Searching for a placental derived ES-62-like molecule to explain rheumatoid arthritis amelioration in pregnancy

The majority of women with rheumatoid arthritis (RA) experience disease amelioration during pregnancy for unclear reasons. One possible explanation pursued and described here is whether the placenta produces a protein similar to the immunomodulating protein, ES-62, excreted by filarial nematodes. This protein has also been shown to reduce disease activity in animal models of RA. Eleven human placentas were prepared and a polyclonal anti-ES-62 antiserum was used to identify if any ES-62-like molecule exists from human placental tissues. Any bands identified were then excised from the gel and sent for mass spectrometry and protein identification. The anti-serum showed consistent cross reactivity with the heavy chain from immunoglobulin G (IgG) from the eleven human placentas by mass spectrometry. No primary sequence homology between the heavy chain of IgG and ES-62 was identified. The placenta does not produce an ES-62-like molecule. However the binding of the antiserum to the Fc region of IgG suggests that this may be a possible mechanism for rheumatoid factor production in some patients with chronic filarial infections.