- Properdin, a positive regulator of complement activation, is released from secondary granules of stimulated peripheral blood neutrophils. Wirthmueller, U., Dewald, B., Thelen, M., Schäfer, M.K., Stover, C., Whaley, K., North, J., Eggleton, P., Reid, K.B., Schwaeble, W.J. J. Immunol. (1997)