CD40LG and systemic lupus erythematosus: Interestingly, it has been reported that anti-PC IgM antibodies can counteract IL-6 upregulation in vitro and in vivo22, probably by the inhibition of MAPK responses to TLR agonists, including lupus immune complexes50, thus explaining the opposite associations of these natural antibodies with Synergistetes and IL-6.