Histamine (0.004–2 μM) induced a concentration‐dependent shape change of human eosinophils, but not of neutrophils or basophils, detected as an increase in forward scatter (FSC) in the gated autofluorescence/forward scatter (GAFS) assay. The histamine‐induced eosinophil shape change was completely abolished by thioperamide (10 μM), an H3/H4 receptor antagonist, but was not inhibited by pyrilamine or cimetidine (10 μM), H1 and H2 receptor antagonists, respectively. The H4 receptor agonists, clobenpropit and clozapine (0.004–2 μM), which are also H3 receptor antagonists, both induced eosinophil shape change, which was inhibited by thioperamide (10 μM). The H3/H4 receptor agonists, imetit, R‐α‐methyl histamine and N‐α‐methyl histamine (0.004–2 μM) also induced eosinophil shape change. Histamine induced actin polymerisation (0.015–10 μM), intracellular calcium mobilisation (10–100 μM) and a significant upregulation of expression of the cell adhesion molecule CD11b (0.004–10 μM) in eosinophils, all of which were inhibited by thioperamide (10–100 μM). In addition, the H4 receptor agonist/H3 receptor antagonist clozapine (20 μM) stimulated a rise in intracellular calcium in eosinophils. Activation of H4 receptors by histamine (1 μM) primed eosinophils for increased chemotactic responses to eotaxin, but histamine (0.1–10 μM) did not directly induce chemotaxis of eosinophils. Pertussis toxin (1 μg ml−1) inhibited shape change and actin polymerisation responses induced by histamine showing that these effects are mediated by coupling to a Gαi/o G‐protein. This study demonstrates that human eosinophils express functional H4 receptors and may provide a novel target for allergic disease therapy. British Journal of Pharmacology (2003) 140, 1117–1127. doi:

Challenge of the airways of sensitized guinea pigs with aerosolized ovalbumin resulted in an early phase of microvascular protein leakage and a delayed phase of eosinophil accumulation in the airway lumen, as measured using bronchoalveolar lavage (BAL). Immunoreactive eotaxin levels rose in airway tissue and BAL fluid to a peak at 6 h falling to low levels by 12 h. Eosinophil numbers in the tissue correlated with eotaxin levels until 6 h but eosinophils persisted until the last measurement time point at 24 h. In contrast, few eosinophils appeared in BAL over the first 12 h, major trafficking through the airway epithelium occurring at 12–24 h when eotaxin levels were low. Constitutive eotaxin was present in BAL fluid. Both constitutive and allergen-induced eosinophil chemoattractant activity in BAL fluid was neutralized by an antibody to eotaxin. Allergen-induced eotaxin appeared to be mainly in airway epithelium and macrophages, as detected by immunostaining. Allergen challenge of the lung resulted in a rapid release of bone marrow eosinophils into the blood. An antibody to IL-5 suppressed bone marrow eosinophil release and lung eosinophilia, without affecting lung eotaxin levels. Thus, IL-5 and eotaxin appear to cooperate in mediating a rapid transfer of eosinophils from the bone marrow to the lung in response to allergen challenge.

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Mast cells are long-lived cells that are principally recognized for their effector function in helminth infections and allergic reactions. These cells are derived from pluripotential hematopoietic stem cells in the bone marrow that give rise to committed mast cell progenitors in the blood and are recruited to tissues, where they mature. Little is known about the chemotactic signals responsible for recruitment of progenitors and localization of mature mast cells. A mouse model was set up to identify possible mast cell progenitor chemoattractants produced during repeated allergen challenge in vivo. After the final challenge, the nasal mucosa was removed to produce conditioned medium, which was tested in chemotaxis assays against 2-wk murine bone marrow-derived c-kit ؉ mast cells (BMMC). A single peak of chemotactic activity was seen on reverse-phase HPLC with a retention time and electrospray mass spectrum consistent with prostaglandin E 2 (PGE2). This lipid was found to be a highly potent chemoattractant for immature (2-wk) and also mature (10-wk) BMMC in vitro. Fluorescently labeled 2-wk c-kit ؉ BMMC, when injected intravenously, accumulated in response to intradermally injected PGE2. Analysis using TaqMan showed mRNA expression of the PGE2 receptors 3 (EP3) and 4 (EP4) on 2-and 10-wk BMMC. Chemotaxis induced by PGE2 was mimicked by EP3 agonists, blocked by an EP3 receptor antagonist, and partially inhibited by a MAPKK inhibitor. These results show an unexpected function for PGE2 in the chemotaxis of mast cells.allergy ͉ eicosanoids ͉ migration