Regression of feline immunodeficiency virus infection.

Regression of feline immunodeficiency virus (FIV) infection was observed in seven of nine vertically infected kittens born to two chronically infected mother cats. Both provirus and nonmaternal FIV antibody were detected in all kittens by 4 weeks of age but only three of the seven kittens were positive by blood mononuclear cell coculture. Between 10 and 14 months of age blood mononuclear cells from each of the seven cats were negative at least once by polymerase chain reaction (PCR), but evidence of virus infection was detected by coculture and/or PCR in biopsied lymph node or bone marrow from five of the seven cats. Despite this evidence of persistent tissue provirus, antibody production did not persist in any of the cats beyond 1 year of age. All seven cats remained asymptomatic although CD4 and CD8 T cell counts were in the low normal range throughout the study. By contrast, two additional perinatally infected littermates that were persistently virus isolation positive developed rapid CD4 depletion and progressed to terminal immunodeficiency by 9 weeks of age. Thus FIV infection can be downregulated and/or sequestered to extremely low levels barely detectable with the assays available, although absolute clearance of virus may not occur. These observations are relevant to human immunodeficiency virus (HIV) infection in paralleling both the apparent "regression" of HIV infection reported in some perinatally infected infants and the low-level, apparently stable, infection established by attenuated simian immunodeficiency viruses.

Mucosal transmission of cell-associated and cell-free feline immunodeficiency virus.

Mucosal infection by feline immunodeficiency virus (FIV) was assessed via a single exposure of the vaginal or rectal mucosa to either infectious peripheral blood mononuclear cells (PBMCs), infectious plasma, or cell-free cultured virus. All cats inoculated with cell-free cultured virus (100 or 400 TCID) and 9 of 10 cats inoculated with infected PBMCs (2 x 10(7) or 2 x 10(5)) became persistently viremic within 3 weeks. Neither cat inoculated with 2 x 10(3) PBMCs became viremic. Rectal and vaginal exposure were equally effective routes to induce viremia. CD4+ T cells and mitogen-stimulated PBMC proliferation declined in all infected cats. However, a transient PBMC proliferative response to FIV p24gag occurred in most virus-exposed cats, especially those that did not develop detectable infection. FIV was not transmitted by mucosal exposure to infectious virus in plasma (100 TCID), a dose > 10-fold that needed for infection by parental injection. In vitro studies suggested that a plasma heat-stable virus-neutralizing factor may be associated with failure of plasma virus to establish infection via the mucosal route. Mucosal FIV infection provides a new model with which to study early stages of infection and intervention in transmucosal lentivirus infections.

Malignant histiocytosis in a domestic cat: cytomorphologic and immunohistochemical features.

Malignant histiocytosis (MH) was diagnosed in a 13-year-old neutered male Domestic Shorthair cat on the basis of light microscopic and immunohistochemical findings. Thoracic fluid analysis showed a modified transudate which contained a very few atypical discrete cells. Cytologic and histologic evaluation of mediastinal and splenic masses revealed a pleomorphic population of large, discrete, round cells 10 to 30 micrometers in diameter with marked cellular atypia. Nuclei were oval to reniform, often with prominent, bizarre nucleoli. Multinucleated cells and mitotic figures were commonly seen. Erythro- and leucocytophagia were noted. Immunohistochemistry indicated a scattered positive staining pattern with the histiocytic antigenic marker Mac387 and a minor population of cells showing positive reactivity for lysozyme. This report describes the characterization of MH in a cat and emphasizes that MH should be considered as a differential diagnosis in proliferative disorders of discrete-cells in this species.