A DIFFERENTIAL CELLULAR IMMUNE RESPONSE TO S. AUREUS CARRIAGE

Staphylococcus aureus is a human pathogen that is carried in the nose of 30% of healthy individuals at any given time, while it is never carried by others. The role of the immune system in carriage is unknown, but Th17 cells are known to play a role in infection and clearance.

In order to study the cellular immune response to S. aureus carriage, we recruited 12 healthy persistent S. aureus carriers. We cultured PBMCs isolated from these carriers with antigens of endogenous S. aureus strains (strains isolated from the nose of the same carrier) and exogenous strains (isolated from the nose of another carrier), as well as strains that were genetically similar to the endogenous strain. Expression, secretion, and differentiation of Th1 (IFNγ), Th17 (IL-17, RORGT), and suppressive transcription factors and cytokines (FOXP3, IL-10, IL-27, and IL-19) were measured using real time PCR, ELISA, and FACS accordingly.

The increase in IL-17 expression and secretion was significantly lower in response to endogenous strains compared to exogenous strains of S. aureus. IL-19 was found to be up‑regulated in response to endogenous strains but not exogenous ones. Addition of recombinant IL-19 to PBMCs resulted in a decreased IL-17 response compared to PBMCs cultured with medium only. Some strains that were genetically similar to the endogenous strain were able to induce a similar decreased IL-17 and increased IL-19 response as the endogenous strain. This differential tolerogenic immune response may play a role in determining S. aureus carriage patterns.