TNF and systemic lupus erythematosus: In order to determine the association of TNFA promoter polymorphism and lupus nephritis (LN), we classified genotype and allele frequencies according to the outcome variable LN, defined as fulfilling the ACR classification criteria for the renal manifestation of SLE (persistent proteinuria > 0.5 g per day or greater than 3+ by dipstick, and/or cellular casts) or evidence of LN on kidney biopsy [28].