Investigation of the effect of Golgi stress on HLA-G expression on follicular T and B cell surface

The aim of thesis study is to investigate the effect of golgi stress induced by Brefeldin A treatment on the expression of MHC Class-II and non-classical HLA-G molecules in follicular B cell. We are going to investigate the impact of golgi stress of B follicular cells on HLA-G molecules expression on the cell surfaces of T follicular helper (Tfh). The immune system recognizes self and non-self antigens, and present foreign antigens to T cells through "Major Histocompatibility Complex (MHC)". MHC have been classified into four classes: class-I, II, III and IV. The primary function of MHC Class-I (HLA-A, -B, -C) and MHC Class-II (HLA-DR, -DP, -DQ) molecules is to participate in antigen presentation. Non-classical Class-I MHC (HLA-E, -F, -G) molecules are immunomodulatory molecules. Class-I HLA molecules present antigens to CD8+ cytotoxic T cells while Class-II molecules present to CD4+ hepler T cells. After B cells are activated, it can act as antigen-presenting cells by increasing the expression of MHC Class-II molecules. The MHC Class-II peptide complex is transported to the cell surface to present antigen to CD4+ T cells. Non-classical Class-I HLA-G molecules function in the modulation of the immune system Immunoglobulin-like transcript 2 (ILT2), which acts as a receptor for HLA-G, is expressed by B cells, T cells, NK cells, dendritic cells, and other immune cells. Interaction of ILT2 with its ligands suppresses the function of T and B cells. The recipient recognizes the graft tissue with the MHC molecules on its surface. The Golgi plays a central role in the uptake, processing, packaging and transport of proteins and lipids. Brefeldin A is a stress inducer for golgi. It activates the golgi stress pathways, disrupts the structure of golgi and blocks protein transport. This is an experimental study in which secondary lymphoid tissue samples (spleen samples) from 3 different individuals were used. T cells and B cells were isolated from spleen samples by magnetic bead method. T:B cell co-culture was performed and 0. hour immunophenotyping study was performed by flow cytometry method. Golgi stress was induced in B cells by treatment with Brefeldin A. Golgi stress in B cells was demonstrated by immunohistochemistry using anti-GM130 staining followed by immunofluorescence microscopy and flow cytometry to determine the change in HLA-DR expression ratio. T:B cell co-culture was performed by cell culture method and steroid treatment was applied. Changes in cell surface markers of Tfh cells and follicular B cells depending on time (6/12/24 hours), golgi stress and steroid effect in cell culture were evaluated by flow cytometry method. In B cells isolated from secondary lymphoid organs, golgi stress induced by Brefeldin A treatment decreased the expression of HLA-DR, an MHC Class-II molecule on the cell surface. Steroid treatment increased HLA-G expression on the surface of Tfh cells and B cells. Keywords: HLA-G, Follicular B cell, T follicular helper cell, Golgi stress