Relationship of lymphoid lesions to disease course in mucosal feline immunodeficiency virus type C infection

Feline immunodeficiency virus (FIV) infection typically has a prolonged and variable disease course in cats, which can limit its usefulness as a model for human immunodeficiency virus infection. A clade C FIV isolate (FIV-C) has been associated with high viral burdens and rapidly progressive disease in cats. FIV-C was transmissible via oral-nasal, vaginal, or rectal mucosa l exposure, and infection resulted in one of three disease courses: rapid, conventional/slow, or regressive. The severity of the pathologic changes pa ralleled the disease course. Thymic depletion was an early lesion and was c orrelated with detection of FIV RNA in thymocytes by in situ hybridization. The major changes in thymic cell populations were depletion of p55+/S100dendritic cells, CD3- cells, CD4+/CD8- cells, and CD4+/CD8+ cells and incre ases in apoptosis, CD45R+ B cells, and lymphoid follicles. In contrast to t hymic depletion, peripheral lymphoid tissues often were hyperplastic. Mucos ally transmitted FIV-C is thymotropic and induces a spectrum of lymphoid le sions and disease mirroring that seen with the human and simian immunodefic iency virus infections.