EFFECT OF YERSINIA-PESTIS YOPM ON EXPERIMENTAL PLAGUE

YopM of Yersinia pestis has previously been shown to be necessary for full virulence in mice and to be able to bind human alpha-thrombin. Th is activity prompted the hypothesis that YopM, functioning extracellul arly during plague, might be accessible to neutralization by antibody and hence might be a protective antigen, This study tested this hypoth esis and found that YopM was not protective, either by passive or acti ve immunization, in inbred or outbred mice. These findings showed that either YopM-specific antibody does not have access to YopM during exp erimental plague or the function of extracellular YopM is not neutrali zable by antibody. Exogenously supplied YopM partially restored virule nce to a YopM(-) strain of Y. pestis while having no effect on lethali ty of Listeria monocytogenes. These findings indicate that YopM does n ot significantly alter host defenses important for resistance against heterologous infection (Listeria monocytogenes) but raise the possibil ity that YopM has a minor extracellular function specific to homologou s infection (Y. pestis).