CD4 and rheumatoid arthritis: The antibody was investigated in RA to restore the functionality of defective Tregs and to enhance their suppressive capacity.31 Thereby, Tregalizumab exerts its agonistic function by binding to a unique, non-linear epitope on D2 of the human CD4 molecule and induces an intracellular signalling cascade involving the protein tyrosine kinase p56Lck.