Effects of experimental immunosuppression on reovirus-induced tenosynovitis in light-hybrid chickens

Groups of SPF chicks which had been immunosuppressed either by surgical thymectomy (Tx) or surgical bursectomy (Bx) or cyclophosphamide (Cy) treatment or Tx plus Cy treatment (Tx + Cy), as well as untreated birds, were inoculated with arthrotropic avian reovirus at 1 day of age and observed for up to 5 weeks. Cy treatment with or without Tx increased the mortality, incidence of gross leg lesions and severity of microscopic lesions. The Bx group showed only an increase in mortality, and the Tx group response was similar to the untreated group. Dead birds had hepatic necrosis, which in both Cy-treated groups was associated with calcification. Surviving Cy-treated birds had acute tenosynovitis with large amounts of serous exudate in leg tendon sheaths, and a massive heterophilic but only mild lymphocytic infiltration of tendon sheaths. Tenosynovitis lesions in Bx birds were similar to those of the untreated chickens, with small amounts of yellowish brown gelatinous exudate and moderate chronic inflammatory changes in leg tendon sheaths. In Tx birds gross lesions were rarely seen and the microscopic lesions were mild. Reovirus was recovered from cloacal swabs from untreated and Tx birds for 2 weeks, Bx birds for 3 to 4 weeks, and Cy and Tx + Cy birds continuously throughout. Reovirus was isolated from tendon tissue of all Cy and Tx + Cy infected birds examined at 5 weeks after infection, and gross tenosynovitis lesions were seen in all birds. The virus was recovered from the tendons of only some of the Tx and Bx groups and more frequently from apparently normal birds. This was especially marked in the infected Tx group. Antibody responses were positive and similar in untreated and Tx birds, were delayed in the Bx group (the precipitation test only) and absent from most of the Cy and Tx + Cy birds. Thus recovery from reovirus infection probably involves both the B- and T-cell systems but the B-cell system appears to be predominantly protective..