Comparison of CD163 immunohistochemical stain of bone marrow one month before trial of anakinra trial (3a), and the day after discontinuation (3b). Shown at 40x magnification. CD163 is an immunohistochemical stain that is specific for monocytes and macrophages and the positive cells show brown surface staining. Prior to anakinra, there are slit-like macrophages and some with a few ingested cells (blue arrow). On repeat biopsy and stain done after anakinra, there is an increase in the number of macrophages and the CD163 stain demonstrates numerous hemophagocytic macrophages containing multiple ingested cells (blue arrows).