To investigate the effects of maedi-visna virus (MVV) infection on cell-mediated immunity, the in vitro response of bronchoalveolar lavage fluid (BALF) and peripheral blood (PB) lymphocytes (PBL) to exogenous mitogen was analysed. BALF and PBL from control (n = 9) and MVV-infected (n = 7) animals were cultured for 3 days in the presence and absence of concanavalin A (Con A). Lymphocyte expression of the interleukin-2 receptor (IL-2R) antigen, a parameter of lymphocyte activation, was quantified by dual-colour flow cytometry using the bovine anti-IL-2R monoclonal antibody IL-A111. 1L-2R expression by lymphocytes in BALF and PB from control and MVV-infected animals, with and without Con A stimulation, were compared. In the absence of Con A stimulation, the proportion of cultured BALF CD8(+) and gamma delta T cells expressing IL-2R was significantly (P < 0.05) lower for MVV-infected animals than for controls. After Con A stimulation the proportion of BALF CD4(+) lymphocytes from MVV-infected animals that expressed IL-2R remained significantly (P < 0.05) lower than for controls. Comparisons within group showed that, after Con A stimulation, the proportion of all the T cell subsets in the control group expressing IL-2R, namely CD4(+) (P < 0.001), CD8(+) (P < 0.001) and gamma delta T cells (P < 0.05), was significantly increased. In the MW-infected group, this increase was significant (P < 0.05) for CD4(+) and CD8(+) T cells, but not for gamma delta T cells. In vitro mitogen stimulation of PB T lymphocytes from both control and MVV-infected animals induced a significant elevation in the proportion of all T cell subsets expressing IL-2R when compared to cultured unstimulated control cells. However, there was considerable heterogeneity in the response to Con A of PB T cells from both groups of animals. The expression of IL-2R followed a different pattern to that of BALF lymphocytes, the proportion of unstimulated gamma delta/IL-2R(+) T cells from MW-infected animals being significantly (P < 0.05) higher than that of controls, and the proportion of cultured unstimulated CD8(+)/IL-2R(+) T cells from MVV-infected animals being significantly (P < 0.05) lower than that from controls. From these studies it can be concluded that the BALF T lymphocyte immune dysfunction observed during natural MVV infection, characterized by impaired IL-2R expression, is maintained under in vitro conditions.
