IN-VITRO RESPONSE OF LYMPHOCYTES FROM BRONCHOALVEOLAR LAVAGE FLUID AND PERIPHERAL-BLOOD TO MITOGEN STIMULATION DURING NATURAL MAEDI-VISNA VIRUS-INFECTION

To investigate the effects of maedi-visna virus (MVV) infection on cel l-mediated immunity, the in vitro response of bronchoalveolar lavage f luid (BALF) and peripheral blood (PB) lymphocytes (PBL) to exogenous m itogen was analysed. BALF and PBL from control (n = 9) and MVV-infecte d (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 q uantified by dual-colour flow cytometry using the bovine anti-IL-2R mo noclonal antibody IL-A111. 1L-2R expression by lymphocytes in BALF and PB from control and MVV-infected animals, with and without Con A stim ulation, were compared. In the absence of Con A stimulation, the propo rtion 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(+) lympho cytes from MVV-infected animals that expressed IL-2R remained signific antly (P < 0.05) lower than for controls. Comparisons within group sho wed that, after Con A stimulation, the proportion of all the T cell su bsets 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 significa ntly increased. In the MW-infected group, this increase was significan t (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 cont rol and MVV-infected animals induced a significant elevation in the pr oportion of all T cell subsets expressing IL-2R when compared to cultu red unstimulated control cells. However, there was considerable hetero geneity in the response to Con A of PB T cells from both groups of ani mals. 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 CD 8(+)/IL-2R(+) T cells from MVV-infected animals being significantly (P < 0.05) lower than that from controls. From these studies it can be c oncluded that the BALF T lymphocyte immune dysfunction observed during natural MVV infection, characterized by impaired IL-2R expression, is maintained under in vitro conditions.