ENHANCEMENT OF RETICULOENDOTHELIOSIS VIRUS-INDUCED BURSAL LYMPHOMAS BY SEROTYPE-2 MAREKS-DISEASE VIRUS

The effect of serotype 2 and 3 Marek's disease virus (MDV) vaccines on the pathogenesis of reticuloendotheliosis virus (REV)-induced bursal and non-bursal lymphomas was examined in chickens of RPRL lines 15I(5) X 7(I) and 6(3) X O, respectively. At hatch, chickens were vaccinated with strain 301B/1 of serotype 2 MDV or strain FC126 of turkey herpes virus (HVT), a serotype 3 MDV and inoculated with spleen necrosis viru s (SNV), a non-defective strain of REV. In another experiment, bursas from 14-week-old 15I(5) x 7(1) chickens coinfected with strain 301B of serotype 2 MDV and SNV strain of REV at hatch were examined microscop ically for REV-induced transformed follicles by methyl green pyronin s tain and for the presence of MDV by in situ hybridization. The inciden ce of REV-induced bursal lymphomas was significantly higher in 15I(5) x 7(1) chickens vaccinated with serotype 2 MDV than in unvaccinated ch ickens or chickens vaccinated with HVT. On the other hand, the inciden ce of REV induced nonbursal lymphoma in chickens of line 6(3) x 0 vacc inated with serotype 2 MDV was comparable to that in unvaccinated chic kens or chickens vaccinated with HVT. The average number of hyperplast ic follicles in bursas from REV-infected 15I(5) X 7(1) chickens was si gnificantly higher in chickens vaccinated with serotype 2 MDV than tha t in unvaccinated chickens or chickens vaccinated with HVT, and the MD V was more frequently detected in REV-transformed than in untransforme d bursal follicles. Data from this study suggest that serotype 2, but not serotype 3, of MDV may enhance the development of REV-induced burs al lymphomas, and that neither serotype 2 nor serotype 3 MDV influence the development of REV-induced nonbursal lymphomas. The data also sug gest that the enhancement effects of serotype 2 MDV on REV bursal lymp homas may be at the stage of formation of hyperplastic or transformed bursal follicles.