Mechanisms of immunity in typhus infections. VI. Differential opsonizing and neutralizing action of human typhus rickettsia-specific cytophilic antibodies in cultures of human macrophages

Abstract

Human peripheral blood monocytes were incubated in vitro for 6 days to allow time for transformation into macrophage-like cells. Cytophilic antibodies in typhus convalescent human serum were demonstrated by addition of R. mooseri or R. prowazeki to passively sensitized human peripheral blood monocyte-derived macrophages that were held at 4.degree. C. Rosettes of rickettsiae were found around macrophages sensitized with immune serum but not around macrophages incubated with normal serum. Inhibition of rosette formation occurred if the macrophages were maintained in normal human serum before addition of immune human serum. Rosettes of R. mooseri were also formed around monocytes obtained from an individual infected with R. mooseri. If the antibody-sensitized macrophages were maintained at 34.degree. C, enhanced phagocytosis of R. mooseri or R. prowazeki occurred as compared with macrophages exposed to normal human serum before infection. Cytophilic antibody did not significantly inhibit the subsequent growth of R. prowazeki within the macrophages; when R. prowazeki was mixed with immune serum before addition to the macrophage, growth of R. prowazeki was largely inhibited. The significance of antibody cytophilic for macrophages in typhus infections is discussed.