ANALYSIS AND ULTRASTRUCTURAL-LOCALIZATION OF EHRLICHIA-CHAFFEENSIS PROTEINS WITH MONOCLONAL-ANTIBODIES

Ehrlichia chaffeensis, an obligately intracellular bacterium with trop ism for monocytes, is the etiologic agent of human monocytic ehrlichio sis. To determine the nature and ultrastructural location of E. chaffe ensis antigens, monoclonal antibodies (MAbs) to E. chaffeensis were de veloped. The MAbs were used for immunofluorescence and Western immunob lotting analysis of the antigens of density gradient-purified ehrlichi ae. Monoclonal antibody 6Al recognized an epitope of a 30-kD protein. This antibody reacted with a strain-specific epitope of E. chaffeensis , Arkansas strain, and did not cross-react with any other ehrlichia te sted. Monoclonal antibodies 3C7 and 7Cl-B recognized Arkansas strain p roteins of 30 and 29 kD and reacted with E, chaffeensis (strain 91HE17 ) proteins of 31 and 29 kD and an E. canis protein of 30 kD. Lack of r eactivity of these two MAbs with E. sennetsu and E. risticii suggests that the epitope is group-specific. Monoclonal antibody 5D11 recognize d a 58-kD protein of both strains of E. chaffeensis as well as E. cani s, apparently a group-specific, conformation-independent epitope. Mono clonal antibody 7Cl-C reacted with 58- and 88-kD proteins of both the Arkansas and 91HE17 strains. Trypsin treatment destroyed the reactivit y of E. chaffeensis antigens with all the MAbs when tested by Western immunoblotting, indicating that these antigens are proteins with tryps in-sensitive epitopes. Immunoelectron microscopy of negatively stained intact E. chaffeensis organisms showed that the 30- and 29-kD protein s are present on the surface of the ehrlichial cell wall along with th e previously localized 28-kD protein.