Immunochemical Characterization of the Anti-RNA Antibodies Found in Scleroderma and Systemic Lupus Erythematosus

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Abstract
In a previous study, all 40 sera from patients with scleroderma, 20 of 40 sera from SLE patients, but none of 40 sera from normal controls, were found to have antibodies to ssRNA. All scleroderma sera were also found to react with HSA-coupled uridine and UMP and their reaction with ssRNA could be inhibited by uracil, uridine, and UMP. To characterize further these uracil-specific anti-RNA antibodies found in scleroderma and compare them with the anti-RNA antibodies found in SLE, we tested their reactivity with Poly (U) and with Poly (A)·Poly(U) in CIE. All 40 scleroderma sera reacted with Poly (U) and all but one failed to react with Poly (A)·Poly(U). This same serum was the only one in which the reaction with Poly (U) could not be inhibited with uracil. Reactivity of SLE sera was strikingly different from that found in scleroderma sera. Seventeen of 34 SLE sera studied reacted with ssRNA but only four of these reacted with Poly (U). Conversely, two SLE sera that reacted with Poly (U) did not react with ssRNA. Fifteen reacted with Poly (A)·Poly (U) and only two of these failed to react with ssRNA. Five SLE sera which were reactive with ssRNA did not precipitate with Poly (A)·Poly (U). All SLE sera which reacted with Poly (U) could be inhibited with uracil, although less effectively than in scleroderma. Reactivity with Poly (A)·Poly (U) was not inhibited with uracil nor with adenosine. These findings confirm that antibodies to RNA that are found in scleroderma are directed to uracil and thus specific to ssRNA, whereas RNA antibodies found in SLE sera are heterogeneous and directed to either the base, to the site of union of the base and sugar moiety to the ribose backbone, or to the helical structure of double stranded RNA. These differences and the respective antigenic specificities of these anti-RNA antibodies found in scleroderma and SLE may be theoretically important.

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