Relationships between IFNgamma, IL-6, corticosterone, and Listeria monocytogenes pathogenesis in BALB/c mice

The relationships between Listeria monocytogenes (LM) pathogenesis, based on bacterial load, and serum levels of IL-6, IFNgamma, and corticosterone (CORT) were quantified. Serum IFNgamma levels increased along with the LM burden; however, with LM burdens > or =3 x 10(6) CFU per spleen, the serum IFNgamma level decreased along with a decrease in splenic weight. Serum IL-6 levels exponentially increased with increases of LM, and the CORT level positively correlated with the increase in IL-6 and LM. The serum level of IFNgamma appeared to be a good biomarker of the host's ability to combat the infection only when the LM burden did not exceed a critical level (>3 x 10(6) CFU per spleen). Interestingly, the LM load at which the IFNgamma level began to decline was near the dose at which the IL-6 concentration exponentially increased, suggesting a transition point shift from stress (assessed as CORT level) being immunoenhancing to becoming immunosuppressive. The IL-6:IFNgamma ratio may be a good indicator of disease severity and/or the ability to cope with an infection.