The Journal of Immunology, Vol 156, Issue 4 1668-1675, Copyright © 1996 by American Association of Immunologists

ARTICLES

Lupus autoantibodies to double-stranded DNA cross-react with ribosomal protein S1

K Tsuzaka, AK Leu, MB Frank, BF Movafagh, M Koscec, TH Winkler, JR Kalden and M Reichlin
Arthritis and Immunology Program, Oklahoma Medical Research Foundation, Oklahoma City 73104, USA.

One cDNA clone (G7) was isolated from a lambda gt11 human liver cDNA library by the reaction with a serum containing anti-dsDNA Abs and was ligated into pGEX-1 lambda T vector. All the 10 SLE sera with anti- dsDNA, 2 samples of human monoclonal anti-dsDNA (33.C9 and 33.H11), and 2 affinity-purified anti-dsDNA Abs recognized the glutathione S- transferase fusion protein expressed by G7 (G7-FP). Ab binding to the recombinant protein expressed by G7 (G7-RP) and to G7-FP was inhibited completely by calf thymus dsDNA. The cDNA was 1314 nucleotides in length and contained an open reading frame encoding 352 amino acids. However, it seems to be a partial length cDNA because the affinity- purified Ab from G7-FP recognized only a 104-kDa protein on Western blot using MOLT4 cell extract. The nucleotide sequence of G7 was homologous (99% identity) to a cDNA encoding human ribosomal protein (r- protein) S1 homologue mRNA. The encoded protein contains repeating residues as a feature of r-proteins S1. Cytoplasmic and nucleolar staining of 33.H11 on indirect immunofluorescence (IF) using HEP 2 cells was inhibited by both G7-RP and calf thymus dsDNA. On ELISA, 33.H11 had a higher affinity for G7-RP than for DNA while 33.C9 had a higher affinity for DNA than for G7-RP and binds nuclei on IF. We conclude that G7 encodes a portion of human r-protein S1 and anti-dsDNA Abs cross-react with this protein.

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