansi on efferent lymphocyte phenotypes drainin g from a lymph node primed with Pasteurella haemolytica vaccine were studie d in sheep. The prefemoral efferent lymphatic ducts of the infected sheep a long with those of two uninfected sheep were surgically cannulated. Lymph w as collected and lymphocytes recovered from it analysed by two-colour indir ect immunofluorescence staining and cytofluoremetry in a fluorescence activ ated cen analyser (FACSCAN). The study showed the appearance and persistenc e of T. evansi in the efferent lymph for a long period of time and the appe arance of CD4(+)CD8(+) (double positive, DP) T lymphocytes in the efferent lymph of infected animals. The infection also resulted in increases in CD5( +) B cells in the prefemoral efferent lymph. In addition, there were decrea ses in the output of conventional B cells, CD5(+) and CD4(+) T cell subsets but large increases in CD8(+) cells followed by terminal depletion of all cell subsets. In contrast, inoculation of sheep with pasteurella vaccine an tigen alone produced little alterations in the proportions, but large incre ases in the numbers of all T cell subsets except that of CD8(+) cells which also showed little variation; and there was a concurrent increase in the n umbers and proportions of efferent B cells. In addition, the abnormal expre ssion of DP and CD5(+) B cells did not occur in the uninfected vaccinated s heep. It is concluded that these abnormal changes in the kinetics of effere nt lymphocyte phenotypes are likely to play a role in the genesis of the ge neralized immunosuppression seen in trypanosome-infected hosts.