Biologic properties of LTB4 and paf-acether in vivo in human skin

Using an improved skin chamber technique, the consequences of prolonged contact of leukotriene B4 (LTB4) and platelet-activating factor (paf-acether) with human dermis were evaluated quantitatively and kinetically in vivo. Leukocyte chemotaxis, histoenzymologic alterations, and modifications in vascular permeability were studied in two sets of experiments. In a first set of experiments, the dose-effect relationship of LTB4 and paf-acether on leukocyte migration was studied. LTB4 (3 X 10(-8) M to 9 X 10(-7) M) in Hanks' balanced salt solution (HBSS) elicited an intense dose-dependent and time-dependent neutrophil migration. Paf-acether, at the same concentration range, induced a significant increase in cell migration only at 9 X 10(-7) M and when diluted in HBSS containing 0.25% serum albumin (HBSS-BSA). Histoenzymologic analysis demonstrated that LTB4 in vivo induced degranulation of most of the neutrophils migrating through the dermis. Paf-acether caused mild degranulation of neutrophils and induced the appearance of degranulated basophils in dermal vessels. A second set of experiments was designed to study simultaneously the modifications in vascular permeability and cell migration induced by LTB4 and paf-acether, with or without prostaglandin E2 (both at a concentration of 3 X 10(-7) M in HBSS). Since spontaneous protein diffusion in HBSS progressively declined up to a plateau reached after 20 h (1.2 +/- 0.15 mg of proteins/cm2/2 h), these experiments were carried out after a 20-h equilibration period. Leukotriene B4 induced a late and slight increase in vascular permeability. Paf-acether did so intensely and transiently. Prostaglandin E2 significantly enhanced protein diffusion and neutrophil migration induced by LTB4 and, to a lesser extent, by paf-acether. Interestingly, despite the reintroduction into the skin chambers of freshly prepared solutions containing the mediators, leukocyte migration and protein diffusion progressively decreased during the experiments. This suggests the local production of anti-inflammatory factors that inhibit local mediators and thus regulate the inflammatory response.