CTLA4 and focal segmental glomerulosclerosis: Urinary CD80 excretion also appears to be higher in MCD than in FSGS or other glomerular diseases [23, 24, 29, 34], and based upon these observations, we and others have hypothesized that proteinuria may involve a two-hit disorder, in which podocyte CD80 is induced by a virus or allergen but then its expression continues due to an impaired CTLA4 response [35–37].