MR1 and susceptibility to pneumonia measurement: To better understand the relationship between MR1/5-OP-RU tetramer staining, CDR3α usage and MR1-dependent T cell activity, we sorted MR1/5-OP-RU positive cells from the BAL of an available individual with non-TB pneumonia and performed limiting dilution cloning using anti-CD3 and IL-2 stimulation.