An avian, oncogenic retrovirus replicates in vivo in more than 50% of CD4+ and CD8+ T lymphocytes from an endangered grouse

Reoccurring infection of reticuloendotheliosis virus (REV), an avian oncogenic retrovirus, has been a major obstacle in attempts to breed and release an endangered grouse, the Attwater's prairie chicken (Tympanicus cupido attwateri). REV infection of these birds in breeding facilities was found to result in significant decreases in the CD4+ and increases in the CD8+ lymphocyte populations, although experimental infection of birds resulted in only increases in the CD8+ lymphocytes. Because our indirect immunofluorescent assay readily detected infection of both CD4+ and CD8+ lymphocytes, a triple labeling flow cytometric procedure was developed to quantify the individual lymphocytes infected in vivo with REV. Lymphocytes were gated with a biotinylated pan-leukocyte marker bound to streptavidin R-PE-Cy5. Chicken CD4 or CD8 specific mouse MAb directly labeled with R-PE identified the phenotype and with permeabilizing of cells, infection was indirectly labeled with rabbit IgG specific for the REV gag polypeptide and FITC conjugated goat anti-rabbit antibody. More than 50% of the total lymphocytes and of the total CD4+ or CD8+ lymphocytes supported in vivo viral expression in all infected birds examined. Remarkably, this level of infection was detected in the absence of visible clinical signs of illness.