Effects of HIV-1Tg serum on MOR expression in F344 rats. Peritoneal macrophages were isolated from six F344 control rats, and treated with either heated HIV-1Tg rat serum (20%), recombinant gp120 protein (1 nM), LPS (10 μg/ml), gp120 monoclonal antibody alone, heated HIV-1Tg rat serum (20%) plus gp120 monoclonal antibody, or control vehicle (culture medium) for 18 h at 37°C. The cells were harvested for total RNA isolation, and MOR mRNA levels were determined by real-time RT-PCR analysis. n = 3; *, P < 0.05 compared to control vehicle.