Increased number of CD34 1 cells in nasal mucosa of allergic rhinitis patients: inhibition by a local corticosteroid S. Sergejeva, C. Malmha¨ll, J. Lo¨tvall and T. Pullerits The Lung Pharmacology Group, Department of Respiratory Medicine and Allergology, Institute of Internal Medicine, Go ¨teborg University, Gothenburg, Sweden Summary Background Eosinophils develop from CD34 1 haematopoietic progenitor cells. Allergen exposure in susceptible individuals is known to induce a local eosinophilic inflammation, but the effect on progenitor cells is much less understood. Objective We aimed to evaluate how allergen exposure affects the number of tissue CD34 1 cells and CD34 1 eosinophils in allergic rhinitis (AR) patients and whether any such effect is influenced by local corticosteroid treatment. Also, we evaluated changes in the number of CXC receptor 4-positive cells (CXCR4 1 ), since the CXCR4 ligand (stromal cell-derived factor-1 (SDF-1)) is a potent chemoattractant for haematopoietic progenitors. Methods In a double-blind, randomized study, pollen-sensitized AR patients were treated with a nasal corticosteroid fluticasone propionate (FP, 200 mg/day) or placebo throughout the pollen season. Nasal biopsies were taken before and during the season. CD34 and CXCR4 were stained using immunohistochemistry. Results The pollen season significantly increased the number of CD34 1 cells, CD34 1 /CXCR4 1 cells and CD34 1 eosinophils in placebo-treated patients, but not in FP-treated patients. The mean pollen season-induced increase in CD34 1 cells, CD34 1 /CXCR4 1 cells and CD34 1 eosinophils in FP-treated patients was lower compared with placebo-treated patients. Conclusion A pollen season increases the number of CD34 1 cells in nasal tissue accompanied by an increase in the number of CD34 1 /CXCR4 1 haematopoietic progenitors and also the number of CD34 1 eosinophils in subjects with AR. Treatment with a local corticosteroid provides protection against this pollen-induced increase in tissue CD34 1 cells and CD34 1 eosinophils possibly via inhibition of allergen-induced CXCR4-mediated recruitment of CD34 1 haematopoietic progenitors into airways and their further differentiation into eosinophils within the tissue. Keywords allergic rhinitis, CD34 1 cells, haematopoietic progenitor, local corticosteroid Submitted 12 August 2003; revised 17 May 2004; accepted 27 May 2004 Introduction Local airway inflammation in allergic rhinitis (AR) is characterized by the infiltration of mucosa with eosinophils. Products from eosinophils such as platelet-activating factor, leukotrienes and eosinophil granule proteins may account for the prolonged nasal congestion and mucus secretion observed during natural allergen exposure in grass-pollen season. Increased number of airway eosinophils is the result of increased eosinophil differentiation within bone marrow and their recruitment via the circulation into airways [1–3]. Eosinophils develop from the CD34 antigen bearing haema- topoietic progenitor cells, which is stage-specific rather than lineage-specific leucocyte differentiation antigen. Its expres- sion appears at the highest density on earlier progenitors, decreases progressively with cell maturation and is lost on terminally differentiated cells. Apart from increased eosino- phil number, atopic subjects have increased number of CD34 1 cells in bone marrow, blood [3] and airways [4]. Importantly, airway CD34 1 cells differentiate into eosino- phils following ex vivo stimulation with allergen [5]. These data suggest that eosinophil differentiation may also occur within the airways. To date, there are no data available regarding allergen-induced changes in tissue progenitor cells in airways of atopic patients. Furthermore, it is not clear whether tissue CD34 1 cells are airway residing cells or are recruited into airways in response to allergen exposure. Local corticosteroids are used as anti-inflammatory treat- ment in allergic airway diseases. They are known to diminish the number of airway eosinophils as well as progenitor cells in blood and bone marrow of atopic asthmatics [6, 7]. To date, only one study has evaluated the effect of a local corticoster- oid on airway progenitor cells, demonstrating an increase in the expression of CD34 antigen in nasal polyp tissue follow- ing corticosteroid treatment [8]. However, the effect of a local Correspondence: Teet Pullerits, The Lung Pharmacology Group, Depart- ment of Respiratory Medicine and Allergology, Institute of Internal Medicine, Go¨teborg University, Guldhedsgatan 10A, 413 46 Gothenburg, Sweden. E-mail: teet.pullerits@lungall.gu.se Clin Exp Allergy 2005; 35:34–38 doi:10.1111/j.1365-2222.2004.02038.x r 2004 Blackwell Publishing Ltd 34