NPM1 and systemic lupus erythematosus: These anti-NPM antibody-positive SLE sera were analysed by immunoblotting on HL-60 cell protein separated by 2D PAGE (Fig. 5a); most of them (80%) reacted consistently with a spot of molecular mass (36 kDa) and pI (4.5) that had the same coordinates as that recognized by male WB mice and was characteristic of NPM (Fig. 5c).