O’Neil et al. Allergy, Asthma & Clinical Immunology 2010, 6:28 http://www.aacijournal.com/content/6/1/28 Page 3 of 4 Figure 1 Immunostaining for osteopontin in nasal biopsies. Representative pictures of immunostaining for osteopontin in nasal biopsies of allergic rhinitis patients (peak-season, placebo treated) (×400) in epithelium (A) and glands (B). Arrows indicate OPN staining. While OPN is known to be produced by epithelial and endothelial cells in other healthy tissues [7], our data pro- vides the first example of the distribution in the nasal mucosa of AR patients. The expression of OPN protein in the nasal mucosa of healthy and AR subjects was predomi- nantly in the nucleus of the epithelial and endothelial cells (glandular and vesicular). Similarly, OPN expression has Figure 2 Percentage of osteopontin stained area in nasal biopsies pre- and peak season. The percentage of the osteopontin stained area in pre- and peak-season nasal biopsies of allergic rhinitis (AR) patients treated with placebo (P) or fluticasone propionate (FP). The mean and SEM is indicated per group. also been seen intracellularly in other nasal biopsies [12], as well as bronchial biopsies [10,11,16]. OPN has been seen to be expressed as a secreted form (s-OPN) and an intracellular form. The s-OPN is com- monly measured in different culture supernatants or body fluids. It is extensively modified post-translationally and acts like a Th1 cytokine. Intracellular OPN is less well characterised and has been reported as a transla- tional alternative to s-OPN. It has been shown to be involved in the modulation of cytoskeletal processes [17] as well as in the induction of IFN-a in plasmacytoid dendritic cells [18]. A previous study of the nasal biopsies reported here, looking at the expression of eosinophils [2], showed a clear increase in EG2+ cell numbers induced by a pollen season, which was inhibited with the use of FP. Eosino- phils have recently been discussed in relation to OPN [10,13] and as such, the correlation between OPN staining and EG2+ cell numbers was analysed. However, the increase in EG2+ cell numbers induced by season was not mirrored with an increase in OPN expression, confirming that eosinophils are not the only cells producing OPN. This study shows for the first time that the expression of OPN in the cells of the nasal mucosa of AR patients does not increase over a natural pollen season, although an increase in several cytokines and cells in the nasal mucosa over the pollen season has been reported [2,5,6]. The scope of this study is limited to the intracellular expression of OPN in the nasal mucosa of AR patients. It should be emphasised that although no differences in intracellular OPN expression were observed, this may not