"Endogenous adjuvant" activity of the RNA components of lupus autoantigens Sm/RNP and Ro 60

Arthritis Rheum. 2006 May;54(5):1557-67. doi: 10.1002/art.21819.

Abstract

Objective: Most lupus patients produce autoantibodies against small ribonucleoproteins such as Sm/RNP and Ro 60 (containing U1 and Y1-Y5 RNAs, respectively). We undertook this study to investigate whether the RNA components of these antigens, which contain extensive tracts of single- and double-stranded RNA, signatures of viral infection, activate innate immunity.

Methods: U1 and Y RNAs were affinity purified from K562 cells. Murine bone marrow-derived dendritic cells (DCs), human HEK 293 cells, and murine RAW264.7 cells were stimulated with U1 RNA and other known Toll-like receptor (TLR) ligands. Expression of the interferon (IFN)-inducible gene Mx1 and other genes was quantified using real-time polymerase chain reaction, and cytokine production was measured by enzyme-linked immunosorbent assay. DC maturation was assessed using flow cytometry.

Results: Purified U1 and Y1-Y5 RNAs and synthetic stem-loop II of U1 RNA stimulated type I IFN (IFN-I) production by cell lines and murine bone marrow-derived DCs and promoted DC maturation (CD86 expression). U1 RNA-stimulated, but not TLR-3 ligand-stimulated, IFN-I was blocked by bafilomycin A1, indicating that immunostimulation by U1 RNA requires endosomal acidification. Myeloid differentiation factor 88-deficient cells responded poorly to U1 RNA, suggesting that an endosomal TLR, probably TLR-7, mediates the stimulatory effects of U1 RNA. U1 RNA-induced IFN-I and interleukin-6 production also were protein kinase R (PKR) dependent (abrogated by 2-aminopurine and greatly reduced in PKR-/- cells).

Conclusion: We conclude that the RNA components of the Ro 60 (Y1-Y5 RNA) and Sm/RNP (U1 RNA) small ribonucleoproteins act as endogenous adjuvants that could play a role in the pathogenesis of autoimmunity by stimulating DC maturation and IFN-I production.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Autoantigens / immunology*
  • Cells, Cultured
  • Endosomes / immunology
  • Humans
  • Interferon Type I / biosynthesis
  • Lupus Erythematosus, Systemic / immunology*
  • Mice
  • RNA, Small Cytoplasmic / immunology*
  • Ribonucleoproteins / immunology*
  • Ribonucleoproteins, Small Nuclear / immunology*
  • Toll-Like Receptors / physiology

Substances

  • Autoantigens
  • Interferon Type I
  • RNA, Small Cytoplasmic
  • RO60 protein, human
  • Ribonucleoproteins
  • Ribonucleoproteins, Small Nuclear
  • Toll-Like Receptors