FOXP3 and autoimmune thrombocytopenic purpura: Clinical characteristics and decreased CD4&lt;sup&gt;+&lt;/sup&gt;CD25&lt;sup&gt;+&lt;/sup&gt;Foxp3&lt;sup&gt;+&lt;/sup&gt; regulatory T cells and IL-35 in pediatric immune thrombocytopenia in a single center.