CXCL12 and Langerhans cell histiocytosis: Based on our observations that intralesional blood vessels express CXCL12 and CXCL12-responsive CXCR4+ myeloid cells are circulating during active disease, we retrospectively investigated the clinical relevance of CXCR4 expression by lesional LCH-cells in relation to primary LCH manifestation and disease progression (Fig. 4A).