Increased levels of activated leukocyte cell adhesion molecule (ALCAM)—a ligand for the costimulatory T cell receptor CD6—have previously been identified in urine of patients with lupus nephritis. New research by Chalmers et al. has validated this finding in an expanded and more diverse cohort of> 1,000 patients and demonstrated ALCAM expression by resident and infiltrating renal cells. Moreover, CD6 blockade reduced inflammation and improved outcomes in models of spontaneous lupus and immune-complex glomerulonephritis.