Induction of cytokine production by different staphylococcal strains

In light of the important role of cytokines in the pathogenesis of bacterial infections, we analyzed the cytokine production induced by different Staphylococcus aureus (S. aureus), S. epidermidis and S. saprophyticus strains in human mononuclear cells (MNCs). MNCs secreted high amounts of interleukin-1beta (IL-1beta) and IL-6 proteins in responses to stimulation with all three species of Staphylococci. Interestingly, a large majority of the S. aureus strains induced significantly higher IL-12 and interferon (IFN) titers than did the S. epidermidis and S. saprophyticus strains. The RNase protection assay revealed high increases in IL-1alpha, IL-1beta, IL-1 receptor antagonist, IL-6 and IL-12 p40 transcript levels in MNCs stimulated with Staphylococci. All of the tested Staphylococcal strains proved highly efficient in mediating the induction of these genes. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis indicated considerable increases in IFNA transcript levels in MNCs stimulated with S. aureus strains, while only a very weak expression was stimulated by S. epidermidis and S. saprophyticus. These results confirm that heat-killed Staphylococci exert strong immunomodulatory effects, and suggest that the contribution of T-helper 1 (Th-1) cells to the immune response may be much extensive in infections caused by S. aureus strains, due to their high IL-12 p70 and IFN-alpha-inducing activities.