A. During an inflammatory HSP flare, is there a quantitative and / or qualitative defect in plasma Tregs? Are such blood anomalies real or are they due to a modification of the distribution of theses cells to localized sites? B. In the asymptomatic phase, are there quantitative or functional abnormalities among Tregs in subjects with HSP compared to healthy control subjects? C. Are Treg abnormalities associated with modifications in other blood cell lineages, including B cells secreting IgA and abnormally glycosylated IgA1, and secretion of cytokines during acute relapses and during the asymptomatic phase? D. Can streptococcus or other oral or digestive pathogens (bacterial or viral) (as suggested in other chronic diseases such as rheumatoid arthritis ) provoke (via stimulation Th3) isotype commutation towards secretion of IgA1 at the origin of HSP? Does HSP intestinal damage or imbalance of the intestinal microbiota allow the translocation of intestinal microorganisms that sustain this stimulation?