Multiple p44 genes encoding major outer membrane proteins are expressed inthe human granulocytic ehrlichiosis agent

Human granulocytic ehrlichiosis (HGE) is caused by infection with an obliga tory intracellular bacterium, the HGE agent. We previously cloned a gene en coding HGE agent 44-kDa major outer membrane protein and designated it p44, In this study, we (i) identified five different mRNAs that are transcribed from p44-homologous genes in the HGE agent cultivated in HL-60 cells; (ii) cloned genes corresponding to the mRNAs from the genomic DNA of the HGE ag ent; (iii) showed that the genes being expressed were not clustered in the HGE agent genome; (iv) estimated that a minimum copy number of the p44-homo logous genes in the genome is 18; (v) detected two different P44-homologous proteins expressed by the HGE agent; and (vi) demonstrated existence of an tibodies specific to the two proteins in sera from patients with HGE. These findings showed that p44 multigenes have several active expression sites a nd the expression is regulated at transcriptional level, suggesting a poten tially unique mechanism for generating the diversity in major antigenic out er membrane proteins of the HGE agent. Characterization of p44-homologous g enes expressed by the HGE agent in a tissue culture would assist in underst anding a role of the p44 multigene family in pathogenesis and immune respon se in HGE.