In 1992, Klebanoff and coworkers [11] showed that stimulated polymorphonuclear (PMN) cells released an unknown factor which neutralized HIV-1. PMN from patients with hereditary myeloperoxidase (MPO) deficiency indicated that the antiviral activity was correlated with the presence and the release of the enzyme into cell culture medium. Adding MPO to PMN-(MPO-deficient) cell cultures restored the ability to block HIV-1 infection [11, 12] . In addition to MPO, the presence of two other factors, H 2 O 2 and chloride, was absolutely necessary to observe the antiviral activity in cell culture supernatants of stimulated PMN cells. Since the enzyme MPO catalyzes the reaction between H 2 O 2 and chloride to generate HOCl (bleach), Klebanoff and coworkers [12] suggested that this product of the MPO/H 2 O 2 /halide system was directly responsible for HIV inactivation. A clue as to the substrate of the MPO/H 2 O 2 /halide system was provided by the detection of HOCl-modified proteins in human tissue by a specific monoclonal antibody (clone 2D10G9) [13] . This antibody recognized an HOCl-modified protein in glomerular and tubulointerstitial inflammatory and fibrotic lesions and its binding was inhibited by HOCl-modified human serum albumin (mHSA) [14, 15] .