Human organ-specific autoimmune disease. Molecular cloning and expression of an autoantibody gene repertoire for a major autoantigen reveals an antigenic immunodominant region and restricted immunoglobulin gene usage in the target organ

Rarity of autoantibodies to a major autoantigen, thyroid peroxidase, that interact with denatured antigen or with epitopes outside the immunodominant region

The nature of the autoantibody repertoire to the dominant autoantigen in human autoimmune thyroid disease is controversial. There is evidence that autoantibodies to thyroid peroxidase (TPO) interact with overlapping conformational epitopes in an immunodominant region and binding to denatured (DN) protein is decreased. Contrary data demonstrate TPO autoantibody reactivity with DN-TPO or polypeptide fragments. However, none of the TPO-specific, human monoclonal autoantibodies isolated to date preferentially recognize denatured autoantigen. We therefore searched an immunoglobulin gene phage display library for human autoantibodies that bind TPO denatured by reduction and alkylation (DN-TPO). Thyroid-infiltrating B cells from a typical TPO autoantibody-positive patient were the source of mRNA for library construction. Surprisingly, the library enriched after panning on DN-TPO, as well as a panel of individual clones, preferentially bound native (N)-TPO. Of 13 clones selected using DN-TPO or N-TPO, 12 clones recognized the TPO immunodominant region. Moreover, regardless of selection with N-TPO or DN-TPO, their heavy and light chains were encoded by similar VDJ and Vkappa combinations. One clone (DN4), isolated using DN-TPO, did not interact with the TPO immunodominant region and its H chain derives from a different VH gene. Although DN4 binds specifically to TPO, its affinity is low, unlike the high affinities of other human TPO autoantibodies. In conclusion, human monoclonal autoantibodies that preferentially recognize denatured TPO could not be isolated from an immunoglobulin gene library despite selection with denatured protein. Our findings demonstrate the bias of the human B cell repertoire towards recognition of an immunodominant region on the conformationally intact form of a major thyroid autoantigen.

A conformational B-cell epitope on the C-terminal end of the extracellular part of human thyroid peroxidase

To investigate the B-cell autoimmune epitopes on human thyroid peroxidase (TPO), we generated proteolytic peptides by enzymatic hydrolysis of TPO in nondenaturing and nonreducing conditions. The hydrolysate was chromatographed on a reverse phase column. We eluted a material immunoreactive with both a TPO monoclonal antibody recognizing a linear epitope (mAb47, amino acid 713-721) and TPO autoantibodies (aAb) from patients. The aAb immunoreactivity, but not that of mAb47, was lost after reduction. Western blots after electrophoresis without reduction showed that the aAb and mAb47 were immunoreactive with a 66-kDa band and that aAb identified a doublet at 20 kDa. For electrophoresis under reducing conditions, the 66-kDa band resolved into two peptides of 40 and 26 kDa, whereas the doublet at 20 kDa remained unchanged. None of these reduced peptides was immunoreactive with aAb, whereas the 40-kDa peptide was immunoreactive with mAb47. The 40-kDa peptide extends from amino acid 549 to 933 of TPO, and its last 192 amino acids overlap the autoimmune 20-kDa peptide. After iodine labeling, the 20-kDa peptide lost its immunoreactivity. We conclude that the C-terminal end of the extracellular part of TPO, which includes all the tyrosine residues of the 20-kDa peptide, contains at least one conformational B-cell epitope involved in autoimmune thyroid diseases.

Somatic hypermutation in autoimmune thyroid disease

Autoimmune thyroid disease is one of the most common autoimmune diseases. There is typically patient antibody (Ab) reactivity to one or more of the antigens thyroglobulin (Tg), thyroid peroxidase (TPO) and the thyroid simulating hormone receptor (TSHr). With the advent of combinatorial library technology, there has been an enormous increase in the number of sequences from Ab to Tg and TPO. The repertoire of both Tg and TPO Ab is restricted and indicates the importance of somatic hypermutation in the development of the high affinity Ab response. However, there are still too few sequences to determine patterns in which the mutation occurs, which residues are introduced during substitution and how individual substitutions affect the affinity of the Ab. Ab to the TSHr are of far greater pathological significance than those to Tg and TPO, but the current repertoire of Ab to the TSHr has yet to include the high affinity IgG Ab characteristic of patient serum Ab. Instructive analysis of the role of somatic hypermutation in the development of TSHr Ab therefore still awaits the isolation of the pathologically active repertoire. Despite this, the Ab response in thyroid autoimmunity remains one of the best characterised of human autoimmune diseases.

The human immune response to red blood cell antigens as revealed by repertoire cloning

A major goal of current immunologic research is to develop specific therapeutic strategies by which the enormous diversity in immune response can be enhanced, attenuated, or eliminated, depending on the particular disease process. For nearly a century, the human immune response to red blood cell antigens has served as a paradigm for understanding the pathophysiology of autoimmune disorders and alloimmune reactions to foreign cells and tissues. Recent developments in molecular biology have facilitated the expression of immune repertoires in the form of immunoglobulin Fab fragments on the surface of filamentous bacteriophage. Such approaches have provided powerful means for producing monoclonal antibodies for research, clinical, and therapeutic applications. Our laboratory has combined these techniques with novel cell-surface selection methods to isolate extraordinarily large arrays of human antibodies to the clinically relevant red blood cell Rh(D) antigen. Our results have provided a comprehensive genetic and serologic analysis of anit-Rh(D) antibodies within single alloimmunized individuals thereby offering new insights into the development of human immune repertoires.

Relationship between autoantibody epitopic recognition and immunoglobulin gene usage

An immunodominant region recognized by serum autoantibodies has been defined on the autoantigen thyroid peroxidase (TPO) using recombinant human TPO-specific Fab or a panel of mouse MoAbs. We have now analysed the epitopic relationships between the four recombinant Fab that identify the A and B domains of the TPO immunodominant region and (i) the mouse TPO MoAb as well as (ii) nine new TPO-specific Fab isolated independently. Competition between mouse MoAbs and recombinant Fab for binding to 125I-TPO revealed three patterns. First, for MoAbs 15, 59, 64 and 18, TPO binding was virtually abolished (approximately 90%) by Fab which define the A domain of TPO, with less inhibition by B domain Fab. Second, for MoAbs 2, 9 and 47, the Fab competed much less for TPO binding, and, when detectable, inhibition was predominantly with B domain Fab (65-20%). Third, for MoAbs 53, 30, 1, 24 and 40, none of the Fab competed effectively for 125I-TPO binding. Thus, the epitopes for MoAbs 18, 59, 64 and 15 correspond to those of the A domain defined by the human Fab, and the epitopes for MoAbs 2, 9 and 47 correspond to those of the B domain. In the second part of the study, competition studies demonstrated that the epitopes of nine new Fab corresponded to those of the four Fab that define the immunodominant region. For four new Fab, TPO binding was inhibited to a greater extent by B- than by A-domain Fab (65-95% versus <50%). In contrast, for five new Fab the A-domain Fab were more effective inhibitors (approximately 90%) than the B-domain Fab. In addition, consistent with previous observations, all five new Fab with 02/012 kappa L chains, but none of the new Fab with non-O2/O121 chains, interacted with A-domain epitopes. In conclusion, we have established the epitopic relationships between recombinant human Fab and mouse MoAbs that define the TPO immunodominant region on TPO. Further, analysis of recombinant TPO Fab isolated from patients on three continents strengthens the paradigm of a relationship between autoantibody epitopic recognition and immunoglobulin gene usage.

Unrestricted usage of immunoglobulin heavy chain genes in B cells infiltrating the wall of atherosclerotic abdominal aortic aneurysms

The aim of this study was to provide evidence for the hypothesis that the B cell rich infiltrate concentrated in the adventitia of atherosclerotic abdominal aortic aneurysms is an autoimmune response to specific tissue antigens. Detailed histological examination of biopsies from 26 atherosclerotic abdominal aortic aneurysms showed in the adventitia, the presence of lymphoid follicles in 7/26 (27%) and of plasma cells in all cases. DNA prepared from the outer aneurysm wall (n = 25) was amplified using the polymerase chain reaction to investigate the repertoire of the immunoglobulin heavy chain (VH) genes used. Amplification of the VDJ region of VH, using both framework 2 and 3 primers, revealed unrestricted usage of the VH gene in 24/25 cases. The only case where restricted usage of the VH genes was observed, might have been attributable to severe virally-induced tissue inflammation. These results indicate that, in the vast majority of atherosclerotic abdominal aortic aneurysms, the B cell rich adventitial infiltrates are not an autoimmune response to a limited repertoire of tissue antigens.

Analysis of immunoglobulin G kappa antithyroid peroxidase antibodies from different tissues in Hashimoto's thyroiditis

Antibodies (Ab) to thyroid peroxidase (TPO) are common in patients with autoimmune thyroid disease and may play a role in disease pathogenesis. We have prepared immunoglobulin G kappa (IgG kappa) and IgG lambda phage display combinatorial libraries from the cervical (thyroid-draining) lymph nodes of 2 Hashimoto's thyroiditis patients and from the thyroid of 1 patient. After selection with purified recombinant human TPO, up to 10 high affinity IgG kappa clones from each tissue source were analyzed further. No IgG lambda Fab were detected in the patient with the highest TPO Ab titer. Sequence analysis of the clones showed restricted heavy and light chain usage, similar to that in previously published TPO-reactive Fabs. This was despite the substantially larger sizes of the initial libraries, the use of lymph node tissue to generate libraries, and the analysis of the repertoire in patients with Hashimoto's thyroiditis rather than Graves' disease. There was overall similarity in sequences obtained from lymph node and thyroid libraries, with higher levels of somatic hypermutation in the former. The Fab inhibited binding of serum TPO Ab from five patients by 55-95%. These data together with those from previous reports indicate that although there is no unique Ab gene usage, there is the recurrent presence of certain variable regions in the high affinity TPO Ab response.

The epitopic "fingerprint" of thyroid peroxidase-specific Fab isolated from a patient's thyroid gland by the combinatorial library approach resembles that of autoantibodies in the donor's serum

A new thyroid peroxidase (TPO)-specific Fab (KM1) was obtained from an immunoglobulin gene combinatorial library of patient KM containing L chain genes amplified with a single "promiscuous" V kappa oligonucleotide primer. The KM1 L chain is encoded by a mutated B3 gene (V kappa IV family). Another mutated B3 L chain had been identified previously in a TPO-specific Fab (WR1.223) isolated from a different patient (WR). In contrast to patient KM, the WR L chains were amplified with a panel of V kappa family-specific primers. Both KM1 and WR1.223 bind TPO with high affinity (approximately 1 x 10(-9) M) and interact with an epitope in the B domain of the TPO immunodominant region. TPO-specific Fab previously isolated from a WR combinatorial library constructed with the promiscuous V kappa primer recognised the TPO A domain and none used a B3-like L chain. Remarkably, for both patients, Fab isolated from L chains generated with the promiscuous V kappa primer had epitopic profiles similar to autoantibodies in the donor's serum (KM-B domain; WR-A domain). Our data indicate that the promiscuous primer preferentially amplifies the dominant L chain present in vivo. However, to obtain a relatively rare Fab (such as the B domain Fab from WR), family-specific kappa primers are required. These findings provide insight into the relationship between TPO autoantibody gene usage, epitopic recognition, and the effectiveness of the combinatorial library approach.

Immunoglobulin G kappa antithyroid peroxidase antibodies in Hashimoto's thyroiditis: epitope-mapping analysis

Patients with autoimmune thyroid disease frequently have high affinity antibodies to thyroid peroxidase (TPO), although the role they play in disease pathogenesis is not known. We have previously prepared 37 monoclonal anti-TPO IgG kappa Fab fragments from two patients with Hashimoto's thyroiditis and demonstrated the similarity of these Fab sequences to those published previously, mainly derived from patients with Graves' disease. In this paper, we described epitope mapping of these Fabs using a previously characterized panel of murine monoclonal antibody (mAb) and show that the Fabs bind to two neighboring epitopes on native TPO. Although the epitope-mapping method differs from that used to characterize previously published TPO-reactive Fab sequences, it indicates a similarly restricted response to neighboring epitopes in both Graves' disease and Hashimoto's thyroiditis. The epitope mapping included mAb 47, which binds to a linear TPO peptide of known sequence in addition to native TPO. Although TPO-reactive Fab did not inhibit the binding of mAb 47, mAb 47 did inhibit the binding of Fab, indicating the likely site of the immunodominant region on native TPO. These results confirm the restricted nature of TPO antibody and further delineate the immunodominant region of native TPO as defined by the mAb.

Molecular cloning of anti-SS-A/Ro 60-kDa peptide Fab fragments from infiltrating salivary gland lymphocytes of a patient with Sjögren's syndrome

Anti-SS-A/Ro antibodies are commonly found in systemic autoimmune diseases such as Sjögren's syndrome and systemic lupus erythematosus, and some of these antibodies appear to be responsible for certain pathological lesions including congenital heart block in neonatal lupus. In this study, we generated three human antibody Fab fragments that specifically bind to SS-A/Ro 60-kd peptide from salivary gland lymphocytes of a patient with Sjögren's syndrome by using a phage-display technique. Sequence analysis demonstrated that two of the three Fab clones (E-42 and E-60) used homologous heavy chains derived from the germline VH gene DP73 in combination with different light chains which were derived from germline V kappa gene L6 and V lambda gene DPL23. The third Fab clone (E-56) used another heavy chain derived from the germline VH gene DP31 in combination with the identical light chain as that of E-42. All three Fab clones revealed a high number of somatic mutations that likely occurred in the context of antigen selection. These findings suggest the restricted usage of VH and VL genes of anti-SS-A/Ro antibodies in salivary gland lymphocytes of the patient.

Insight into screening immunoglobulin gene combinatorial libraries in a phage display vector: a tale of two antibodies

Combinatorial libraries of immunoglobulin genes in "phage display" vectors are a powerful tool for obtaining antigen-specific antibody fragments. To date, this approach has been used to isolate abundant, but not rare, human autoantibodies of IgG class. We have compared the relative efficiencies of panning pComb3 libraries made from intrathyroidal plasma cells for abundant human autoantibodies to thyroid peroxidase (TPO) and rare autoantibodies to the thyrotropin receptor (TSHR). TPO-specific Fab were readily obtained from a library using three different forms of recombinant antigen, (i) purified TPO, (ii) impure TPO in culture medium and, (iii) TPO expressed on the surface of CHO cells. In contrast, TSHR-specific Fab were not isolated. This was the case despite repeated pannings of six libraries from three optimal patients (IgG/kappa and IgG/lambda libraries for each patient). Both purified recombinant TSHR and CHO cells expressing TSHR on their surface were used. Library enrichment was observed on some screenings. However, Fab expressed by individual clones or from enriched libraries were not specific as determined by (i) binding to purified, radio-labeled antigen, (ii) FACS analysis of TSHR on intact CHO cells and, (iii) inhibition of radiolabeled TSH binding. Remarkably, in screening for both TPO- and TSHR-specific Fab, neither library enrichment nor the retention of cDNA inserts of the correct size correlated with obtaining Fab with the antigenic specificity sought. Indeed, excellent enrichment could be observed with conditioned medium from untransfected cells. Our data suggest that the key to isolating rare antibodies from phage display libraries is not the creation of vast libraries of greater diversity or even the development of more stable vectors. Rather, success in this endeavor appears to require reducing the "noise" of non-specific clones in a moderately sized library.

Autoantibody-mediated capture and presentation of autoantigen to T cells via the Fc epsilon receptor by a recombinant human autoantibody Fab converted to IgE

Fc epsilon receptor (CD23)-mediated capture of IgE-antigen complexes by B cells provides a powerful antigen presenting system. Our goal was to develop a system using high affinity, human, organ-specific monoclonal autoantibodies for antigen capture by B cells. For this purpose, we converted a recombinant human autoantibody to TPO from a Fab (SP1.4) to an IgE molecule. Sera from all patients with autoimmune thyroid disease contain autoantibodies with the same epitope as SP1.4. The SP1.4 H and L chain V region genes were spliced by overlap PCR to a mammalian, non-immunoglobulin signal peptide and transferred to expression vectors for human IgG1 and kappa, respectively. After inserting the IgE constant region genes into the H chain vector, the kappa and IgE H chain vectors were expressed in SP2/0 cells. SP1.4-IgE retains its high affinity (Kd) for TPO (approximately 2 x 10(-10) M), recognizes the same epitope as Fab SP1.4 and, importantly binds to a different epitope than does Fab TR1.9. Binding of preformed complexes of SP1.4-IgE and biotinylated TPO to EB virus transformed B cells (EBVL) was weakly detectable by flow cytometry and was displaced by unlabeled TPO. SP1.4-IgE/125I-TPO complex binding to EBVL was much more clearly evident, was also inhibited by the addition of unlabeled TPO, and was greatly reduced by preincubation of the EBVL with anti-CD23. Further, autologous EBVL preincubated with SP1.4-IgE/TPO complexes stimulated proliferation of TPO-specific T cells. IgE autoantibody-mediated antigen focusing to B cells is unlikely to operate in vivo but is, instead, a powerful investigative tool. In conclusion, SP1.4-IgE is the first monoclonal human autoantibody to be developed for IgE-mediated antigen presentation to T cells by EBVL. Recombinant human autoantibodies converted to IgE, possibly in combinations if their epitopes permit simultaneous binding to the same molecule, provide a unique system to generate human T cell lines and clones specific for peptides naturally processed from internalized high affinity autoantibody/autoantigen complexes.

Structural studies of human autoantibodies. Crystal structure of a thyroid peroxidase autoantibody Fab

The three-dimensional structure of the Fab of TR1.9, a high-affinity IgG1, kappa human autoantibody to thyroid peroxidase, was determined crystallographically to a resolution of 2.0 A. The combining site was found to be relatively flat, like other antibodies to large proteins. Sequence differences from the most closely related germline genes mainly occur at positions occupied by residues with outward-pointing side chains. An increased deformability of the second and third complementarity-determining regions of the heavy chain may result from the replacement of two germline asparagines and the presence of several glycines, and may allow "induced fit" in the binding to antigen. Four exposed charged residues, resulting from the use of a particular D (diversity) and J (joining) segments in the assembly of the heavy chain, may contribute to the high affinity of antigen binding. The crystal structure of TR1.9 Fab is the first for a human IgG high-affinity autoantibody.

Unique autoantibody epitopes in an immunodominant region of thyroid peroxidase

To define the autoantibody epitopes in amino acids 513-633 of thyroid peroxidase (TPO), a region frequently recognized in thyroiditis, cDNA sequences coding for peptide fragments of this region were amplified and ligated into pMalcRI and pGEX vectors for expression as recombinant fusion proteins. Western blots and enzyme-linked immunosorbent assay were then used to examine the reactivity in sera from 45 Hashimoto's and 47 Graves' disease patients. Two autoantibody epitopes within TPO amino acids 589-633 were identified; 16 of 35 patients reactive to TPO513-633 recognized the epitope of TPO592-613, while 6 patients recognized the epitope of TPO607-633. Eleven other patients with thyroiditis and two with Graves' disease recognized only the whole 589-633 fragment, and this response accounted for the Hashimoto's disease specificity. An amino acid sequence comparison of TPO592-613 with analogous regions of other peroxidase enzymes revealed significant differences in this area, and the substitution of even a single amino acid in one of the epitopes markedly decreased the binding affinity of autoantibodies. Additionally, the exclusive recognition by patients of only one of the epitopes within this region suggests a genetic restriction of the autoantibody response.

Influence of the light chain repertoire on immunoglobulin genes encoding thyroid autoantibody Fab from combinatorial libraries

The diversity of the immunoglobulin heavy (H) and light (L) gene libraries used to construct a combinatorial library is an important parameter in determining the characteristics of antigen-specific Fab obtained from the library. To investigate the role of library diversity, we compared Fab specific for the autoantigen thyroid peroxidase (TPO) isolated from two different combinatorial libraries. Both libraries contained the same H chain genes. The original combinatorial library (H/R) utilized kappa chains generated using a single kappa variable region oligonucleotide primer. We constructed a second combinatorial library (H/D) containing kappa chains amplified with a diverse panel of variable region primers. From the the original H/R library, only two groups of TPO-specific Fab had been obtained, involving two H chain types (V1-3B and hv1L1) but only one kappa chain type (012). In contrast, among the seven TPO Fab characterized from the second library (H/D) we observed five different VH/VL combinations, comprising three types of H chains (V1-3B, VH26 and DP7) and four types of kappa chains (O12, L12, L2/hv328H5 and B3). Besides differences in VH and VL genes, as well as VH/VL combinations, the new TPO Fab used different D regions and JH and JK elements. Nevertheless, the new kappa Fab resembled previously isolated TPO Fab in terms of their affinity for TPO (Kd approximately 10(-9)M) and preferential recognition of conformationally intact autoantigen. In summary, our studies demonstrate that the diversity of the L chain library repertoire, while having little effect on immunological properties, has a major influence on the genes encoding antigen-specific Fab selected from a combinatorial library. For the successful isolation of rare but clinically important autoantibodies (such as to the TSH receptor) by the combinatorial library approach, library diversity is likely to be a major factor.

Molecular cloning and characterization of human thyroid peroxidase autoantibodies of lambda light chain type

IgG class thyroid peroxidase (TPO) autoantibodies with kappa light (L) chains predominate in serum and the genes for a large repertoire of such autoantibodies have been characterized. The present study was performed to clone and characterize TPO autoantibodies with lambda L chains which comprise approximately 20% of serum TPO autoantibodies. From a combinatorial IgG H/lambda L chain cDNA library in the phage display vector pComb3, 24 TPO-binding clones with lambda L chains were isolated, comprising three different heavy (H) and light (L) chain combinations. These combinations utilized two genes from the Vlambda II and IIIb families (closest germline genes DPL11 and hsigg11150) and three genes from the VH1, VH3 and VH4 families (VH26, 4.34 and hv1L1). The deduced amino acid sequences of these H chains were quite different from those of kappa F(ab) isolated using the same H chain library. We expressed the proteins for these three lambda F(ab), as well as for a lambda F(ab) (Humlv318 L chain/DP10-like H chain) previously isolated from another patient. The affinities for TPO of the lambda F(ab) (Kd 8 x 10(-10) M to 10(-7) M) were lower than those of the kappa F(ab) (Kd approximately 10(-10) M). For two lambda F(ab), both H and L chain genes were close to germline configuration, but there was no straightforward relationship between the extent of somatic mutation from germline configuration and affinity for TPO. All four lambda F(ab) bound less well to denatured TPO as to native TPO. The three F(ab) for which sufficient protein could be expressed for competition studies all recognized domain B within the immunodominant region on TPO previously identified using F(ab) with kappa L chains. Aside from these TPO-specific F(ab), only a few other human IgG class, organ-specific autoantibodies with lambda L chains have been characterized at the molecular level. Our study significantly augments the small database on this category of autoantibodies in general.

Genetic and epitopic analysis of thyroid peroxidase (TPO) autoantibodies: markers of the human thyroid autoimmune response

TPO autoantibodies, the hallmark of human autoimmune thyroid disease, are of IgG class and are associated with thyroid destruction and hypothyroidism. Using the immunoglobulin gene combinatorial library approach, a panel of human monoclonal TPO autoantibodies (expressed as Fab) has been generated from thyroid tissue-infiltrating B cells. TPO-specific Fab closely resemble patients' serum autoantibodies in terms of L chain type, IgG subclass, affinities for TPO as well as epitopes recognized by > 80% of TPO autoantibodies in an individual's serum. TPO autoantibody V region genes are not unique; H chain V genes are usually mutated, while L chain V genes are sometimes in germ-line conformation. The autoantibodies recognize an immunodominant region involving conformational, overlapping epitopes in domains A and B. Finally, TPO autoantibody epitopic fingerprints are distinctive for individual sera, are not associated with hypothyroidism, but are conserved over time (indicating a lack of B cell epitope spreading). Evidence for conservation as well as inheritance of the fingerprints in some families, together with VH gene polymorphisms, may provide insight into the genetic basis of human autoimmune thyroid disease. Furthermore, monoclonal human TPO autoantibodies will be invaluable for B cell presentation of TPO to determine the T cell epitopes involved in TPO autoantibody production.

Analysis of the V kappa I family: germline genes from an SLE patient and expressed autoantibodies

Our studies of anti-DNA antibodies in systemic lupus erythematosus have demonstrated a preferential use of the V kappa I family to encode light chains of antibodies that express the anti-DNA associated 3I idiotype. This idiotype is present on a high percentage of anti-DNA antibodies in approximately 80% of SLE patients1,2. In this study, we employed PCR to obtain V kappa I germline genes from a lupus patient in order to address the following questions: Do the V kappa I germline genes of an individual with autoimmune disease differ from those of healthy individuals? What V kappa I genes are used to encode autoantibodies and are they used to encode protective antibodies also? Does the V kappa I gene family display peculiarities in V gene segment rearrangement or somatic mutation? Our analysis shows that the coding region sequences of germline genes of an autoimmune individual are highly homologous to those of non-autoimmune individuals. In addition, the same germline genes can be utilized to encode antibodies to both exogenous and self antigens. While rearranged V kappa genes are ordinarily derived from the J kappa proximal region of the V kappa locus, V kappa I genes encoding autoantibodies derive primarily from the J kappa distal region. It is not yet clear if this applies equally to V kappa I encoded antibodies directed to foreign antigen.

Combinatorial libraries: new insights into human organ-specific autoantibodies

The recent application of immunoglobulin (Ig) gene combinatorial library technology has led to a logarithmic increase in information concerning human, disease-associated, organ-specific autoantibodies of the IgG class. As reviewed here by Basil Rapoport, Stefano Portolano and Sandra McLachlan, the molecular cloning, analysis and expression of the genes for increasing numbers of these human, monoclonal autoantibodies is providing new insight into the genetic background and epitopic repertoires of such molecules.

Lymphocytic traffic and homing into target tissue and the generation of endocrine autoimmunity

Endocrine autoimmunity is known to be characterized by the presence of specific autoantibodies and from the histopathological point of view by lymphocytic infiltration in the target tissue. The presence of mononuclear cell infiltrates is the pathological hallmark of most endocrine diseases characterized by an autoimmune process directed against antigens expressed on endocrine cells. Infiltrating cells can usually be detected by biopsy or by using other, non-invasive, techniques. However, in endocrine tissue such as the islets of Langerhans and the adrenal glands it is difficult to perform biopsies and diagnosis of the autoimmune process is dependent mainly upon detection of specific autoantibodies. A crucial aspect of endocrine autoimmunity and of all processes of organ specific autoimmunity is why and how lymphocytes migrate from primary lymphoid tissue to their specific targets. This occurs mainly through contact with specific adhesion molecules which enable lymphocytes to adhere to the endothelial vessels in close proximity to the target tissue. In this review we discuss the homing of peripheral mononuclear cells into target endocrine tissues and the mediating role of adhesion molecules.

Isolation and characterization of a monoclonal human thyroid peroxidase autoantibody of lambda light chain type

Thyroid peroxidase (TPO) autoantibodies, a hallmark of human autoimmune thyroid disease, may have kappa or lambda light chains. Monoclonal human TPO autoantibodies with kappa light chains have previously been developed by cloning and expressing "combinatorial" libraries of immunoglobulin genes in bacteria. In the present study, an IgG1/lambda combinatorial library was generated from thyroid cDNA of a Graves' patient whose serum contained lambda TPO antibodies. Screening the bacteriophage library with 125I-TPO yielded one clone, TR1.41. The oligonucleotide sequence of TR1.41 was determined and the nature of its interaction with TPO was investigated. The affinity of TR1.41 for TPO is high (Kd approximately 10(-9) M), comparable to that of monoclonal kappa TPO autoantibodies derived from the same patient. The genes encoding the heavy and light chains of TR1.41 differ in a number of respects from the closest available germline genes. Such differences are consistent with somatic mutation in a high-affinity antibody. An important characteristic of TR1.41 is its interaction with the immunodominant domain on TPO recognized by approximately 80% of serum TPO autoantibodies. The frequency of TPO-specific F(ab) generated from the thyroid gland of patient TR was much lower for F(ab) with lambda light chains (1:150,000) than for F(ab) with kappa light chains (1:13,000). Despite this low frequency, the high affinity of TR1.41 and its recognition of the immunodominant region on TPO indicate that lambda autoantibodies of this type may represent an important constituent of the TPO autoantibody response in man. In conclusion, this is the first report on the molecular cloning and characterization of a thyroid autoantibody of lambda L chain type by the combinatorial library approach.

Variable region sequences and idiotypic expression of a protective human immunoglobulin M antibody to capsular polysaccharides of Neisseria meningitidis group B and Escherichia coli K1

We determined the heavy (H)- and light (L)-chain variable (V) region nucleotide and translated amino acid sequences of the human immunoglobulin M(kappa) monoclonal antibody (MAb) 5E1, which is specific for the polysaccharide capsule of Escherichia coli K1 and Neisseria meningitidis group B (poly[alpha(2-->8)-N-acetylneuraminic acid]) and which is protective in animal models of infection. The 5E1 VH gene is a member of the VHIIIb family and is 97% homologous to the 9.1 germ line gene. The 5E1 VL gene is a member of the kappa I subgroup and is 98% homologous to the germ line gene, 15A, also known as KLO12. The VL and/or VH genes used by 5E1 are highly homologous to the V genes encoding antibodies to the Haemophilus influenzae type b polysaccharide and to antibodies reactive with self-antigens such as erythrocyte "i," DNA, and thyroid peroxidase. We also produced three murine anti-idiotype (Id) MAbs against 5E1. All three anti-Ids recognize a minor subset of antimeningococcal B polysaccharide antibodies present in serum from normal adults. Two of the anti-Ids define distinct Ids associated with antibodies having kappa I-15A V regions. These 15A-associated Ids are expressed by some heterologous human antimeningococcal B polysaccharide MAbs, and they also are independently expressed by two human MAbs that are specific for either the H. influenzae b polysaccharide or the i erythrocyte antigen and that utilize the kappa I-15A V region. Taken together, these data indicate that the 5E1 antibody uses V regions that recur in the human antibody repertoires to this polysaccharide and to structurally dissimilar polysaccharides and autoantigens. Thus, the poor immunogenicity of poly[alpha(2-->8)-N-acetylneuraminic acid] cannot be explained by the unavailability of certain critical VH and VL genes required for generation of antibody response.

Immunoglobulin A in Graves' orbital tissue: deoxyribonucleic acid amplification by polymerase chain reaction

A role for IgA autoantibodies in Graves' ophthalmopathy is suggested by the presence of immunoglobulins of this class in Graves' orbital tissue, as detected by immunohistochemistry. We, therefore, investigated the possibility of using the polymerase chain reaction (PCR) to amplify IgA immunoglobulin genes from plasma cells infiltrating Graves' eye tissue. Template cDNA was reverse-transcribed from orbital muscle (M) mRNA of one patient (#7) and from orbital connective tissue/fat (F) mRNA of two patients (#1 and #7), both undergoing surgery for exophthalmos because of severe infiltrative ophthalmopathy. Preliminary studies to establish the PCR procedure were performed for kappa light chain DNA amplification. With the very small amount of orbital tissue template available, the sensitive "hot start" modification of the PCR was necessary to amplify significant amounts of kappa light chain DNA. Using this procedure, IgA heavy chain DNA was amplified from both connective tissue/fat (F7) and muscle (M7) cDNA of patient #7. The DNA yield was less for IgA than for IgG using the same template. There was no significant IgA (or IgG) DNA product using the connective tissue/fat cDNA of patient #1. While not implying that IgA-infiltrating plasma cells are specific for Graves' orbital tissue, our studies nevertheless demonstrate the feasibility of amplifying the genes coding for IgA antibodies from Graves' orbital tissue plasma cells. Expression of these immunoglobulin genes in future studies will make it possible to determine the antigen specificity of the antibodies expressed by Graves' orbital tissue plasma cells.

Cloning and characterisation of TPO autoantibodies using combinatorial phage display libraries

Thyroid lymphocyte RNA from a Hashimoto patient with high serum levels of autoantibodies to thyroid peroxidase (TPO) was used to construct a phage display antibody library in the phagemid vector pComb3. The library (100,000cfu) encoded IgG1 heavy chains together with kappa light chains. Selection of the phages displaying TPO antibody on TPO-coated ELISA plates yielded a phage population enriched for surface expression of TPO antibody Fabs. 3 different Fabs specific for TPO were subsequently isolated with affinities in the region of 10(9) molar-1. 2 of the Fabs recognised the same, or closely related, epitopes on TPO whereas the third Fab recognised a different epitope. These 2 epitopes were recognised by TPO autoantibodies in the serum of the lymphocyte donor and a series of 10 patient sera. Available sequence data showed that several non-self antibodies and non-thyroid autoantibodies use the same V kappa and VH germline genes as TPO autoantibodies. There appeared to be no clear relationship between gene sequence or gene family usage by TPO autoantibodies of the same or similar epitope specificity.

An analysis of the structure and antigenicity of different forms of human thyroid peroxidase

Thyroid peroxidase (TPO) is an important enzyme in the production of thyroid hormone and one of the major autoantigens in autoimmune thyroid disease. The gene for human thyroid peroxidase encodes a single 933 amino acid polypeptide chain. However, several reports have suggested that it exists in both high- and low-molecular-weight forms and the exact structure of the native enzyme is not known. We examined the structure of TPO using two monoclonal antibodies against different portions of TPO, a polyclonal mouse antiserum raised against a 300 amino acid fragment of TPO and autoantibodies directed against TPO obtained from patients with autoimmune thyroid disease. Western blots performed under nonreducing conditions identified three bands of approximately 220-230 kDa and two bands of 105 and 110 kDa that appeared to be immunologic TPO. After reduction, the TPO activity migrated as a smear of bands from 105 to 110 kDa, suggesting that the higher molecular weight form of the enzyme is a disulfide-linked dimer. Patients with autoimmune thyroid disease showed higher rates of recognition of the dimer than the reduced monomer when serologic reactivity was analyzed by Western blots. Eighty-three percent (40 of 48) of patients with Graves' disease and 76% (34 of 45) of Hashimoto's disease patients recognized the dimer form of TPO, while 48% (23 of 48) of Graves' and 60% (27 of 45) of Hashimoto's patients recognized reduced monomer TPO, even though both forms were denatured with SDS. Antibodies against different portions of the TPO chain all bound to the 105 kDa bands, indicating that the TPO chain is not bisected during posttranslational processing.(ABSTRACT TRUNCATED AT 250 WORDS)