CD68 and osteoarthritis, knee: Also, although identification of the potential source(s) responsible for modulating serum IL-10 is beyond the scope of the present investigation, it is plausible that a lower anti-inflammatory cytokine concentration with severe or end-stage knee osteoarthritis—when the majority of the cartilage damage has already occurred—associates with an alteration in the number of infiltrating mononuclear cells (e.g., CD4 + and CD68 + cells)28,52–56, chondrocytes27,57, and other sources that contribute to its production.