In our previous study, by measuring serum cytokine levels in the acute and recovery stage of Japanese spotted fever (JSF), IFN-ɤ and IL-6 were proved to be the critical immunological cytokines against Rickettsia japonica (R. japonica) infection. Tularemia is an infectious disorder caused by tick biting or contact with infected animals, and is also known as rabbit fever. There have been no confirmed cases in the recent two decades in Japan. We measured serum anti Francisella tularensis (F. tularensis) IgG titer using indirect enzyme-linked immunosorbent assay (ELISA) kit in the acute and recovery stage of three patients with JSF. The result of the IgG titer was compared with the cytokine concentrations of IFN-ɤ, IL-6, IL-4, IL-5, IL-9, and IL-33, eosinophil count, and CRP quoted from our previous report. Two of three cases have anti F. tularensis IgG, and the IgG levels between acute and recovery stage were unchanged. These two cases showed low IFN-ɤ concentration and CRP, but IL-4, IL-5, IL-9, IL-33 levels and eosinophils were high compared to those in the F. tularensis IgG-negative patient. IL-6 concentration was unchanged between the three patients. Residents living in the endemic area of JSF in Mie prefecture, Japan, may have antibodies against F. tularensis, although tularemia has never been reported. The cases of having the F. tularensis antibody showed a mild inflammatory response of JSF and might skew to type 2 immunological condition even in the acute phase of JSF.
Keywords: Francisella tularensis; Rickettsia japonica; IgG; Japanese spotted fever; Tularemia.
© 2021 Japanese Dermatological Association.