CsA treatment reduces T-cell numbers, but does not alter CD4/CD8 ratio. (A) CsA treatment reduces T-cell numbers, but does not alter CD4/CD8 ratio. Rabbits were immunophenotyped after 2 weeks of CsA treatment. Rabbit lymphocytes were isolated from PBMC and examined for the following T-cell markers: T cell, CD4, and CD8. Twenty mg/kg CsA-treated rabbits had a statistically significant (P < .01) decrease in the number of T cells after 2 weeks of CsA treatment. (B) The CD4/CD8 ratio was not skewed during CsA treatment in either the 10 or 20 mg/kg CsA treatment groups. (C) CsA treatment suppresses T-helper cell responses to protein antigens and xenogeneic cells in rabbits. A lymphocyte proliferation assay was used to examine whether rabbit lymphocytes were functionally immune suppressed after CsA treatment. Before CsA treatment, rabbits were immunized with tetanus toxoid and Jurkat T cells. Two weeks after CsA treatment, rabbits treated with 20 mg/kg displayed statistically significant (P = .006) decrease in stimulation index to tetanus toxoid. The CsA-treated rabbits displayed decreases in stimulation index in tetanus toxoid and Jurkat T cells compared with control rabbits.