β2 microglobulin (β2m) deficiency reduces survival and accelerates lupus nephritis in BWF1 mice. We monitored 33 β2m-/-(β2m°) (18 female and 15 male, open circles), 66 β2m+/- (30 female and 36 male, triangles) and 31 β2m+/+ (18 female and 13 male, closed circles) littermates for the development of lupus. (a) Cumulative percent survival in β2m° BWF1 mice was compared with control β2m+/- and β2m+/+ littermate mice (*P <0.01 to 0.05, log rank test). (b) Cumulative percent mice with severe proteinuria (≥300 mg/dl protein on two consecutive occasions) was increased in β2m° mice compared to control littermates (*P = 0.02 to 0.05, Fisher's exact test). Differences were more pronounced (P <0.01) when β2m° mice were compared with all controls (β2m+/- plus β2m+/+) mice. (c) Renal histological changes are expressed as the mean ± standard error of the composite kidney biopsy index and its components, glomerular activity and chronicity scores. Results from a representative experiment are shown (*P <0.05, β2m° vs control groups; n = 6 to 8 male 10-month-old mice per group, Student's t-test). (d) Representative kidney sections from these mice show severe kidney lesions with fibrosis (note increased aniline blue staining) in the glomeruli (glomerulosclerosis, GS), periglomerular region (fibrous crescent, FC) and interstitium (IF), interstitial inflammation, and large segmental lesions (SL) in β2m° mice, whereas the β2m+ mice showed relatively less advanced lesions with increased glomerular cellularity (GC) and typical immune deposits (ID, see pink-colored deposits), but minimal or no GS or IF. PAS, periodic acid Schiff.