| The purpose of this study was to test the hypothesis that CD4+ T lymphocytes are required in calves during acute anaplasmosis. In the first experiment, a long-term in vivo CD4+ T lymphocyte depletion model was developed and validated. Both thymectomy and treatment with anti-CD4 mAb were shown to be required for long-term in vivo depletion of functional CD4+ T lymphocytes. Thymectomized, anti-CD4 mAb-treated calves were depleted of functional CD4 + T lymphocytes for at least 8-weeks and had significant abrogation of lymphoproliferative responses to ovalbumin as well as decreased IgG1 and no detectable IgG2 antibody responses to ovalbumin, compared to thymus-intact anti-CD4 mAb-treated calves. In the second experiment, thymectomized calves were selectively depleted of CD4+ T lymphocytes followed by experimental infection with the Florida strain of A. marginale. Despite significant long-term depletion of CD4+ T lymphocytes, thymectomized anti-CD4 mAb-treated calves were able to control acute infection and developed both IgG1 and IgG2 anti-A. marginale antibody responses. Anti-CD4 mAb-treated calves had higher parasitemias and greater reductions in packed cell volume than non-depleted calves, however these differences were not significant. |
