The present disclosure relates to methods for treatment and prevention of disease conditions mediated by T-helper 17 (Th17) and/or T-helper 1 (Th1) T lymphocytes (T cells). In particular, the present disclosure relates to use of anti-CD6 antibody for treatment of disease conditions mediated by auto-reactive Th17 and Th1 T lymphocytes. The methods of the present disclosure further have utility in methods for modulating an immune response by suppressing production of the cytokine IL-23R, thereby decreasing inflammation mediated by Th17 cells.