MMP9 and inclusion conjunctivitis: The statistical interaction (epistasis) observed between the risk variants within IL8 and CSF2 and the Q279R exonic SNP in MMP9, a collagenase thought to be involved in the inflammatory and scarring processes of Ct infection [11,33,34], may further suggest how genetic variation detected in IL8 and CSF2 could affect risk of trachoma: IL8, CSF2 and MMP9 are co-expressed in the Ct infected conjunctiva [34], unpublished data).