Increased levels of IL-5 positive peripheral blood eosinophils and lymphocytes in mild asthmatics after allergen inhalation provocation

Background In allergic inflammation eosinophils and TH2-Like lymphocytes ar e supposed to be the major effector cells and considered to contribute as c ellular source of the key cytokine interleukin (IL)-5. Objective The purpose of this study was to enable detection of IL-5 contain ing leucocytes and to investigate whether the number of these cells in the blood circulation differed between healthy and asthmatics before and after allergen provocation. Methods The distribution of intracellular IL-5 in human peripheral blood eo sinophils (PBE) and lymphocytes (PBL) has been investigated using fixation and cell membrane permeabilization with octyl-glucopyranoside, the FOG-meth od, and how cytometry. The intracellular staining was performed on leucocyt es without any prior purification and in vitro stimulation. The specificity of IL-5 binding to intracellular compartment of both PEE and PBL was confi rmed by complete inhibition with human recombinant IL-5. Results Preformed intracellular IL-5 was detected in the main population of PEE (> 70%) in both healthy individuals and asymptomatic patients. Moreove r, preformed intracellular IL-5 was also detected in 4.8% and 2.4% of PBL f rom healthy individuals and asymptomatic patients, respectively, There was a correlation between the absolute number of PEE and IL-5 positive PEE. In patients with pollen-related asthma, the number of IL-5 positive PEE and PB L increased significantly 24h after an allergen inhalation provocation (P<0 .05). In the healthy control group no differences regarding IL-5 positive P EE and PBL were obtained pre- and post-allergen challenge. Conclusions In patients with mild allergic asthma, but not in healthy indiv iduals, allergen provocation induces an increased absolute number of IL-5 p ositive PEE and PBL, The reason for the relatively high number of IL-5 posi tive PBL is unclear, but a plausible explanation might be that other lympho cyte subsets besides CD4(+) TH2 can produce IL-5. However, enumeration of I L-5 positive leucocytes may be used as an activity marker and also be a use ful tool in monitoring the inflammation in asthma.