Immune response to Yersinia outer proteins and other Yersinia pestis antigens after experimental plague infection in mice

Abstract

There is limited information concerning the nature and extent of the immune response to the virulence determinants of Yersinia pestis during the course of plague infection. In this study, we evaluated the humoral immune response of mice that survived lethal Y. pestis aerosol challenge after antibiotic treatment. Such a model may replicate the clinical situation in humans and indicate which virulence determinants are expressed in vivo. Immunoglobulin G enzyme-linked immunosorbent assay and immunoblotting were performed by using purified, recombinant antigens including F1, V antigen, YpkA, YopH, YopM, YopB, YopD, YopN, YopE, YopK, plasminogen activator protease (Pla), and pH 6 antigen as well as purified lipopolysaccharide. The major antigens recognized by murine convalescent sera were F1, V antigen, YopH, YopM, YopD, and Pla. Early treatment with antibiotics tended to reduce the immune response and differences between antibiotic treatment regimens were noted. These results may indicate that only some virulence factors are expressed and/or immunogenic during infection. This information may prove useful for selecting potential vaccine candidates and for developing improved serologic diagnostic assays.

FIG. 1

IgG response to Y. pestis antigens in mice surviving pneumonic plague. Each graph represents a separate antigen tested against individual serum samples from 12 mice treated with ofloxacin starting 42 h postchallenge. The IgG ELISA titers are the geometric mean reciprocal endpoint dilutions from three separate assays. Note differences in the scale of the abscissa. No data shown indicates that the mean for that sample was less than twofold different from normal mouse serum tested with the same antigen.

FIG. 2

Immunoblot analysis of IgG antibody response to Y. pestis protein antigens. Y. pestis antigen preparations (2.5 μg per gel) were isolated by SDS-PAGE on 10% Tris-glycine gels (Novex) and transferred to nitrocellulose membranes. All 12 serum samples from the group of mice treated 42 h postchallenge with ofloxacin were incubated overnight against each antigen at a serum dilution of 1:1000 with a Mini-PROTEAN II multiscreen apparatus (Bio-Rad). Positive reactions were visualized by ECL.