ANTIGENIC DIVERSITY OF GRANULOCYTIC EHRLICHIA ISOLATES FROM HUMANS INWISCONSIN AND NEW-YORK AND A HORSE IN CALIFORNIA

The agent of human granulocytic ehrlichiosis (HGE), Ehrlichia phagocyt ophila, and Ehrlichia equi are very similar. HGE is of variable severi ty. Genetic and antigenic differences among 3 human isolates (Webster, Spooner, and NY-8) and 1 horse isolate (MRK) were evaluated. The 16S rRNA gene sequences were identical in all human isolates. By use of 5 homologous antisera from these 3 humans and I horse and an additional 5 antisera in heterologous reactions, the immunodominant antigens of e ach isolate were noted to differ in molecular size: 43 kDa in the Webs ter (Wisconsin) isolate, 46 kDa in the Spooner (Wisconsin) isolate, 42 and 45 kDa in the NY-8 (New York State) isolate, and a 42 kDa doublet in the E. equi MRK isolate from California. Two sera from a Wisconsin patient reacted weakly or not at all with the NY-8 isolate. Antigenic structural diversity exists among otherwise indistinguishable granulo cytic ehrlichial isolates.