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347 p. Multiple sclerosis (MS) is a chronic inflammatory neurological disease whose underlying cause remains uncertain and can be influenced by different environmental and genetic factors. We have studied two MS-susceptibility genes, IL22RA2 and IL12A, to better understand their regulation and relationship to MS. We demonstrated that the IL22RA2 gene gives rise to three isoforms in monocyte-derived dendritic cells (moDCs).. We also found that CD14++/CD16+ intermediate monocytes produced higher levels of IL22RA2 mRNA than classical and non-classical monocytes. Using transfected human cell lines, we demonstrated that the protein product of IL22RA2 variant 1 (IL22RA2v1), the IL-22BP isoform 1 (IL-22BPi1), was poorly secreted and largely retained in the endoplasmic reticulum (ER). We performed interactome analysis to uncover the mechanism underlying the ER retention of IL-22BPi1 and identified ER chaperones GRP78, GRP94, GRP170 and calnexin as main interactors. Structure-function analysis revealed that, like IL-22BPi2, IL-22BPi1 binds to the substrate-binding domain of GRP78 as well as to the middle domain of GRP94, and thus, we have demonstrated the domain of interaction of IL-22BPi1 and IL-22BPi2 with GRP78 and GRP94. Upon silencing of IL22RA2 expression in moDC, GRP78 levels were significantly reduced, suggesting that native IL22RA2 expression naturally contributes to upregulated GRP78 levels in these cells. Finally, we demonstrated that another variant apart from the canonical IL12A was expressed in moDCs and in different immune and epithelial cells lines. Altogether, our work highlights the relevance of the study of splicing variants of MS susceptibility genes for a better understanding of the effect of the genetic factors in the disease.