The overall goal of this proposal is to characterize hematologic abnormalities in the feline acquired immunodeficiency syndrome (FAIDS) that is associated with the feline T-lymphotropic virus (FTLV) infection. FTLV is a newly described lentivirus that is structurally and biologically similar to, but antigenically distinct from, the human immunodeficiency virus (HIV). Cats infected with FTLV develop recurrent infections, diarrhea, neurological abnormalities, lymphopenia, neutropenia and anemia. We will study the interaction of FTLV and hematopoietic progenitors in vitro and in vivo. We will determine if progenitor cells (BFU-E or CFU- GM) are infected with FTLV, if they differentiate appropriately in culture, and if a serum factor or accessory cell inhibits in vitro hematopoiesis. In additional studies, cats with FTLV infection will be treated with trimethoprimsulfamethoxazole (TMP/SMX), azido-deoxythymidine (AZT) or other drugs, and we will determine the mechanism of marrow suppression should cytopenia develop. Finally, we will develop a long-term feline marrow culture system to study the interactions of progenitors, FTLV, and/or drugs in vitro. Our intent is to establish an animal model of the hematologic abnormalities in AIDS. Because blood and marrow samples can be obtained repeatedly from, cats, our model should allow prospective and longitudinal studies. In addition, as FTLV does not infect human cells or cell lines, these studies involve less biohazard than cell culture studies with blood or marrow from AIDS patients.