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Infections of the respiratory tract are very common in young children. They may affect the quality of life and have a great economic impact. On the other hand, respiratory tract infections through MALT system play a positive role in the maturation and development of the immune system. The aim of the study was to examine quantitative and qualitative changes of T and B cells and granulocytes surface molecules in 24 children with recurrent (more than 8 episodes per year) infections of the respiratory tract and in 18 healthy children. The expression of CD2, CD3, CD4, CD8 on T cells; HLA-DR, CD19, CD5/CD20 on B cells, and CD11a/CD18, CD11b/CD18, CD62L, CD16 on granulocytes from peripheral blood was evaluated by a flow cytometry method. We observed a significant increase in the CD5+/CD20+ positive cells on B cells. We also observed a decreased expression of CD11c+/CD18+ cells, CD11a, and CD62L on granulocytes. The expression of other structures on lymphocytes and the CD11b/CD18+ on granulocytes remained unchanged. CD5+/CD20+ cells constitute a filogenetically old population responsible for the production of IgM of low specificity and affinity for specific antigens. The prevalence of this fetal phenotype population may be explained as a delayed maturation of the humoral immune system leading to increased susceptibility to infections. A lower percentage of CD11a may be related to the blockade of that molecule by rhinoviruses.
Increased susceptibility to infections can be a consequence of altered function of immune cells including neutrophils. The goal of the study was to evaluate the process of neutrophil activation via Ca2+-mediated signal. The study was performed on isolated peripheral blood neutrophils obtained from 41 children with recurrent infections (21 girls, 20 boys) 3-10 years old with more than five episodes of respiratory tract infection (RI) per year and from a control group of 30 healthy children age and sex matched, free from allergic, immune and hematological disorders. Neutrophils were activated by bacterial peptide fMLP, opsonized zymosan (OZ), and phorbol myristat acetate (PMA). The kinetics of the intracellular Ca2+ concentration i[Ca2+] was assessed by flow cytometry (Coulter Epics XL) with the use of Fluo3 and Fura Red fluorescent dyes. Data were collected in histograms displaying Fluo3 fluorescence vs. time and Fura Red fluorescence vs. time and the mean channels of fluorescence intensity were used for calculations. fMLP and OZ-induced Ca2+ mobilization lasted shorter in the RI group (P<0.05). The peak influx of free Ca2+ and i[Ca2+] in the resting state after stimulation with fMLP were lower in the patients (P<0.05). In the RI group stimulation with OZ was delayed compared with that in the control group (P<0.01). In response to PMA, i[Ca2+] decreased faster. The kinetic slopes of i[Ca2+] in both groups examined differed statistically at all points measured. A decrease in i[Ca2+] after PMA stimulation was greater (P<0.01) and lasted longer in the RI group. We conclude that increased sensitivity to infections in RI children may be related to the disturbance in neutrophil activation that is mediated by changes in i[Ca2+] with the subsequent production of free oxygen radicals. Such a disturbance may be inheritable or secondary to infection and antibiotic therapy.
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