Involvement Of MANF, A Endoplasmic Reticulum Stress-Related Protein, In Spleen Development

BACKGROUND AND OBJECTIVE:Recent studies have proved that an intact unfolded protein response (UPR) wascrucial for the immune system, especially for the development of terminallydifferentiated immunoglobulin-secreting plasma cells. Mesencephalic astrocyte-derivedneurotrophic factor (MANF; also known as arginine-rich, mutated in early tumors;ARMET), is an UPR-inducible protein and widely expressed in mammalian tissues.However, the expression profile of MANF in immune cells has not yet been explored.Owing to the abundant immunoglobulin synthesis and secretion to trigger potentiallyER stress during plasma cell differentiation, we are interested in detecting the profilesof MANF expression in the splenocytes, especially in plasma cells. To approach thisaim, we characterized the expression and cellular localization of MANF in the adultspleens. Meanwhile, the development of newborn rat spleen and the differentiation ofplasma cells were also observated.METHODS:The spleens both the patients with spleen trauma and rats with different ages andwith adjuvant arthritis were collected and observed in this study. MANF expression andits cellular localization in the spleens were observed by immunohistochemistry andimmunofluorescent labeling. T cells, B cells, plasma cells, and macrophages in the spleens were detected with the specific antibodies of anti-CD3, anti-CD20, anti-CD138and anti-CD68, respectively.RESULTS:MANF and CD68-positive cells were found to appear in the splenocytes in theearly stage of birth beginning from1wk after birth, while CD138-positive cells wereabsent at this stage. MANF was extensively distributed in the red pulp andmarginal-zone of the spleen, where CD68and CD138-positive cells locate. In addition,MANF usually localizes in the cytoplasm of normal splenocytes. Doubleimmunofluorescent staining results showed that MANF mainly localized in the plasmacells and macrophages, but not T and B cells. Furthermore, we found that BIP, CHOP,ATF6and XBP1were expressed in the MANF-positive cells. It is more interesting thatXBP1was found to be expressed in CD138-positive cells, but not CD68-positive cells.However, CHOP was expressed in CD68-positive cells, but not CD138-positive cells.CONCLUSIONS:These results suggest that MANF involves in the spleen development and immunecell differentiation, and MANF was diversely expressed under ER stress in the plasmacells, where UPR was activated.