Correspondingly, tear fluid enhanced activation of NFkB and AP-1 transcription factors in response to bacterial antigens, and upregulated epithelial-derived innate defense genes. The latter included genes encoding RNase7 and ST2, both of which reduced bacterial internalization by corneal epithelial cells. RNase7 is a potent antimicrobial peptide, active against a broad range of bacterial pathogens, that was originally identified from the stratum corneum of human skin. Keratinocytes are the major source of this secreted innate defense protein in human skin. RNase7 has been shown to be present in other epithelia in different organ systems including the respiratory, urinary and gastrointestinal tracts, and the eye. While RNase7 is constitutively expressed in these tissues, it can also be upregulated in response to various stimuli including proinflammatory cytokines and microbial antigens. ST2, on the other hand, has been shown to have an immunomodulatory role in innate defense, e.g. negative regulation of IL-1 receptor and TLR-4 receptor signaling. ST2 is constitutively expressed in the corneal epithelium, and its immunomodulatory role is important for resolution of P. aeruginosa corneal infections in murine models by promoting Th2-mediated immune responses. The aim of the present study was to further elucidate the mechanisms by which tear fluid modulates epithelial cell susceptibility to P. aeruginosa internalization, and the relationship to RNase7 and ST2 gene expression. Since epithelial cells become exposed to tear fluid when they reach the ocular surface through a process of exfoliation, the induction of resistance to microbes would need to be rapid. The hypothesis tested was that tear fluid effects on epithelial cells involve the induction of microRNA expression to modify innate defense gene responses to bacterial challenge. MicroRNAs are small, 20- to 24 nucleotide, noncoding RNAs found in diverse organisms, which bind partially to the 3’UTR of their target mRNA to post-transcriptionally silence the target gene. These endogenous, silencing RNAs play important roles in cell and tissue development and differentiation, cell signaling and migration, cellular stress responses, and resistance to bacterial virulence via gene suppression. Moreover, microRNAs have been shown to play a role in modulating expression of innate defense genes including Toll-like receptors, their adaptor proteins, downstream signaling pathways, and transcription factors. Since numerous microRNAs are expressed at the ocular surface, microarray analysis was performed to determine which microRNAs were differentially regulated in corneal epithelial cells by bacterial antigens with and without tear fluid exposure. The results showed a selective and specific up- and down-regulation of four types of miR in tear fluid treated cells, of which miR-762 showed the AbMole Butylhydroxyanisole greatest upregulation. A combination of antagomir and microRNA mimic was then used to show that tear-induced miR-762 negatively regulates RNase7 and ST2 gene expression in corneal epithelial cells. Since expression of these two factors, which inhibit bacterial internalization, is also upregulated by tears, the data suggest that other tear-induced mechanisms must antagonize the inhibitory effects of miR-762 in regulating epithelial resistance to bacterial challenge. The results of this study show that mucosal fluid can influence epithelial microRNA expression to regulate expression of innate defense genes.