MUC4 and Keratoconjunctivitis sicca: In line with previous findings, our results revealed a significant increase in the expression of MUC4 and MMP-9 in corneal tissue exposed to the dry eye condition, suggesting that cytokine-mediated increases in the levels of MUC4 and MMP-9 could represent a physiological response to enhance the ocular surface defense against microbial stress [9].