Effect of Antibody on the Rickettsia-Host Cell Interaction

Abstract

A recent study demonstrated that polyclonal antibodies to Rickettsia conorii and monoclonal antibodies to outer membrane proteins A (OmpA) and B (OmpB) provided effective, Fc-dependent, passive immunity, even in severe combined immunodeficient mice with an established infection. In order to determine the mechanism of protection, mouse endothelial and macrophage-like cell lines were infected with R. conorii that had been exposed to polyclonal antibodies, monoclonal antibodies to OmpA or OmpB, Fab fragments of the polyclonal antibodies, or normal serum or that were left untreated. At 0 h, Fc-dependent antibody enhancement of R. conorii adherence to endothelial and macrophage-like cell lines was inhibited by the presence of normal serum, suggesting Fc receptor-mediated adherence of opsonized rickettsiae. At 3 h, the opsonized rickettsiae had been internalized. After 72 h, inhibited survival of rickettsiae exposed to polyclonal antibodies or monoclonal antibodies to OmpA or OmpB was evident compared with growth of untreated and normal serum-treated and polyclonal Fab antibody-treated R. conorii. Polyclonal antibodies and an anti-OmpB monoclonal antibody inhibited the escape of R. conorii from the phagosome, resulting in intraphagolysosomal rickettsial death. At 48 h of infection, rickettsicidal activity of macrophages by opsonized rickettsiae was inhibited by N G -monomethyl-L-arginine, superoxide dismutase, mannitol, or supplemental L-tryptophan, and endothelial rickettsicidal activity against opsonized rickettsiae was inhibited by N G -monomethyl-L-arginine, superoxide dismutase, catalase, or supplemental L-tryptophan. Thus, Fc-dependent antibodies protected against R. conorii infection of endothelium and macrophages by opsonization that inhibited phagosomal escape and resulted in phagolysosomal killing mediated by nitric oxide, reactive oxygen intermediates, and L-tryptophan starvation.

Two Protein Lysine Methyltransferases Methylate Outer Membrane Protein B from Rickettsia

“…Proteins were obtained by slow dialysis at stepwise, decreasing concentrations of urea. SET7 methyltransferase and the histone peptide substrate H3 (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) were from New England Biolabs. N,N=-diallyltartardiamide (DATD) was from Bio-Rad.…”

“…Unlike the ␣-helical transmembrane proteins in plasma membranes, the autotransporter domains of these outer membrane proteins have structural characteristics of ␤-barrel integral membrane proteins (3, 33). As the immunodominant antigenic surface protein, native OmpB induces strong humoral and cellular immune responses in animal models and in patients (6,12,15,16,23). Methylation of OmpA of Rickettsia canadensis and ompB of Rickettsia typhi is known, but whether this is important for any other pathogenic rickettsia is unknown.…”

Differential Interaction of Dendritic Cells withRickettsia conorii: Impact on Host Susceptibility to Murine Spotted Fever Rickettsiosis

“…Ultrathin sections were cut on a Sorvall MT-6000 ultramicrotome (RMC, Tucson, AZ) and examined in a Philips 201 transmission electron microscope (Philips Electron Optics, Eindhoven, The Netherlands) at 60 kV. As a control, the subcellular rickettsial localization within BMDCs was compared to that detected in endothelial cells (the main target cells for Rickettsia) prepared and infected with rickettsiae as described previously (13,39). For each sample, approximately 100 cells were examined.…”

Rickettsial Infections in Southeast Asia: Implications for Local Populace and Febrile Returned Travelers

“…44 Antibodies against rickettsial lipopolysaccharides are also produced but they do not appear to confer any protection. 45 …”