The biologic activity of mast cell granules. VII. The effect of anti-neutrophil antibody-induced neutropenia on rat cutaneous late phase reactions.

Mast cell-dependent late phase reactions (LPR) occur in rat skin and are characterized histologically by an early (1- to 8-hr) neutrophil-rich and later (8- to 24-hr) mononuclear cell-rich infiltrate. To extend previous observations on the role of the neutrophil in the sequential histologic development of cutaneous LPR, rats were selectively depleted of circulating neutrophils using rabbit anti-rat neutrophil antibody (anti-neut), and the effects of this treatment on the histologic intensity of LPR were analyzed. In addition, the effects of neutrophil depletion on cutaneous delayed-type hypersensitivity (DTH) reactions produced by immunization with Freund's complete adjuvant followed by intradermal challenge with purified protein derivative (PPD) were assessed. Following anti-neut treatment, cutaneous DTH reactions were unaffected. In contrast, selective neutrophil depletion resulted in significant reductions in the intensity of cutaneous LPR at both 6 to 8 and 24 hr following anti-IgE or rat mast cell granule injection. Further, statistical comparison of circulating neutrophil counts with the capacity of the animal to express LPR revealed a highly significant direct correlation. These data confirm the previous observations that rat LPR are neutrophil-dependent reactions.