Serodiagnosis of human granulocytic ehrlichiosis by a recombinant HGE-44-based enzyme-linked immunosorbent assay

Current antibody testing for human granulocytic ehrlichiosis relies predomi nantly on indirect fluorescent-antibody assays and immunoblot analysis, Sho rtcomings of these techniques include high cost and variability of test res ults associated with the use of different strains of antigens derived from either horses or cultured HL-60 cells, We used recombinant protein HGE-44, expressed and purified as a maltose-binding protein (MBP) fusion peptide, a s an antigen in a polyvalent enzyme-linked immunosorbent assay (ELISA), Fif ty-five normal serum samples from healthy humans served as a reference to e stablish cutoff levels, Thirty-three of 38 HGE patient serum samples (87%), previously confirmed by positive whole-cell immunoblotting, reacted positi vely in the recombinant ELISA, In specificity analyses, serum samples from patients with Lyme disease, syphilis, rheumatoid arthritis, and human monoc ytic ehrlichiosis (HME) did not react with HGE-44-MBP antigen, except for o ne sample (specificity, 98%). We conclude that recombinant HGE-44 antigen i s a suitable antigen in an ELISA for the laboratory diagnosis and epidemiol ogical study of HGE.