CD1A and Langerhans cell histiocytosis: In addition, LCH CD1a+ cells, which are presumed to be pathologic, very slowly proliferate in most patients [12], while the expansion of a monocyte or dendritic cell compartment, which represent candidate precursors for these CD1a+ cells of the granuloma, was not consistently observed in the blood of LCH patients [12], [27].