PNNL

Abstract

Ehrlichia chaffeensis is an obligatory intracellular Gram-negative bacterium and is the etiologic agent of human monocytic ehrlichiosis (HME). Although E. chaffeensis induces generation of several cytokines and chemokines by leukocytes, E. chaffeensis lacks LPS and peptidoglycan. Bioinfomatic analysis of the E. chaffeensis genome, however, predicted genes encoding fifteen lipoproteins and three posttranslational lipoprotein processing enzymes. The present study showed that using multidimensional liquid chromatography followed by tandem mass spectrometry, all predicted lipoproteins as well as lipoprotein-processing enzymes were expressed by E. chaffeensis cultured in human promyelocytic leukemia cell line, HL-60. Consistent with this observation, a signal peptidase II inhibitor, globomycin was found to inhibit E. chaffeensis infection and lipoprotein processing in HL-60 cell culture. To study in vivo E.chaffeensis lipoprotein expression and host immune responses to E. chaffeensis lipoproteins, thirteen E. chaffeensis lipoprotein genes were cloned into a mammalian expression vector.