DIFFERENTIAL IMMUNE RESPONSES TO S. AUREUS CARRIAGE

Staphylococcus aureus is a human pathogen that is carried in the nose of 30% of the healthy population at any given time, but is also never carried by 20% of the population. The immune system presumably plays a role in determining carriage patterns. The immune response to S. aureus infection and carriage is largely unknown but Th-17 was shown to play a role in the response to Staphylococcal infections. Here, we study the T cell response to S. aureus carriage

We recruited 7 healthy individuals who were found to be S. aureus carriers in multiple screenings. S. aureus whole cell antigens were made from 1) strains isolated from their anterior nares, 2) a well-characterized virulent MRSA strain and 3) genetically similar strains from a large carriage collection. PBMCs were separated from the volunteers` blood, and stimulated with the various S. aureus whole cell antigens. Th17 and Th1 cell responses, as well as various suppressive cytokine responses were measured using real time PCR, ELISA, and FACS.

We observed that PBMCs from the carriers had significantly lower Th17 and Th1 responses to stimulation with their own S. aureus strains (endogenous strains) compared to stimulation with either USA300 or the other carrier strains (exogenous strains). IL-19 expression was found to be higher in response to a carrier`s endogenous strain. These differential responses were not seen 6 months post-carriage. Strains that were genetically similar to the endogenous strain had similar responses.

This differential immune response to an individual’s own carrier strain may play a significant role in determining S. aureus carriage.