Coxsackievirus B3 infection induces anti-flavoprotein antibodies in mice

A comprehensive autoantigen-ome of autoimmune liver diseases identified from dermatan sulfate affinity enrichment of liver tissue proteins

BACKGROUND

Autoimmune diseases result from aberrant immune attacks by the body itself. It is mysterious how autoantigens, a large cohort of seemingly unconnected molecules expressed in different parts of the body, can induce similar autoimmune responses. We have previously found that dermatan sulfate (DS) can form complexes with molecules of apoptotic cells and stimulate autoreactive CD5+ B cells to produce autoantibodies. Hence, autoantigenic molecules share a unique biochemical property in their affinity to DS. This study sought to further test this uniform principle of autoantigenicity.

RESULTS

Proteomes were extracted from freshly collected mouse livers. They were loaded onto columns packed with DS-Sepharose resins. Proteins were eluted with step gradients of increasing salt strength. Proteins that bound to DS with weak, moderate, or strong affinity were eluted with 0.4, 0.6, and 1.0 M NaCl, respectively. After desalting, trypsin digestion, and gel electrophoresis, proteins were sequenced by mass spectrometry. To validate whether these proteins have been previously identified as autoantigens, an extensive literature search was conducted using the protein name or its alternative names as keywords. Of the 41 proteins identified from the strong DS-affinity fraction, 33 (80%) were verified autoantigens. Of the 46 proteins with moderate DS-affinity, 27 (59%) were verified autoantigens. Of the 125 proteins with weak DS-affinity, 44 (35%) were known autoantigens. Strikingly, these autoantigens fell into the classical autoantibody categories of autoimmune liver diseases: ANA (anti-nuclear autoantibodies), SMA (anti-smooth muscle autoantibodies), AMA (anti-mitochondrial autoantibodies), and LKM (liver-kidney microsomal autoantigens).

CONCLUSIONS

This study of DS-affinity enrichment of liver proteins establishes a comprehensive autoantigen-ome for autoimmune liver diseases, yielding 104 verified and 108 potential autoantigens. The liver autoantigen-ome sheds light on the molecular origins of autoimmune liver diseases and further supports the notion of a unifying biochemical principle of autoantigenicity.

Specific stimulation of peripheral blood mononuclear cells from patients with acute myocarditis by peptide-bound flavin adenine dinucleotide (FAD), a naturally occurring autologous hapten

The tryptic FAD-peptide carrying the flavin in 8alpha-(N3)histidyl linkage as natural hapten was isolated by HPLC from the bacterial enzyme 6-hydroxy-d-nicotine oxidase. The same flavin protein linkage is found in the mitochondrial succinate dehydrogenase flavoprotein subunit, the predominant flavoprotein with covalently bound FAD in mitochondria of cardiomyocytes. Peripheral blood mononuclear cells (PBMC) were isolated from four patients with acute myocarditis, seven patients with dilated cardiomyopathy (DCM) and from four healthy control individuals. The response of PBMC to the FAD-peptide was evaluated by measuring proliferation ([3H]-dThd incorporation) and cytokine secretion [interferon (IFN)-gamma]. PBMC from all patients with acute myocarditis showed positive responses to the FAD-peptide, in contrast to PBMC from patients with DCM or control individuals. Following the recovery of the patients from the acute inflammation of the heart, PBMC no longer exhibited a proliferation response to the FAD-peptide. A chemically synthesized FAD-free peptide with identical amino acid sequence induced no response of PBMC. The results are consistent with a recall response by activated T cells, specific for the normally cryptic mitochondrial flavin-hapten, which may be liberated following cardiomyocyte destruction during the inflammation of the heart.