Differential expression of the p44 gene family in the agent of human granulocytic ehrlichiosis.

Using reverse transcription-PCR targeting of the p44 genes of the agent of human granulocytic ehrlichiosis (HGE) with primers flanking the hypervariable region, we show differential expression in a murine model of HGE infection and during tick transmission. The p44 genes were differentially expressed in salivary glands of infected nymphal ticks removed during transmission feeding but not in nonfeeding infected ticks. Similarly, the p44 genes were differentially expressed in infected C3H mice, in SCID mice, and in cultured HGE bacteria. Thus, differential p44 expression exists in vivo and in vitro and could provide a basis for antigenic variation.