Characterization of Non-oncogenic Marek's Disease Virus-infected and Turkey Herpesvirus-infected Lymphocytes

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Abstract
Splenic leukocytes derived from N- and P-line chickens exposed to turkey herpesvirus (HVT-4), and from UCD-003 chickens exposed to the non-oncogenic SB-1 clone of Marek''s disease virus were fractionated into subpopulations at various days post-exposure. The level of infection in these fractions was determined by enumeration of plaque-forming units after co-cultivation of leukocytes with virus-permissive chicken embryo fibroblasts. At 5 days post-exposure most HVT-4-infected lymphocytes were found to be of intermediate to low buoyant density (1.040-1.065 g/ml) and not to have detectable Fc receptors. They possessed surface Ia but were not IgM-bearing. At 15 days post-exposure HVT-4-infected lymphocytes were found to be of intermediate to high buoyant density (1.070-1.080 g/ml) and, at this time, virus isolation rates (plaque-forming units/106 cells) from fractions enriched in cells bearing Fc receptors were approximately equal to those leukocyte suspensions depleted of Fc receptor-bearing cells. The percentage reduction in infectivity caused by depletion of Ia-bearing cells at 15 days post-exposure was less than that at 5 days post-exposure. At both 5 and 15 days post-exposure carbonyl Fe treatment failed to remove HVT-4-infected lymphocytes. These characteristics were similar whether HVT-4-infected lymphocytes were derived from N- or P-line chickens. SB-1-infected lymphocytes derived from UCD-003 chickens at 6, 7 and 14 days post-exposure were detected with equal frequency in fractions enriched or depleted of cells possessing Fc receptors. SB-1-infected lymphocytes for the most part lacked surface Ia and IgM, and were not depleted by carbonyl Fe treatment. Evidently, most HVT-4- and SB-1-infected lymphocytes detectable by virus isolation were neither B cells nor macrophages.