Analysis of hematopoietic and lymphopoietic tissue during a regenerative aplastic crisis induced by avian retrovirus MAV-2(O).

Infection of 10-day-old chickens with an avian osteopetrosis virus resulted in a severe regenerative aplastic crisis. Hematopoietic and lymphopoietic tissues of chickens infected with myeloblastosis-associated virus (of subgroup B, inducing osteopetrosis, MAV-2(O] were analyzed for integrated and unintegrated viral DNA sequences, cell population shifts, weight changes, and morphological alterations. By 6 days postinfection (p.i.), DNA from bone marrow cells and peripheral blood leukocytes (PBL) contained between 0.50 and 0.70 copies of viral DNA per haploid genome. Erythrocytes and splenic leukocytes contained less than 0.10 copies/haploid genome. Granulocytes and precursor mesomyelocytes were absent from bone marrow, but numbers of erythrocytes, erythroblasts, and reticulocytes were normal. By 9 days p.i., bone marrow was severely hypoplastic and both granulopoietic and erythropoietic colonies were depleted. By 12 days p.i., erythrocytes and granulocytes were maximally depressed in peripheral blood and the amount of integrated virus in bone marrow and PBL decreased to less than 0.20 copies/haploid genome. In contrast, erythrocytes contained integrated viral DNA of up to 0.30 copies/haploid genome, indicating infection of erythrocyte precursors. At 18 days p.i., viral DNA was detected only in erythrocytes. Unintegrated viral DNA was not detected in any organs. Anemia was accompanied by splenomegaly and erythrophagocytosis. Viral DNA was never detected in thymus or bursa. Differential counting and flow cytometry of cells from bursa, thymus, and spleen, and of blood lymphocytes did not detect significant population shifts. These results suggest that MAV-2(O) infection of immunocompetent chickens occurs primarily in myelopoietic tissues, and tissues are selectively infected.