Evaluation of antibody-dependent enhancement of feline infectious peritonitis virus infectivity using in situ hybridization.

Infection of primary macrophages in vitro by feline infectious peritonitis virus (FIPV) was used as a model system to study the kinetics of Fc receptor-mediated antibody-dependent enhancement (FcR-ADE) of virus infectivity at the single cell level. Cells were examined for evidence of viral RNA synthesis at various times points after infection, using 35S-labeled riboprobes and in situ hybridization. At each time point, infection of macrophages with FIPV in the presence of enhancing antiserum was compared to infection with FIPV alone. Both positive- and negative-sense FIPV RNA synthesis began at the same time point after infection in each case. In addition, the level of enhancement was the same from the earliest time of detectable RNA synthesis onward. Therefore, the degree of enhancement appears to be determined at an early point in the infection cycle. These results indicate that Fc-ADE does not induce more rapid viral RNA synthesis compared to infection with FIPV alone. Our results are compared to those of recent work concerning ADE of human immunodeficiency virus (HIV) in the presence of complement.