Genome-wide association study of hepatitis C virus- and cryoglobulin-related vasculitis

The host genetic basis of mixed cryoglobulin vasculitis is not well understood and has not been studied in large cohorts. A genome-wide association study was conducted among 356 hepatitis C virus (HCV) RNA-positive individuals with cryoglobulin-related vasculitis and 447 ethnically matched, HCV RNA-positive controls. All cases had both serum cryoglobulins and a vasculitis syndrome. A total of 899 641 markers from the Illumina HumanOmni1-Quad chip were analyzed using logistic regression adjusted for sex, as well as genetically determined ancestry. Replication of select single-nucleotide polymorphisms (SNPs) was conducted using 91 cases and 180 controls, adjusting for sex and country of origin. The most significant associations were identified on chromosome 6 near the NOTCH4 and MHC class II genes. A genome-wide significant association was detected on chromosome 6 at SNP rs9461776 (odds ratio=2.16, P=1.16E-07) between HLA-DRB1 and DQA1: this association was further replicated in additional independent samples (meta-analysis P=7.1 × 10(-9)). A genome-wide significant association with cryoglobulin-related vasculitis was identified with SNPs near NOTCH4 and MHC Class II genes. The two regions are correlated and it is difficult to disentangle which gene is responsible for the association with mixed cryoglobulinemia vasculitis in this extended major histocompatibility complex region

Primary, post-primary and non-specific immunoglobulin M responses in HCV infection

Delayed and variable antibody responses to HCV make it difficult to diagnose acute HCV infection reliably. Immunoglobulin (Ig)M and IgG anti-HCV may be observed simultaneously as disease persists. IgM plays a key role in mixed cryoglobulinemia (MC), an immune complex disease strongly associated with persistent HCV infection. In MC, clonal or oligoclonal IgM rheumatoid factors facilitate the deposition of immune complexes in small blood vessels and tissue, leading to inflammation, complement activation and tissue damage. Clonally expanded IgM(+)κ(+) B-cells expressing rheumatoid factor-like IgM are abundant in many HCV patients with MC. The observation that identical or similar IgM antibodies are expressed in different patients' clonally expanded B-cells supports the hypothesis that MC is driven by antigen-specific B-cell activation, rather than polyclonal B-cell activation or HCV replication in B-cells. More study is required to identify the antigens that drive the development of MC

A flow cytometry-based strategy to identify and express IgM from VH1-69+ clonal peripheral B cells.

Pathologic rheumatoid factor (RF) levels are hallmarks of several human diseases. Production of monoclonal RF in vitro is essential for studies of the antigenic specificities of RF, as well as for a dissection of the mechanisms of aberrant RF+ B cell activation. We have expanded upon previous methods to develop a flow cytometry-based method to efficiently clone monoclonal antibodies (mAbs) from humans with expansions of RF-like, immunoglobulin heavy chain variable region (IgVH) 1-69 gene segment-containing B cells. The cloned variable regions are expressed as IgM and produced during culture at concentrations between 5 and 20 μg/ml. Using this system, we show that clonal Igs from patients with HCV-related mixed cryoglobulinemia, when expressed as IgM, have RF activity. We anticipate that this system will be useful for the cloning and expression of mAbs partially encoded by VH1-69 and for determination of the reactivity patterns of polyspecific, low-affinity IgMs of human pathogenic importance

Cell culture-produced hepatitis C virus does not infect peripheral blood mononuclear cells.

Hepatitis C virus (HCV) replicates primarily in the liver, but HCV RNA has been observed in association with other tissues and cells including B and T lymphocytes, monocytes, and dendritic cells. We have taken advantage of a recently described, robust system that fully recapitulates HCV entry, replication and virus production in vitro to re-examine the issue of HCV infection of blood cell subsets. The HCV replicase inhibitor 2'C-methyl adenosine was used to distinguish HCV RNA replication from RNA persistence. Whereas cell culture-grown HCV replicated in Huh-7.5 hepatoma cells, no HCV replication was detected in B or T lymphocytes, monocytes, macrophages, or dendritic cells from healthy donors. No blood cell subset tested expressed significant levels of Claudin-1, a tight junction protein needed for HCV infection of Huh-7.5 cells. A B cell line expressing high levels of Claudin-1, CD81, and scavenger receptor BI remained resistant to HCV pseudoparticle infection. We bypassed the block in HCV entry by transfecting HCV RNA into blood cell subsets. Transfected RNA was not detectably translated and induced high levels of interferon-alpha. Supernatants from HCV RNA-transfected macrophages inhibited HCV replication in Huh-7.5 cells.We conclude that multiple blocks prevent blood cells from supporting HCV infection