Immune response in demodicosis

BACKGROUND: Demodex folliculorum and Demodex brevis are obligatory parasites in the hair follicles and in the pilosebaceous glands. Although most people are infested with these mites, only a small number develop the clinical symptoms of demodicosis. The objective of this study was to determine the distinguishing features of the immune response to the infestation of the skin by Demodex mites. METHODS: Twenty-nine patients with human demodicosis and 13 age- and sex-matched healthy subjects participated in the study. The presence of mites was determined by microscopic inspection of secretion from sebum glands. The immune response was evaluated in the peripheral blood by identifying membrane markers of different immune cells using monoclonal antibodies, while the concentration of immunoglobulin (Ig)A, IgM and IgG was calculated by simple radial immunodiffusion using anti-IgA, anti-IgM and anti-IgG. The level of circulating immune complexes and total haemolytic complement, as well as the preparatory and digestive function of neutrophils, and the functional activity of leucocytes were also studied. RESULTS: The absolute number of CD95+ was higher in patients with demodicosis. The absolute number of CD3+, CD4+, CD8+ and CD16+ cells, the ratio CD3+/CD20+ and the functional activity of leucocytes were significantly lower in individuals infested with Demodex mites. No significant differences were found in the percentage and absolute number of CD20+ cells, the ratio of CD4+/CD8+ T-cell subpopulations, circulating immune complexes, level of serum complement activity (CH(50)), activity and index of phagocytosis and the levels of IgA, IgM and IgG antibodies between individuals infested with Demodex mites and the control group. CONCLUSION: The readiness of lymphocytes to undergo apoptosis increases in parallel to the increasing density of the mites. This could be the result of local immunosuppression caused by the mites, which allows them to survive in the host skin.