Abstract
Human immunodeficiency virus infection is characterized by a progressive decline in the number of peripheral blood CD4(+) T lymphocytes, which finally leads to AIDS. This T-cell decline correlates with the degree of in vitro-induced lymphocyte apoptosis. However, such a correlation has not yet been described in feline AIDS, caused by feline immunodeficiency virus (FIV) infection. We therefore investigated the intensity of in vitro-induced apoptosis in peripheral blood lymphocytes from cats experimentally infected with a Swiss isolate of FIV for 1 year and for 6 years and from a number of long-term FIV-infected cats which were coinfected with feline leukemia virus. Purified peripheral blood lymphocytes were either cultured overnight under nonstimulating conditions or stimulated with phytohemagglutinin and interleukin-2 for 60 h. Under stimulating conditions, the isolates from the infected cats showed significantly higher relative counts of apoptotic cells than did those from noninfected controls (1-year-infected cats, P = 0.01; 6-year-infected cats, P = 0.006). The frequency of in vitro-induced apoptosis was inversely correlated with the CD4(+) cell count (P = 0. 002), bright CD8(+) cell count (P = 0.009), and CD4/CD8 ratio (P = 0. 01) and directly correlated with the percentage of bright major histocompatibility complex class II-positive peripheral blood lymphocytes (P = 0.004). However, we found no correlation between in vitro-induced apoptosis and the viral load in serum samples. Coinfection with feline leukemia virus enhanced the degree of in vitro-induced apoptosis compared with that in FIV monoinfected cats. We concluded that the degree of in vitro-induced apoptosis was closely related to FIV-mediated T-cell depletion and lymphocyte activation and could be used as an additional marker for disease progression in FIV infection.
Highlights
Human immunodeficiency virus infection is characterized by a progressive decline in the number of peripheral blood CD4؉ T lymphocytes, which leads to AIDS
We investigated the intensity of in vitroinduced apoptosis in peripheral blood lymphocytes from cats experimentally infected with a Swiss isolate of feline immunodeficiency virus (FIV) for 1 year and for 6 years and from a number of long-term FIV-infected cats which were coinfected with feline leukemia virus
For some time it has been known that FIV infection leads to the loss of T helper cells [2] and that coinfection with feline leukemia virus (FeLV) enhances this effect [8]
Summary
Human immunodeficiency virus infection is characterized by a progressive decline in the number of peripheral blood CD4؉ T lymphocytes, which leads to AIDS This T-cell decline correlates with the degree of in vitro-induced lymphocyte apoptosis. Such a correlation has not yet been described in feline AIDS, caused by feline immunodeficiency virus (FIV) infection. The degree of HIV-induced apoptosis correlates with the T-helper cell decline and disease progression [19, 40] Such a relationship has not yet been described for FIV. The aim of the present study was to compare the degree of in vitro-induced lymphocyte apoptosis in FIV-infected cats with normal and decreased T-helper cell counts. This coinfection is known to accelerate the progression toward feline AIDS [23] by an unknown mechanism [8]
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