IFNB1 and infection: Given that the concentration of IFN-β induced by BMDMs infected with O. tsutsugamushi Boryong strain, belonging to the Karp genogroup (47), is ~30 pg/ml (Figure 1C, its concentration in plasma of infected mice was always below detection limit throughout the infection period) and 1 IU/ml of type I IFNs generally equals a few pg/ml range (48), physiological levels of type I IFNs induced by O. tsutsugamushi infection may not be sufficient to inhibit its replication in vitro and in vivo.