Text Box: EFFECT OF LEUKOTRIENE RECEPTOR INHIBITOR IN CLINICAL ASTHMA, PERIPHERAL BLOOD EOSINOPHIL COUNTS, SERUM IgE LEVELS AND CD11b, CD11c, CD23 EXPRESSION IN ASTHMATIC CHILDREN Aberle N, Gagro A*, Rabatic S*, Dekaris D*, Bublic J. General Hospital “Dr. Josip Bencevic” Slavonski Brod, *Institute of Immunology, Zagreb, Croatia The cysteinyl leukotrienes are potent proinflammatory mediators that contribute to pathophysiologic features observed in allergic asthma. The cysteinyl leukotrienes LTC4, LTD4 and LTE4 are known bronchoconstrictiors, induces of airway microvascular leakage and oedema, and of mucus secretion, in addition to cousing an eosinophilic airway infiltration. Inhibitors of leukotrienes receptors (Montelukast) represent novel therapy in asthma treatment. Montelukast (Singulaire) is a potent, selective, orally active leukotriene receptor antagonist, which protect both, early and late asthmatic responses. We have studied the effect of treatment with oral inhibitor of leukotriene receptor on the increased expression of low affinity IgE receptor, CD23, and its ligand, CD11b and CD11c on peripheral blood lymphocytes asthma symptom score, peripheral blood eosinophil counts, and serum IgE levels in patients with allergic asthma. Twelve children with allergic asthma (8 boys, 4 girls; age median value 11.5 years) received montelukast, a leukotriene receptor inhibitor after demonstrating forced expiratory volume in 1 second (FEV1) of less than 80% of the predicted value for a period of 6-8 weeks. Samples of peripheral heparinized blood and serum were taken before and after the completion of the therapy. Three-color immunofluorescence analysis was performed and expression of CD11b and CD11c on CD4+ T lymphocytes as well as the expression of CD21 and CD23 on B lymphocytes were determined. Peripheral blood eosinophil counts, changes in FEV1 and peak expiratory flow rate (PEFR), asthma exarcerbations and “as needed” beta-agonist use were also monitored. We have observed that montelukast improved FEV1 and PEFR and decreased peripheral blood eosinophil counts and serum IgE levels. This was not accompanied with significant changes in the expression of CD23, CD11b and CD11c. We conclude that in contrast to hyposenzibilization, inhibitors of leukotriene receptors might need more prolonged treatment to exert its potential effect on cells which are important participants of allergic response such as CD11b+ T and CD23+ B lymphocytes. 2012