Retinoids and other derivatives of vitamin A are known to bear important functions in regulating differentiation and proliferation of epithelial cells (EC). We studied the effects of ATRA on colonic EC in combination with different pro-inflammatory activators. We selected the two most potent known pro-inflammatory cytokines IL-1β and TNF-α for studying the effects of ATRA. When we used these cytokines in the presence or absence of ATRA as inducers of Caco2 colonic EC cell lines we observed that ATRA was responsible for conferring the CD103 cell surface expression on DC and Mf after 6 hrs. In case of CX3CR1 cell surface expression, DC treated with ATRA-conditioned CEC supernatant showed an increase in CX3CR1 expression, whereas in Mf decreased CX3CR1 expression was observed after similar treatment. The fact that ATRA exerted different effects on different cells indicates the capability of ATRA to affect the final outcome of T-lymphocyte responses. In our in vitro system we observed that ATRA treated CEC supernatant can influence the outcome of DC responses when co-cultured with CD4+ T lymphocytes, as the balance of Th17 cells was reduced, while in Mf the number of Th17 cells was significantly increased. Defensins represent an important group of AMP consisting of 16 – 50 amino acids, organized to a structurally conserved compact organization associated with multiple functions in order to act as a first line of defense mechanism. The three subfamilies of defensins (α, β, θ) differ in their peptide length, location of disulphide bonds, their precursor structures and in the site of protein expression. Elevated levels β-defensin 3 in colonic mucosa of patients with ulcerative colitis suggest their role in the inflammatory response. In this study we have developed a targeted proteomics based method for the determination of defensin levels in cell lysates and cell culture supernatants. Human Caco2 epithelial cells were challenged with IL-1β as an inflammatory stimulus and the levels of β-defensin 2 was analyzed in cell lysates and in cell culture supernatants. The developed method was validated by using qPCR, quantitative ELISA and Western blot. The gene and protein expression levels of β-defensin 2 were significantly higher in the IL-1β treated samples as compared to the unstimulated controls. Beside β-defensin 2, the levels of β-defensin 3, β-defensin 4 and α-defensin was also measured and showed significantly higher levels in the supernatants of activated Caco2 cells. Our results show that the targeted proteomics method developed here offers an alternative approach for the mass spectrometric analyses of a selected set of defensins.