Our finding of a statistically significant correlation of sP-selectin levels with IgM and IgG antibodies against HpmB in the subgroup of RA patients without treatment suggests that the antibodies against P. mirabilis through molecular mimicry and cross-reaction mechanisms with tissue antigens of the joints provoke an increased expression of sP-selectin, which contributes to the inflammation of the joints and the activation of RA. This evidence concerns the gene CD40LG and rheumatoid arthritis.