Mice with depleted complements, or lacking B cells, FcγR1, CR1, CR2, or Nox2 (a subunit of NADPH oxidase) are more susceptible to non-lethal dose infection with the HF strain of Ehrlichia (Ixodes ovatus Ehrlichia) that is closely related to E. chaffeensis[28]. This evidence concerns the gene CR2 and infection.