Detection of autoantibodies to recombinant human thyroid peroxidase by sensitive enzyme immunoassay

Autoimmune response to the thyroid in humans: thyroid peroxidase--the common autoantigenic denominator

Autoimmunity to thyroid peroxidase (TPO), manifest as high affinity IgG class autoantibodies, is the common denominator of human thyroid autoimmunity, encompassing patients with overt hyper- or hypothyroidism as well as euthyroid individuals with subclinical disease. The identification and cloning of TPO (the "thyroid microsomal antigen") provided the critical tool for analyzing B and T cell reactivity to this major thyroid autoantigen. In particular, the availability of immunoreactive TPO permitted the isolation of essentially the entire repertoire of human monoclonal antibodies, a feat unparalled in an organ-specific autoimmune disease. These recombinant autoantibodies (expressed as Fab) provide insight into the genes encoding their H and L chains as well as the conformational epitopes on TPO with which serum autoantibodies interact. Analyses of TPO autoantibody epitopic "fingerprints" indicate a lack of epitope spreading as well as a genetic basis for their inheritance. Limited data are available for the responses and cytokine profiles of T cells to endogenously processed TPO. Moreover, the role of thyroid cells in initiating the autoimmune response to TPO, and of B cells in expanding and/or modulating the response of sensitized T cells, has yet to be established. Finally, because autoantibody (and likely T cell) responses to TPO parallel those to TSH receptor and thyroglobulin, manipulation of T and B cell responses to TPO may provide the basis for the development of immunospecific therapy for autoimmune thyroid disease in general.

Expression of human thyroid peroxidase in insect cells using recombinant baculovirus

The baculovirus expression system was used to overexpress recombinant human thyroid peroxidase. Sf-9 cells infected with the recombinant virus AcMNPV-hTPO synthesized hTPO protein (hTPO-bac) immunogenic on Western blots when probed with either rabbit anti-TPO peptide sera or pooled human anti-TPO sera (MS12/89). hTPO-bac was a major constituent of the membrane fraction from the infected cells, constituting 14.9% and 10.1% of the 1% deoxycholate-soluble and insoluble fractions, respectively, as judged by densitometry. Recombinant hTPO-bac was extracted from cellular membranes with 1% deoxycholate and partially purified by Sepharose 6B column chromatography. Specific immunoreactivity of MS12/89 to hTPO-bac on microtiter plates was seen using ELISA. Detergent extract from wild-type virus-infected Sf-9 cells was used as background control antigen; no specific reactivity to either hTPO-bac or control antigen was seen with control sera. To determine antigenic potency, MS12/89 was incubated with increasing concentrations of various preparations of hTPO antigen and with ovalbumin as control. The capacity of the partially purified hTPO-bac to immunoneutralize human anti-hTPO standard at 50% inhibition of binding was 0.01 U/microgram hTPO-bac (NIBSC Units), compared with 0.5 U/microgram and 0.06 U/microgram for natural hTPO and CHO-hTPO, respectively. When ELISA was performed using clinical samples of human sera to detect hTPO autoantibodies, results using hTPO-bac correlated well with those using hTPO from Graves' thyroid tissue (r = 0.85, p = 0.02) and those using recombinant hTPO from Chinese hamster ovary cells (hTPO-CHO) (r = 0.85, p = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous antigen presentation by autoantigen-transfected Epstein-Barr virus-lymphoblastoid cells. I. Generation of human thyroid peroxidase-reactive T cells and their T cell receptor repertoire

To develop a model for endogenous thyroid autoantigen presentation, we transfected EBV-transformed B lymphoblastoid cell lines (EBV-LCL), established from patients with autoimmune thyroid disease and normal controls, with cDNA for the human thyroid autoantigen thyroid peroxidase (hTPO). hTPO-antigen presentation to patient peripheral blood T cells was demonstrated after stimulation in vitro for 7 d with irradiated hTPO-transfected or untransfected autologous EBV-LCL. Anti-hTPO-reactive T cells were subsequently cloned in the presence of irradiated, autologous hTPO-transfected EBV-LCL and IL-2.10 T cell-cloned lines exhibited specific hTPO-induced proliferation (stimulation indices of 2.1-7.9) towards autologous hTPO-transfected EBV-LCL, and were subjected to human T cell receptor (hTCR) V gene analysis, using the PCR for the detection of V alpha and V beta hTcR gene families. The results indicated a preferential use of hTCR V alpha 1 and/or V alpha 3 in 9 of the 10 lines. In contrast, hTCR V beta gene family use was more variable. These data demonstrate a model for the endogenous presentation of human thyroid peroxidase in the absence of other thyroid specific antigens. The high frequency of antigen-specific T cells obtained from PBMC using this technique will facilitate further studies at both the functional and hTCR V gene level.

Expression of recombinant human thyroid peroxidase by the baculovirus system and its use in ELISA screening for diagnosis of autoimmune thyroid disease

The cDNAs coding for human full-length and soluble thyroid peroxidase (TPO) were constructed, cloned into a baculovirus transfer vector and used for infection of Spodoptera frugiperda (Sf9) cells. The soluble TPO lacking 87 amino acids of the C-terminal transmembrane and intracisternal domains was designed as a fusion protein with a histidine-hexapeptide as an affinity ligand at its C-terminus. Whereas the recombinant full-length TPO was expressed mainly in an insoluble form in Sf9 cells, the recombinant soluble TPO was almost completely secreted into the culture medium. Both the full-length and the soluble TPO were purified by conventional methods and by a specific affinity chromatography using metal chelating matrix respectively, and tested for their autoantigenicity towards anti-TPO autoantibodies. The ELISA established with the purified recombinant soluble TPO as antigen demonstrated its specificity, practicability and reproducibility in screening of anti-TPO autoantibodies in sera of autoimmune thyroid patients. High correlation (r = 0.89, n = 175) was obtained between the soluble TPO and natural TPO prepared from human thyroid glands. Pathological sera (n = 200) were positively assayed with a significance of 91%.

A 64 kDa membrane antigen is a recurrent epitope for natural autoantibodies in patients with Graves' thyroid and ophthalmic diseases

OBJECTIVE

We have explored the recently described 64 kDa extraocular muscle antigen that is associated with autoantibodies in the serum of patients with severe Grave's ophthalmopathy. The localization of the antigen and the specificity of autoantibodies for both eye muscle antigens and ophthalmopathy patients were investigated.

DESIGN

Western blotting and immunoprecipitation of metabolically labelled antigen from eye muscle and control tissues with sera from ophthalmopathy, Graves' without ophthalmopathy, and normals were used.

PATIENTS

Sera from normals (n = 9), patients with recent onset Graves' ophthalmopathy (n = 23), and patients with Graves' disease without ophthalmopathy (n = 8) were utilized.

MEASUREMENTS

Immunoblots using detergent phase separated (amphiphilic) antigen preparations from fetal eye muscle, skeletal muscle and control tissues were quantitated. Metabolically labelled eye muscle and skeletal muscle antigens were immunoprecipitated using patient and control IgG.

RESULTS

In the eye muscle detergent phase, immunoreactivity around 64 kDa was detected in 30% of the patients with ophthalmopathy (n = 23) as well as 38% of patients with Graves' disease and no ophthalmopathy (n = 8) and in 30% of normal sera (n = 9). There was significantly more of this anti-64 kDa reactivity in sera from the ophthalmopathy patients compared with the normals (P less than 0.01). 64 kDa reactivity to detergent phase antigens prepared from human thyroid, skeletal muscle, brain, and liver was also observed with these positive sera indicating the polyreactivity of the IgG interactions to conserved antigens in this region.

CONCLUSIONS

We conclude that IgG antibodies binding to a recurrent 64 kDa antigen are present in many normal human sera, with increased concentrations detectable in sera from Graves' ophthalmopathy patients. Such 'specificity-crossover' with similar molecular weight transmembrane antigens is likely to be caused by natural autoantibodies reacting with recurrent autoepitopes rather than a factor aetiological in the disease process.