MONOCYTE FUNCTION IN CATTLE EXPERIMENTALLY INFECTED WITH BOVINE IMMUNODEFICIENCY-LIKE VIRUS

The effects of bovine immunodeficiency-like virus (BIV) on monocyte function were examined in experimentally infected cattle and in monocytes infected in vitro. Infection with the R29 isolate of BIV appeared to have relatively little effect on monocyte function in cattle during the first 2 years postinfection (PI). For the first 4 to 8 months post infection, monocyte phagocytosis of Staphylococcus aureus tended to be lower (P=0.06) in BIV infected calves than in control animals. After 8 months PI, however, phagocytosis became equal between the two groups. Random and chemotactic migration and antibody-dependent cell-mediated cytotoxicity (ADCC) did not appear to be affected by BIV infection, Monocytes from BIV infected cattle were able to respond to in vitro treatment with interferon gamma similarly to monocytes from control cattle. Although experimental infection with BIV R29 resulted in minimal effects on monocyte function, this result could have been due either to a low virus burden in vivo or because BIV is intrinsically unable to affect monocyte function, To distinguish between these possibilities, monocytes from control, uninfected cattle were treated with BIV virus in vitro. Treatment of normal monocytes with cell-free virus significantly (P<0.05) increased phagocytosis and random and chemotactic migration and decreased ADCC, in a dose-dependent manner. It appears, therefore, that the normal function of peripheral blood monocytes in the BIV R29 infected animals may be due to a low virus burden rather than to the inability of BIV to affect monocyte function. The in vitro infection results also raise the possibility that the function of monocyte derived cells at local sites of BIV replication may be altered.