Correlations of autoimmunity with H-2 and T cell receptor beta chain genotypes in (NZB X NZW) F2 mice

Genomic absence of the gene encoding T cell receptor Vbeta7.2 is linked to the presence of autoantibodies in Sjögren's syndrome

OBJECTIVE

It is not yet known whether the absence of certain T cell receptor V(beta) (TCRBV) genes (e.g., due to genomic deletion) has functional significance. We examined this question in relation to a known 21.6-kb insertion/deletion-related polymorphism (IDRP) in the human BV locus.

METHODS

New polymerase chain reaction (PCR) genotyping methods were used. Monoclonal antibodies to TCRBV gene products were used to confirm the absence of the relevant proteins. Patients with Sjögren's syndrome (SS) or systemic lupus erythematosus (SLE) were compared with normal controls with regard to TCR genotypes and serologic profiles.

RESULTS

There are 3 known haplotypes (I, D1, D2) and 6 possible genotypes related to the 21.6-kb IDRP. Novel PCR-based methods were used to define these genotypes. In subjects with deleted/deleted (D/D) genotypes, T cells could not express V(beta)7.2 TCRs, as assayed with a new antibody specific for V(beta)7.2. This was the sole significant difference between subjects without the insertion and those with either 1 or 2 copies. Surprisingly, we found that the D/D genotype was associated with primary SS, but only when pathogenic autoantibodies were present.

CONCLUSION

These results suggest that T cells expressing TCRs with V(beta)7.2 are protective against a pathogenic immune response in SS. Thus, genomic polymorphism of TCR genes (along with the correct HLA alleles) determines whether T cells can direct a pathogenic autoimmune response.

Anti-DNA autoantibodies and systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease that affects most of the organs and tissues of the body, causing glomerulonephritis, arthritis, and cerebritis. SLE can be fatal with nephritis, in particular, predicting a poor outcome for patients. In this review, we highlight what has been learned about SLE from the study of mouse models, and pay particular attention to anti-DNA autoantibodies, both as pathological agents of lupus nephritis and as DNA-binding proteins. We summarize the current approaches used to treat SLE and discuss the targeting of anti-DNA autoantibodies as a new treatment for lupus nephritis.

Biochemical and Functional Analyses of Chromatin Changes at the TCR-β Gene Locus During CD4−CD8− to CD4+CD8+ Thymocyte Differentiation

Allelic exclusion is the process wherein lymphocytes express Ag receptors from only one of two possible alleles, and is effected through a feedback inhibition of further rearrangement of the second allele. The feedback signal is thought to cause chromatin changes that block accessibility of the second allele to the recombinase. To identify the putative chromatin changes associated with allelic exclusion, we assayed for DNase I hypersensitivity, DNA methylation, and transcription in 100 kb of the TCR-β locus. Contrary to current models, we identified chromatin changes indicative of an active and accessible locus associated with the occurrence of allelic exclusion. Of 11 DNase I hypersensitive sites identified, 3 were induced during CD4−CD8− to CD4+CD8+ thymocyte differentiation, and demethylation and increased germline transcription of the locus were evident. We further examined the role of the most prominently induced site near the TCR-β enhancer (Eβ) in allelic exclusion by targeted mutagenesis. Two other sites were also examined in New Zealand White (NZW) mice that have a natural deletion in the TCR-β locus. TCR-β gene recombination and allelic exclusion were normal in both mutant mice, negating dominant roles for the three hypersensitive sites in the control of allelic exclusion. The data suggest that alternative cis-regulatory elements, perhaps contained in the Eβ enhancer and/or in the upstream Vβ region, are involved in the control of TCR-β allelic exclusion.

Role of the major histocompatibility complex class II Ea gene in lupus susceptibility in mice

The gene(s) encoded within major histocompatibility complex (MHC) act as one of the major genetic elements contributing to the susceptibility of murine systemic lupus erythematosus (SLE). We have recently demonstrated that lupus susceptibility is more closely linked to the I-E- H-2(b) haplotype than to the I-E+ H-2(d) haplotype in lupus-prone BXSB and (NZB x BXSB)F1 hybrid mice. To investigate whether the reduced susceptibility to SLE in H-2(d) mice is related to the expression of the MHC class II Ea gene (absent in H-2(b) mice), we determined the possible role of the Ea gene as a lupus protective gene in mice. Our results showed that (i) the development of SLE was almost completely prevented in BXSB (H-2(b)) mice expressing two copies of the Ead transgene at the homozygous level as well as in BXSB H-2(k) (I-E+) congenic mice as for H-2(d) BXSB mice, and (ii) the expression of two functional Ea (transgenic and endogenous) genes in either H-2(d/b) (NZB x BXSB)F1 or H-2(k/b) (MRL x BXSB)F1 mice provided protection from SLE at levels comparable to those conferred by the H-2(d/d) or H-2(k/k) haplotype. In addition, the level of the Ea gene-mediated protection appeared to be dependent on the genetic susceptibility to SLE in individual lupus-prone mice. Our results indicate that the reduced susceptibility associated with the I-E+ H-2(d) and H-2(k) haplotypes (versus the I-E- H-2(b) haplotype) is largely, if not all, contributed by the apparent autoimmune suppressive effect of the Ea gene, independently of the expression of the I-A or other MHC-linked genes.

Analysis of Vbeta4 T cell receptor CDR3 repertoire in BALB/c and (NZB x NZW)F1 mice

To examine the unique TCR repertoire in auto-immune-prone (NZB x NZW)F1 (B/WF1) mice, we analysed the Vbeta4 CDR3 region of TCRbeta chain in spleens of young (1 month old) and aged (6 month old) BALB/c and B/WF1 mice. Total RNA from spleens was used for cDNA synthesis and TCRVbeta4 PCR products were cloned and sequenced. Young B/WF1 mice showed high frequency (38.5%) of anionic amino acid residues at position beta100 in TCRVbeta4 chain compared to that (19.0%) in young BALB/c mice. Aged BALB/c mice and B/WF1 mice showed increase of frequency (38.1 and 51.9%, respectively) of anionic residues at beta100. These results indicate that Vbeta4-T cells that have anionic residues at beta100 in CDR3 region of TCRbeta chain increase with age in normal mice. Auto-immune prone mice show high frequency of anionic residues at beta100 in TCRVbeta4 chain even at the age of 1 month. These T cells may interact with cationic self-antigen(s) and might contribute to the onset and/or the progression of systemic autoimmunity in concert with other genetic elements in B/WF1 mice.

A genetically determined insertion/deletion related polymorphism in human T cell receptor beta chain (TCRB) includes functional variable gene segments

Polymorphism in the human T cell receptor beta chain (TCRB) gene complex includes haplotypes with different numbers of TCRBV genes. An insertion/deletion related polymorphism (IDRP) in the human TCRBV region was found to involve TCRBV gene segments. Inserted TCRB haplotypes contain an additional 21.5 kb in which three TCRBV genes are encoded, members of the TCRBV7, TCRBV9, and TCRBV13 families. Two TCRBV gene segments were present only in inserted haplotypes; one of these, TCRBV7S3, is a functional gene and the other, TCRBV9S2(P), is a pseudogene because of an inframe termination colon. In addition, inserted haplotypes contain two identical copies of the TCRBV13S2 gene, whereas deleted haplotypes have only one copy. Deleted haplotypes could be subdivided into two types, deleted*1 and deleted*2, on the basis of sequence variations in TCRBV6S7 and TCRBV13S2 genes. Both deleted*1 and deleted*2 haplotypes contained the same number of TCRBV genes; both contain 60 genes of which 50 are functional, whereas, inserted haplotypes contained 63 genes of which 52 are functional. Comparisons of inserted region sequences with the homologous region in a deleted haplotype, and with sequences surrounding related TCRBV genes, revealed patterns of similarity that suggest insertion as well as deletion events have occurred in the evolution of the TCRBV gene complex. These data indicate that the genomic TCR repertoire is expanded in individuals who have inserted TCRBV haplotypes. The presence of additional TCRBV genes or, alternatively, the absence of certain TCRBV genes may have an impact upon immune responses and susceptibility to autoimmune diseases.

The Y chromosome-linked "autoimmune accelerating" yaa gene suppresses collagen-induced arthritis

The Y-linked autoimmune accelerating gene mutation (yaa), first discovered in the BXSB mouse strain, is known to accelerate spontaneous autoantibody production and subsequent development of lupus disease. We have investigated the role of the yaa gene in the development of the type II collagen (CII)-induced arthritis (CIA), which is used as a model for rheumatoid arthritis. In contrast to the accelerating effects on development of lupus autoimmunity we can show that the presence of BXSB Y chromosome carrying the yaa gene block development of CIA in F1 crosses with three normally CIA-susceptible strains, DBA/1, C3H.Q and B10.Q. Backcross experiments showed an additional modulatory effect from other BXSB genes or possibly from DBA/1 X chromosome. To evaluate the effect mediated by the yaa gene alone, the BXSB Y chromosome was bred into the DBA/1 gene background. The DBA/1 congenic DBA/1.yaa male mice were less susceptible to arthritis development than their DBA/1 counterparts. (B10.QxDBA/1.yaa)F1 acquired resistance to arthritis development similar to that of DBA/1.yaa, indicating a role for the yaa gene alone. The serum levels of autoantibodies to CII were significantly suppressed in all strains carrying yaa. In DBA/1.yaa mice a reduced number of T cells were found to produce interferon-gamma after in vitro stimulation with CII. Thus, although autoreactive B cells are important in both diseases they play different roles in murine lupus and in CIA.

Major histocompatibility complex controls clonal proliferation of CD5+ B cells in H-2-congenic New Zealand mice: a model for B cell chronic lymphocytic leukemia and autoimmune disease

By employing H-2-congenic NZB, NZW and (NZB x NZW)F1 mice with either the homozygous H-2d/H-2d, H-2z/H-2z or heterozygous H-2d/H-2z haplotype, we found that in the spleen of all the congenic strains homozygous for H-2z, there were extremely high frequencies of CD5+ B cells. These cells eventually proliferated in an oligoclonal or even monoclonal fashion, and B cell-chronic lymphocytic leukemia (B-CLL) developed in some cases. Because this feature was not observed in H-2d/H-2d homozygotes or H-2d/H-2z heterozygotes, the high CD5+ B cell frequencies are apparently controlled by the homozygosity of a locus or cluster of loci closely linked to H-2z complex of NZW strain. As the CD5+ B cell frequencies in the peritoneal cavity did not differ among the H-2-congenic strains, the frequencies of these cells in the peritoneal cavity and in the spleen appear to be at least in part under separate control. Flow cytometry and Southern blot analyses using an immunoglobulin gene JH probe revealed that the H-2z/H-2z homozygotes, there was a propagation of distinct clonal populations between the spleen and the peritoneal cavity, a finding which suggested that in the major histocompatibility complex (MHC)-related microenvironments for CD5+ B cell propagation differ between the two compartments. All our findings taken together imply that certain different but related MHC haplotypes may predispose either to B-CLL or to autoimmune disease, in close relatives.

The contribution of non-MHC genes to susceptibility to autoimmune diseases

Genetic studies of experimental models of autoimmune diseases, including systemic lupus-like syndromes and organ-specific autoimmunity, provide major information on genetic control of autoimmune diseases. In addition to genes known to be linked to the major histocompatibility complex (MHC), these studies point to multiple genes located outside the MHC that influence the onset and the progression of autoimmune diseases. Identification of these genes and of their interrelationships is now a major task that will be facilitated by recent progress in molecular biology and gene mapping. Among candidate genes, antigen-receptor genes (i.e., immunoglobulin- and T-cell receptor genes) most likely contribute an important part of the autoimmune susceptibility in several of these animal models. Available linkage data suggest a similar involvement of these antigen-receptor genes in several human autoimmune diseases. In addition to a better understanding of pathogenic mechanisms associated with autoimmunity, the knowledge of these disease-predisposing genes is expected to permit a better classification of often complex syndromes as well as the design of new treatments.

The contribution of I-Abm12 to the production of autoantibodies to dsDNA

The development of IgG autoantibodies to dsDNA in NZBxNZW F1 (NZB/W) and NZBxSWR F1 (SNF1) mice have been linked to specific alleles of MHC class II genes contributed by the NZW and SWR parents respectively. Recently, our laboratory has shown that the introduction of the bm12 mutation into NZB mice (NZB.H-2bm12) results in mice which are phenotypically similar to NZB/W F1 mice and, in particular, develop IgG anti-dsDNA antibodies. A variety of immune abnormalities have been described in autoimmune NZB (H-2d) mice. It is, however, unclear at present, whether all these abnormalities are due to the influence or effect of a single set of linked genes or due to multiple genes. It was reasoned that NZB.H-2bm12 mice provide a unique opportunity to examine this issue. Specifically, we bred a series of five different F1 colonies of mice: (a) NZB.H-2bm12/b F1; (b) NZB.H-2bm12/d F1; (c) NZB-H-2b/d F1; (d) NZB-H-2bm12 x B6.C-2bm12 F1 (NZB/B6.H-2bm12 F1); and (e) NZB x B6.C-H-2bm12 F1 (NZB/B6.H-2d/bm12 F1) mice. All groups of mice were serially followed for the appearance of IgM and IgG anti-ssDNA and anti-dsDNA antibodies, splenic CFU-B, spontaneous secretion of IgM, FMF analysis, proteinuria and survival. We report herein that H-2bm12 genes have a dominant influence on the appearance of IgG anti-dsDNA antibodies. In contrast, antibodies to ssDNA, IgM secreting cells, CFU-B and Ly-1 B cells are linked to genes from the NZB background. Finally, we particularly note an absence of IgG antibodies to dsDNA in NZB-H-2b/d F1 mice.