The aim of this study is to investigate whether VISTA, a newly identified negative immune regulatory protein, differs in monocytes and T cells of patients diagnosed with Multiple Sclerosis (MS) and Clinically Isolated Syndrome (CIS) compared to the same cell types in healthy controls. Additionally, the potential clinical correlation of VISTA expression in the follow-up of MS and CIS patients will be examined. By elucidating the role of VISTA in the pathophysiology of MS, this study will contribute to the literature by exploring its potential as a biomarker and its relevance in the development of novel therapeutic strategies. Specifically, this study will compare VISTA protein secretion in MS patients at the time of their first attack with that of healthy controls. Furthermore, changes in VISTA protein secretion will be assessed in blood samples collected at 6- and 12-month follow-ups, and the correlations of these changes with clinical and laboratory findings will be investigated. Finally, this study aims to determine whether CD4+ and CD8+ T cells, monocytes, and T regulatory (Treg) subgroups in the first attack blood samples of MS patients exhibit similar functional properties in terms of VISTA protein secretion as their counterparts in healthy controls. To achieve this, monocytes and T cell subtypes will be stimulated, and their pro- and anti-inflammatory cytokine responses will be analyzed.