A novel protein of rat neutrophils (NDP): its use in estimating the neutrophil content of solid tissues

A protein has been isolated from rat neutrophils which does not appear to be present in other rat cells. This protein, which we have called neutrophil-derived protein or NDP, is confined to the cytosol of the cell and we estimate that it constitutes at least 6% of the total protein of the neutrophil. The native molecule is a cationic protein (pI approximately 9) of mol. wt 34-36,000 daltons that on SDS-PAGE yields two subunits of 10,000 and 13,000 daltons. The NDP does not bind lectins, is protease-resistant and strongly antigenic in the rabbit. Its behaviour on electrophoresis in agar and agarose show unusual features which may be relevant to other cationic proteins. NDP does not appear to correspond to any of the hitherto characterized neutrophil proteins and the only activity so far detected is a reaction of the protein with rat plasma (but not serum). Using simple immunological methods we have determined the concentration of NDP in various tissues of the rat to obtain an estimate of their neutrophil content. In addition, the NDP content in various body fluids has been determined. A similar protein to the rat NDP has been detected in the mouse.