IFNG and Rickettsiosis: Activation of TCD4+IFN-γ+ and TCD8+IFN-γ+ lymphocytes has been demonstrated in co-cultures of cells from patients infected with R. rickettsii, R. typhi and R. felis species, and in co-cell cultures from healthy donors, stimulated with the Rickettsia vaccine candidate pVAX1-OmpB24, respectively, together with the involvement of PD1 expression in the inhibition of TCD4+ and TCD8+ lymphocytes after Rickettsia infections