This study deals with the possibility that enhanced infection results in enhanced disease. Specifically, it proposes to investigate the mediation of viral infection by non-neutralizing antibody. The infection of mononuclear phagocytes by dengue virus is the prototype for this phenomenon. The ultimate research goal is to identify effector mechanisms in dengue disease and to evaluate analogous immunopathological mechanisms and effectors which might be responsible for triggering SIDS. Because dengue shock syndrome correlates with the state of immune elimination of virus infected cells, this phase of our research will focus on the immune response to dengue, using the monkey model. In view of their possible role in SIDS, respiratory syncytial and parainfluenza viruses will be studied for immunologically enhanced infection in leukocytes, in vitro.