However, it must be borne in mind that all these data were obtained in cell culture systems which only partially reflect the much more complex in vivo situation and that TLR9 inhibition did not show any significant effects on bone erosion or osteoclastogenesis (as estimated from the number of TRAP‐positive cells) in serum‐transfer arthritis or in established PIA. Here, CD40LG is linked to arthritic joint disease.