Project description:The discovery of hepatitis C virus (HCV) in 1989 revealed the virus as the etiology of 40%-90% of the “essential” mixed cryoglobulinemia, where immune complex forms deposit called cryoprecipitate at temperatures below 37 °C. Cryoprecipitate constitutes monoclonal IgM and polyclonal IgG, some of which has reactivity against HCV core and NS3 epitopes. Resultant immune complex is considered entrapped on microvascular endothelium via C1q receptor, leading to complement activation and organ injury presenting predominantly as dermopathy, peripheral neuropathy and nephropathy. However, currently little is known on whether auto-reactive, cold-precipitating IgG components enriched in cryoprecipitate may play some role on the deposition of immune complex and subsequent complement-mediated injury of specific organs. Recently, with the advent of high-throughput immune repertoire sequencing and mass spectrometry, technical feasibility is growing to delineate antibodies of interest and their sequences directly from serum. To date, vast majority of studies actually utilized the antigen column for affinity purification of antibodies of interest, although this strategy is not applicable to disease entity with unknown antigen involvement. In such cases, disease-specific and organ-specific immune deposits may be a good alternative source of etiological antibodies. Herein, targeting HCV cryoglobulinemic vasculitis as a model, we conducted a proof-of-concept study aiming at characterizing the IgG components most prone to cryoprecipitation. To this end, we longitudinally studied one patient with cryoglobulinemic vasculitis with chronic HCV infection. After obtaining informed consent, cryoprecipitate and supernatant were separated from peripheral blood sample. Fab fragments from Protein G-purified IgG were recovered after papain digestion for isobaric tags for relative and absolute quantification (iTRAQ)-based quantitative proteomics. Simultaneously, total RNA was isolated from peripheral blood, and immunoglobulin heavy chain variable region (IGHV) was PCR-amplified with unique molecular identifier (UMI) strategy to construct a personal IGHV sequence library of immunoglobulin variable region. Sequencing output from MiSeq was bioinformatically converted into mass spectrometry database. Search was performed using MaxQuant software.

Project description:Systemic lupus erythematosus is a chronic autoimmune disease with multifactorial ethiopathogenesis. The complement system is involved in both the early and late stages of disease development and organ damage. To better understand autoantibody mediated complement consumption the GAPAID consortium examined ex vivo immune complex formation on autoantigen arrays. We recruited patients with SLE (n=211), with other systemic autoimmune diseases (n=65) and non-autoimmune control subjects (n=149) in two rheumatology tertiary care centers. Standard clinical and laboratory data were collected from all subjects and serum complement levels were determined in SLE patients. The genotype of SNP rs1143679 in the ITGAM gene was also determined. On-chip formation of immune complexes was examined using a functional immunoassay on autoantigen microarray. The amount of antigen-bound IgM, IgG and complement C4 and C3 was quantified on autoantigens comprising nucleic acids, proteins and lipids. Our results show that the relatively high complement consumption of nucleic acids is further increased upon binding of IgM and IgG. This is true even when serum complement levels are decreased due to complement consumption in SLE patients. A negative correlation between serum complement levels and ex vivo complement deposition on nucleic acid autoantigens is demonstrated. On the contrary, most protein and lipid autoantigens show positive correlation with C4 and C3 levels. Genetic analysis reveals that the non-synonymous variant rs1143679 in complement receptor type 3 is associated with an increased production of anti-dsDNA IgG antibodies. Notwithstanding, homozygous carriers of the previously reported susceptible allele (AA) have lower levels of dsDNA specific IgM among SLE patients. Regarding organ involvement we find that besides anti-C1q IgG, low levels of dsDNA specific IgM and low complement C4 binding to C1q are also associated with renal injury. In summary, nucleic acids maintain a skewed complement deposition balance when bound by IgG and IgM, depleting the early classical complement pathway from other physiological processes. Dysfunction of the receptor responsible for complement-mediated apoptotic debris removal promotes the development of autoantibodies targeting nucleic acids. These observations provide serological and genetic evidence for complement-mediated clearance deficiency of apoptotic debris in lupus.

Dataset Information

HCV Cryoprecipitate LC-MS/MS with iTRAQ Quantification

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Delineation of autoantibody repertoire through differential proteogenomics in hepatitis C virus-induced cryoglobulinemia.

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