CLONING OF THE GENE ENCODING THE 44-KILODALTON ANTIGEN OF THE AGENT OF HUMAN GRANULOCYTIC EHRLICHIOSIS AND CHARACTERIZATION OF THE HUMORAL RESPONSE

Antibodies in the sera of patients with human granulocytic ehrlichiosi s (HGE) commonly recognize a 44-kDa antigen. We cloned the gene encodi ng the 44-kDa protein of the agent of HGE (aoHGE) by probing an aoHGE lambda ZAP II genomic DNA expression library with sera from aoHGE-infe cted mice. The gene, hge-44, is part of a multigene family, with seque nce similarity to the Anaplasma marginale msp-2 genes. RNA-PCR studies confirmed that hge-44 is expressed by aoHGE cultured in HL-60 cells a nd by aoHGE during murine infection. Recombinant HGE-44, expressed and purified as a glutathione transferase fusion protein, was used as the substrate in immunoblots to help diagnose HGE. Antibodies in eight se ra from eight patients with HGE and in two sera from two aoHGE-infecte d mice bound recombinant HGE-44. Antibodies in the sera of healthy ind ividuals or patients with Ehrlichia chaffeensis or Borrelia burgdorfer i infection did not recognize HGE-44. We conclude that hge-44 is a mem ber of a multigene family and that hge-44 is expressed and elicits spe cific antibodies during infection.