Incubation with either LPS or the pooled RASF containing high levels of endogenous TLR4 ligands, in contrast to non-RA SF (pooled from four subjects without RA), stimulated a significant increase in IL-6 release from RA-derived monocytes from seven individual RA donors (see Additional file 5) (data not shown). Here, TLR4 is linked to rheumatoid arthritis.