Cloning of the Gene Encoding the 44-Kilodalton Antigen of the Agent of Human Granulocytic Ehrlichiosis and Characterization of the Humoral Response

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Abstract
Antibodies in the sera of patients with human granulocytic ehrlichiosis (HGE) commonly recognize a 44-kDa antigen. We cloned the gene encoding 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-infected mice. The gene,hge-44, is part of a multigene family, with sequence similarity to theAnaplasma marginale msp-2genes. RNA-PCR studies confirmed thathge-44is expressed by aoHGE cultured in HL-60 cells and 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 sera from eight patients with HGE and in two sera from two aoHGE-infected mice bound recombinant HGE-44. Antibodies in the sera of healthy individuals or patients withEhrlichia chaffeensisorBorrelia burgdorferiinfection did not recognize HGE-44. We conclude thathge-44is a member of a multigene family and thathge-44is expressed and elicits specific antibodies during infection.