TYK2 and multiple sclerosis: In this regard, a coding variant in ﻿TYK2, which has a protective effect in multiple sclerosis (MS), AS, ulcerative colitis (UC) and Crohn’s disease, leads to a weaker response of CD4 + T helper 1 and 17 type cells to proinflammatory signals [6], which suggested that reducing the activity of TYK2 could be a potential therapeutic option for these diseases.