EFFECTS OF TRYPANOSOMA-EVANSI ON THE OUTPUT OF CELLS FROM A LYMPH-NODE DRAINING THE SITE OF PASTEURELLA-HAEMOLYTICA VACCINE ADMINISTRATION

The prefemoral efferent lymphatics of sheep infected with Typanosoma e vansi and inoculated with P. haemolytica vaccine and of those given on ly the vaccine, were surgically cannulated to study the effects of the infection on the total cellular output and output of blast cells from the node in response to the vaccine. T. evansi delayed and depressed the increases in total cell and lymphoblast outputs. In uninfected she ep, the total cellular output increased and peaked at more than twice the prevaccination values on days 4 and 5 after primary vaccination, b ut the increases were smaller and peaked on days 6 and 8 after primary vaccination in the infected sheep. The output of lymphoblasts mirrore d the total cell output, though it was suppressed to a greater degree by T. evansi. The output of blasts peaked at more than 8 and 14 times the prevaccination values in the uninfected animals after primary and secondary (booster) vaccinations, respectively; but in infected animal s, it peaked at twice the prevaccination values after the primary vacc ination and showed no increase after booster vaccination until 11 days later. It is concluded that the inhibition of total and blast cell ou tputs by T. evansi may limit the early systemic dissemination of antig en-specific cells, thus playing a role in the induction of immunosuppr ession by the parasite. (C) 1997 W.B. Saunders Company Limited.