MR1 and infection: A TRAV1-2− T cell clone (D462-E4, TRAV12-2) reacted to MR1-5-OP-RU tetramer and responded to RL-6-Me-7-OH but not RL-6,7-diMe and in addition to infection with Streptococcus pyogenes which lacks the riboflavin biosynthetic pathway, suggestive of an undefined riboflavin-independent MR1 antigen (88).