Immunoglobulin GM and KM genotypes in Korean patients with systemic lupus erythematosus

Beyond Titer: Expanding the Scope of Clinical Autoantibody Testing

Background

Autoantibodies that bind self-antigens are a hallmark of autoimmune diseases, but can also be present in healthy individuals. Clinical assays that detect and titer antigen-specific autoantibodies are an important component of the diagnosis and monitoring of autoimmune diseases. Autoantibodies may contribute to disease pathogenesis via effector functions that are dictated by both the antigen-binding site and constant domain.

Content

In this review, we discuss features of antibodies, in addition to antigen-binding specificity, which determine effector function. These features include class, subclass, allotype, and glycosylation. We discuss emerging data indicating that analysis of these antibody features may be informative for diagnosis and monitoring of autoimmune diseases. We also consider methodologies to interrogate these features and consider how they could be implemented in the clinical laboratory.

Summary

Future autoantibody assays may incorporate assessment of additional antibody features that contribute to autoimmune disease pathogenesis and provide added clinical value.

Pathways: Strategies for susceptibility genes in SLE

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder marked by an inappropriate immune response to nuclear antigens. Recent whole genome association and more focused studies have revealed numerous genes implicated in this disease process, including ITGAM, Fc gamma receptors, complement components, C-reactive protein, and others. One common feature of these molecules is their involvement in the immune opsonin pathway and in phagocytic clearing of nuclear antigens and apoptotic debris, which provide excessive exposure of lupus-related antigens to immune cells. Analysis of gene-gene interactions in the opsonin pathway and its relationship to SLE may provide a system-based approach to identify additional candidate genes associated with disease able to account for a larger part of lupus susceptibility.

Development of two murine monoclonal antibodies recognizing human nG1m(a)-like isoallotypic markers

Antigenic determinants of immunoglobulin molecules are categorized into three groups: idiotypes, isotypes, and allotypes. An isoallotype is defined as an isotypic determinant in one or more subclasses and an allotype in another subclass of a given isotype. The isoallotype nG1m(a), formerly called non-a, is an allotype located on human IgG1 molecules lacking the G1m(a) allotype. This marker, however, is also detectable on all human IgG2 and IgG3 molecules. Anti-isoallotypic antibodies are useful tools for structural studies of immunoglobulins, forensic science, and epidemiological demographic investigations. In this study, two murine monoclonal antibodies (MAbs) recognizing nG1m(a)-like epitope(s) were generated against a human IgG myeloma protein. These MAbs are produced by hybridoma clones (4F18B12 and 6F18D1) obtained by fusion of SP2/0 myeloma cells with splenocytes from BALB/c mice immunized with heavy chain of a human IgG3 myeloma protein. These MAbs reacted with Fc, but not Fab fragment of the immunizing IgG3 paraprotein. Specificity of the MAbs was further analyzed using a panel of purified myeloma proteins and polyclonal IgG3, including IgG1 (n = 9), IgG2 (n = 4), IgG3 (n = 8), and IgG4 (n = 6) subclasses. Our results demonstrated that these MAbs reacted with linear epitope(s) located on heavy chain of all IgG2 and IgG3 molecules tested and some paraproteins of IgG1 subclass, but none of the IgG4 molecules. So these MAbs seem to recognize nG1m(a)-like isoallotypic marker. These MAbs showed no cross-reactivity with serum of other species tested. Both MAbs belonged to IgG1 subclass with affinity constants of 4.5 x 10(9) mol(-1) (4F18B12) and 3.46 x 10(9) mol(-1) (6F18D1), respectively. These MAbs might be used as a tool to detect nG1m(a) + IgG molecules.

Immunoglobulin gene polymorphisms are susceptibility factors in clinical and autoantibody subgroups of the idiopathic inflammatory myopathies

OBJECTIVE

To investigate possible associations of GM and KM markers with adult and juvenile forms of the idiopathic inflammatory myopathies (IIMs) in Caucasian and African American patients.

METHODS

We performed serologic analyses of polymorphic determinants associated with immunoglobulin gamma heavy chains (GM) and kappa light chains (KM) in large populations of Caucasian patients (n= 514 [297 adults and 217 children]) and African American patients (n=123 [73 adults and 50 children]) with IIM representing the major clinical and autoantibody groups.

RESULTS

For Caucasian patients with dermatomyositis (DM), the Gm 3 23 5,13 phenotype was a risk factor in both adults (odds ratio [OR] 2.2, corrected P [Pcorr]=0.020) and children (OR 2.2, Pcorr=0.0013). Of interest, the GM 13 allotype was a risk factor for juvenile DM in both Caucasian subjects (OR 3.9, Pcorr<0.0001) and African American subjects (OR 4.8, Pcorr=0.033). However, the Gm 1,3,17 5,13,21 phenotype was a risk factor for juvenile DM in Caucasian subjects but not African American subjects. Among the IIM autoantibody groups, Gm 3 23 5,13 was a risk factor in Caucasian adults with anti-Jo-1 autoantibodies (OR 3.4, Pcorr=0.0031), while the GM 3 allotype was protective in adults with anti-threonyl-transfer RNA synthetase or anti-U RNP autoantibodies (OR 0.1, Pcorr=0.047 and OR 0.2, Pcorr=0.034, respectively). In contrast, GM 6 was a risk factor in African American adults with anti-signal recognition particle autoantibodies (OR 7.5, Pcorr=0.041).

CONCLUSION

These data suggest that polymorphic alleles of GM and KM loci are differentially associated with IIM subgroups defined by age, ethnicity, clinical features, and autoantibody status, and expand the list of immune response genes that are possibly important in the pathogenesis of myositis.