Immune reactions and immunopathologic changes induced in ovine fetuses and lambs by maedi-visna virus

Seventy- to 80-day fetuses of Merino ewes were inoculated intramuscularly in utero and 2-week-old lambs of the same breed intratracheally with 10(6.3) TCID50/0.1 ml of maedi-visna virus strain K1512 isolated in Iceland. While no precipitins appeared in the serum of fetuses, such antibodies were demonstrable in the lambs from postinoculation (PI) day 30. Indirect immunofluorescence (IIF) revealed the presence of antibodies in samples from both fetuses and lambs; the detectability of these antibodies, however, varied even within a given animal during the experiment. The serologic results were inversely proportional to the kinetics of circulating immune complex (cIC) production. By the lymphocyte stimulation test (LST), the blastogenic transformation of lymphocytes as measured by 3H-TdR incorporation was 6-8% and 6-14% in the fetuses and lambs, respectively. By antibody-dependent cell-mediated cytotoxicity (ADCC) test, cytotoxic capacity (10-14%) was only demonstrable in lambs inoculated at 2 weeks of age, in the 2nd month of life. Histologic examination showed that in the lungs of both fetuses and lambs lympho-histiocytic infiltration developed from PI week 4. This was later joined by lymphoid hyperplasia in the peribronchial lymph nodes. T lymphocyte proliferation was dominant in these lesions as shown by a histochemical procedure (alpha-naphthyl-acetate-esterase, ANAE). By immunofluorescence (IF), deposited immune complexes (IC) were demonstrable in various organs (wall of cerebral ventricles, endothelium of blood vessels of the brain stem, cerebellum, lungs, kidneys). These IC may play an important role in the pathogenesis of maedi-visna.