EARLY PULMONARY CELL RESPONSE DURING EXPERIMENTAL MAEDI-VISNA VIRUS-INFECTION

A model of experimental infection with EV1, a British isolate of maedi -visna virus (MVV), has been developed. Twelve male Texel sheep were a llocated to three groups and inoculated by the respiratory route with different inocula. Six of the animals received 10(7.2) tissue culture infective dose (TCID50) of MVV EV1 strain. Two sheep were inoculated w ith the same dose of heat inactivated MVV EV1 strain. An additional gr oup of four sheep was sham-inoculated with identically prepared virus- free culture media, Experimental infection was followed for 16 weeks, Prior to inoculation, routine haematology, bronchoalveolar lavage (BAL )nd flow cytometric analysis of bronchoalveolar lavage fluid (BALF) ly mphocytes were performed in all animals to provide baseline parameters . Flow cytometric analysis of BALF lymphocytes and differential BALF c ell counts were performed. Precipitating antibodies to MVV developed i n all MW-inoculated animals during the first 4 weeks post-inoculation, while the rest remained seronegative to MVV. MW-infected animals had significantly decreased (P < 0.05) percentages of macrophages and sign ificantly increased (P < 0.05) percentages of lymphocytes in BALF 4 we eks post-inoculation. Phenotypic changes in BALF T lymphocytes from MV V-inoculated animals, compared with the other two groups. showed signi ficantly decreased (P < 0.05) percentages of CD4(+) and gamma delta(+) T lymphocytes, significantly increased (P < 0.05) percentages of CD8( +) lymphocytes and significant inversion (P < 0.05) of the CD4(+)/CD8( +) ratio at different sampling times, but between 2 and 12 weeks post- inoculation, These findings indicate that during experimental MVV-infe ction an early, short-term cellular reaction occurs in the lung, that is characterised by T lymphocyte phenotypic changes that are very simi lar, if not identical, to those observed in natural MW infection.