Anaplasma phagocytophilum, an obligate intracellular pathogen that persists within polymorphonuclear leucocytes, is the second most common tick-borne agent in North America. We now show that infection of a promyelocytic cell line and neutrophils with A. phagocytophilum results in pathogen-specific tyrosine phosphorylation of ROCK1. Phosphorylation is associated with PSGL-1 and Syk, because PSGL-1 blocking antibodies and siRNA targeting Syk interfere with ROCK1 phosphorylation in A. phagocytophilum-infected cells. Knockdown of either Syk or ROCK1 also markedly impaired A. phagocytophilum infection. These data demonstrate a role for A. phagocytophilum-mediated ROCK1 phosphorylation in infection, and suggests that inhibiting this pathway may lead to new, non-antibiotic strategies to treat human granulocytic anaplasmosis.