Edward J. Ball

HLA-B27 and genetic predisposing factors in spondyloarthropathies.

With the mapping of the human genome having been completed, our ability to investigate and ideally better understand the genetic basis of rheumatic diseases is advancing at a rapid pace. Substantial evidence strongly favors a direct role for HLA-B27 in genetic susceptibility to ankylosing spondylitis and related spondyloarthropathies, although the underlying molecular basis has yet to be identified. HLA-B27 contributes only 16 to 50% of the total genetic risk for the disease, clearly indicating that other genes must be involved. However, no other putative disease genes have yet been absolutely proven. Potential genes include MHC (HLA class II, low molecular weight proteasome [LMP], transporter associated with antigen processing (TAP), tumor necrosis factor [TNF]-&agr;, and major histocompatibility complex class I chain-related gene A (MICA), as well as non-MHC genes (IL-1RA, IL-6, IL-10, and CYP2D6). Genome-wide screens have identified other chromosomal areas of interest: 1p, 2q, 6p, 9q, 10q, 16q, and 19q. However, different studies have given conflicting results. HLA-B27 itself is a serologic specificity, which encompasses 25 different alleles that encode 23 different products (proteins): HLA-B*2701 to B*2723. These alleles may have evolved from the most widespread subtype, B*2705, and two of them, B*2706 in Southeast Asia and B*2709 in Sardinia, seem not to be associated with ankylosing spondylitis. The distinction between the disease associated and nonassociated subtypes may provide clues to the actual role of B27 in disease pathogenesis.

Increased Frequencies of Cochlin-Specific T Cells in Patients with Autoimmune Sensorineural Hearing Loss

Autoimmune sensorineural hearing loss (ASNHL) is the most common cause of sudden hearing loss in adults. Although autoimmune etiopathogenic events have long been suspected in ASNHL, inner ear-specific Ags capable of targeting T cell autoreactivity have not been identified in ASNHL. In this study, we show by ELISPOT analysis that compared with normal hearing age- and sex-matched control subjects, ASNHL patients have significantly higher frequencies of circulating T cells producing either IFN-γ (p = 0.0001) or IL-5 (p = 0.03) in response to recombinant human cochlin, the most abundant inner ear protein. In some patients, cochlin responsiveness involved both CD4+ and CD8+ T cells whereas other patients showed cochlin responsiveness confined to CD8+ T cells. ASNHL patients also showed significantly elevated cochlin-specific serum Ab titers compared with both normal hearing age- and sex-matched control subjects and patients with noise- and/or age-related hearing loss (p < 0.05 at all dilutions tested through 1/2048). Our study is the first to show T cell responsiveness to an inner ear-specific protein in ASNHL patients, and implicates cochlin as a prominent target Ag for mediating autoimmune inner ear inflammation and hearing loss.

HLA-B27 polymorphism.

HLA-B27 is a serologic specificity that encompasses 25 different alleles that encode 23 different products (proteins): HLA-B*2701 to B*2723. These alleles are also called subtypes of HLA-B27, and they may have evolved from the most widespread subtype, B*2705. These subtypes are distinguished from changes mostly in exons 2 and 3, which encode the alpha 1 and alpha 2 domains of the B27 molecule, respectively. Occurrence of ankylosing spondylitis (AS) or related spondyloarthropathy (SpA) has thus far been documented in subjects possessing any one of the first ten (B*2701 to B*2710) subtypes studied. However, B*2706 in Southeast Asian and B*2709 in the Italian island population of Sardinia seem not to be associated with AS. The 13 most recent subtypes have not yet been studied for disease association. It is important to investigate which of them are and are not associated with AS and related SpA, and whether certain subtypes show any preferential association with some of the clinical features or forms of these diseases among the various ethnic/racial populations and geographic regions of the world. This is expected to provide clues as to the mechanism of disease association, and one of the strongest reasons to study the B27 subtypes is to learn the effects of the sequence variations on the peptide-binding specificity of the molecule. Among these peptides may be the putative arthritogenic peptide(s).

Immunogenetic factors determining the evolution of T-cell large granular lymphocyte leukaemia and associated cytopenias

T‐cell large granular lymphocyte leukaemia (T‐LGL) is a chronic clonal proliferation of cytotoxic T lymphocytes (CTL). T‐LGL presents with cytopenias, often accompanied by autoimmune diseases, suggesting clonal transformation arising from an initially polyclonal immune response. Various immunogenetic predisposition factors, previously described for both immune‐mediated bone marrow failure and autoimmune conditions, may promote T‐LGL evolution and/or development of cytopenias. The association of T‐LGL was analysed with a number of immunogenetic factors in 66 patients, including human leucocyte antigen (HLA) and killer‐cell immunoglobulin‐like receptor (KIR) genotype, KIR/KIR‐L mismatch, CTLA‐4 (+49 A/G),CD16−158V/F, CD45 polymorphisms, cytokine single nucleotide polymorphisms including: TNF‐α (−308G/A), TGF‐β1 (codons 10 C/T, 25 G/C), IL‐10 (−1082 G/A), IL‐6 (−174 C/G), and IFN‐γ(+874 T/A). A statistically significant increase in A/A genotype for TNF‐α−308, IL‐10–1082, andCTLA‐4 +49 was observed in T‐LGL patients compared with control, suggesting that the G allele serves a protective role in each case. No association was found between specific KIR/HLA profile and disease. KIR/KIR‐L analysis revealed significant mismatches between KIR3DL2 and KIR2DS1 and their ligands HLA‐A3/11 and HLA‐C group 2 (P = 0·03 and 0·01 respectively); the biological relevance of this finding is questionable. The significance of additional genetic polymorphisms and their clinical correlation to evolution of T‐LGL requires future analysis.

HLA-DRB1* Intron-primed Sequencing for Haploid Genotyping

The HLA genes of the MHC on chromosome 6p manifest extensive allelic polymorphism and haplotype diversity comprising sequence-related genes and pseudogenes. Class II HLA DR molecules consist of noncovalent heteroduplexes derived from paired genes; a variable β-chain with a constant α-chain. Currently, more than 300 different alleles are recognized for the DRB1* locus (1). Exon 2 of this β-chain gene codes for many of the residues impinging on the peptide binding groove and has known nucleotide variants at more than one-third of 270 base positions. Except in rare homozygous individuals, genotyping of DRB1* produces frequent ambiguity because of shared sequence motifs among alleles and cis-trans uncertainty between polymorphisms. For histocompatibility typing, DRB1* alleles are traditionally partitioned into groups that reflect serologic lineages. High-resolution genotyping often requires haplotype isolation using group-specific PCR (2)(3) or other methods (4)(5) to exclude some alleles and reduce complexity. Primer sites for group-specific amplification have traditionally involved the hypervariable region at the 5′ end of exon 2. Blasczyk et al. (6) and Bergstrom et al.(7) have shown that sequence diversity within introns adjacent to exon 2 is also group-specific and can be used to separate alleles for unequivocal typing (8). Priming from intron sites increases the available region for primer design and expands the number of DRB group and subgroup sets. In addition, intron-primed amplicons include exon 2 in its entirety, defining polymorphisms obscured by, or external to, exon primers. We assessed a DRB1* typing strategy based on group-level resolution by sequence-specific oligonucleotide (SSO) hybridization, followed by sequencing …