C‑reactive protein isoforms help to differentiate between SLE quiescent and active phenotypes

A recent study published in the Arthritis Research & Therapy has reported that the interrelationship between the pentameric CRP (pCRP) and monomeric isoforms (mCRP) helps to differentiate between quiescent and active SLE. These 2 isoforms demonstrate contradictory immunological effects and/or diverse milieus and also assist in differentiating SLE and antibody-associated vasculitis.

SLE is an autoimmune disease marked by increased production of autoantibodies and limited cellular waste clearance. These autoantibodies along with soluble antigens constitute immune complexes, which in turn accumulate in tissues, recruit complement, resulting in inflammation and tissue damage. The pCRP isoforms generally indicate underlying inflammation and tissue damage, whereas, the mCRP), which mainly has been correlated with the pro-inflammatory properties. The deranged levels of mCRP may be suggestive of elevated opsonization of immune complexes and apoptotic debris, thereby preventing their deposition exterior to reticuloendothelial system and the associated manifestations such as skin lupus and lupus nephritis.

The researchers measured the levels of both isoforms using turbidimetry (high-sensitive) and sandwich enzyme linked immunosorbent assay (ELISA) in serum samples obtained from 160 SLE patients and 30 patients with antibody-associated vasculitis (AAV). The two CRP isoforms were evaluated with regard to the disease activity and clinical features of the 2 diseases.

Levels of both the isoforms were found to be substantially lower in SLE than patients with AAV (p < 0.001) and the ratio of mCRP to pCRP was found to be elevated in SLE patients as opposed to those with AAV. The ratio was also found to be higher in patients on remission, which helped to differentiate between active and quiescent SLE. Significant associations were noted for pCRP levels with SLICC/ACR damage index and inversely with the mCRP/pCRP ratio. Malar rash was found in patients with reduced mCRP levels.

The present study is first-of-its-kind evaluating the two isoforms of CRP in SLE. Further evaluation of this associations of C‑reactive protein isoforms with SLE phenotypes could be beneficial in developing novel diagnostic and therapeutic modalities.

Reference: Karlsson J, Wetterö J, Weiner M, Rönnelid J, Fernandez-Botran R, Sjöwall C. Associations of C-reactive protein isoforms with systemic lupus erythematosus phenotypes and disease activity. Arthritis Res Ther. 2022;24(1):139.