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Keywords:

  • alpha-macroglobulins;
  • anti-IgE;
  • atopy;
  • eosinophils;
  • histamine;
  • loratadine;
  • mast cells;
  • skin

The aim of this study was to assess the ability of the H1-receptor antagonist loratadine to modify anti-IgE-induced cutaneous wheal-and-flare and late-phase reactions (WFR and LPR), as well as histamine release and leukocyte accumulation in skin chambers. For this purpose, 10 atopics with allergic rhinitis were entered into a double-blind crossover study in which they received either placebo or loratadine (20 mg/day orally) for 8 days separated by a 7-day washout period. Blisters were induced on both forearms on day 7 of each treatment period, and were unroofed on day 8 and covered with plastic skin chambers. Chamber fluids were collected during 7 h after 1-h incubation with anti-IgE or control IgG. Intradermal challenge with histamine and anti-IgE was performed at the same occasion. As compared to placebo treatment, loratadine inhibited the immediate WFRs to anti-IgE by 35% (wheal) and 65% (flare), respectively (P < 0.01), and corresponding reactions to histamine challenge by 50% and 70% (P<0.001), respectively. Moreover, the initial phase (0-2 h) of the LPR induced by anti-IgE was attenuated by up to ∼60% (P < 0.001) during loratadine treatment. Thereafter, no inhibition of the LPR was observed. The magnitude and time course of histamine release into skin chambers was virtually the same after loratadine and placebo treatment, with a peak during 0-1 h and a progressive decline during the following 2 h. Accumulation of α2-macroglobulin, reflecting extravasation of large plasma proteins, also peaked during the first hour and was unaffected by loratadine during the 8-h observation period. Moreover, loratadine did not reduce the anti-IgE-induced recruitment of eosinophils or other subtypes of leukocytes. Altogether, loratadine inhibited both the WFRs to histamine and anti-IgE and the initial phase of the IgE-mediated LPR. However, loratadine did not express anti-inflammatory activity with respect to mast-cell mediator release or leukocyte recruitment. The latter findings are in contrast to the action of loratadine in allergic rhinitis and conjunctivitis, suggesting that the actions of loratadine may be organ specific and that the effects of loratadine cannot always be extrapolated from one tissue to another.