Investigation of the role of endoplasmic reticulum stress in immune response and immune regulation

Endoplasmic reticulum (ER) is the vital organelle that contribute to protein synthesis-modification, cellular calcium storage and calcium homeostasis, and lipid synthesis. Physiological and pathological factors that disrupt ER homeostasis cause endoplasmic reticulum stress. In such cases, unfolded protein response can be initiated by the different molecular pathways within the cell. The primary purpose of the Unfolded Protein Response is to initiate transcriptional and translational programs to restore ER homeostasis for cell survival. Unfolded or misfolded proteins cause ER stress, that leads activation largely three signaling sensor proteins and consequently transmitting of signals by the 3 pathways. These sensors are ER transmembrane sensor protein (PRKR-like endoplasmic reticulum kinase (PERK), activating transcription factor 6 (ATF6) and protein 1 (IRE1) requiring inositol. The result of activation of these pathways is weakening of overall protein synthesis, but the synthesis specific proteins that should process and fold misfolded proteins. In case the chaperons cannot provide refolding, protein catabolism associated with ERAD is triggered. If these mechanisms cannot restore chronic ER homeostasis, the cells undergo apoptosis. ER stress plays an important role in the control of various intracellular physiological functions. Impaired ER stress response is associated with the disruption of adaptive immune response regulation. It is known that sensors of the expanded protein response play a role in the development, differentiation, proliferation of B and T cells and other types of immune cells, and production of cytokines and antibodies by these cells. Unfolded Protein Response activates chaperones and signal pathways in the ER to regulate ER stress in differentiated immune cells. There are studies related B cells differentiation to plasma cells, which have achieved results about previous expression of upregulated XBP1 to adapt to high levels of antibody synthesis. It was previously thought that XBP1 expression increased because of immunoglobulin synthesis and the accumulation of extended immunoglobulin chains. Subsequent studies have shown that XBP1 induction occurs in B cells prior to immunoglobulin synthesis. However, the factors underlying the activation of UPR in the early stages of plasma cell development remain unclear. Some In vitro studies showed that the expression of proteins associated with unfolded protein response during B cell differentiation, such as BiP binding-immunoglobulin protein and GRP94 expression are also changed. Immune responses mostly depend on intracellular signaling. Other studies have shown that UPR plays crucial role in T cell differentiation and DC development and maturation. Despite studies on the role of ER stress in immunity, it's role in human immunity, especially the role of ER stress in splenic follicular B cells, which play an important role in T-dependent immune responses has not been fully investigated. And how these cells affect the T cell subpopulation that they interact with, remains uninvestigated. For this reason, our task was to study the phenotypic variability of subpopulations of ER-stress-induced splenic follicular B cells. At the same time, we have sought to investigate how stress-induced ER populations will affect the variability of the phenotype of helper and regulatory T cells to express surface molecules. We have conducted studies on the variability of expression surface molecules of ER-stress-induced splenic follicular B cells and T helper cells that were co-cultivated with them. Research was started with the obtaining a cell suspension from the spleen. Then cell isolation by Magnetic Cell Isolation method from cell suspension was performed for further in vitro investigation. The next stage was the formation of cell culture. TG was used to induce ER stress in isolated B-cells. ER stress induced B cells co-cultivated with the T cell population. Flow cytometry method was used to estimate cellular immunephenotyping in cells. Keywords: ER stress, unfolded protein response, follicular B lymphocytes, follicular helper T lymphocytes, follicular T helper cells.