H. Donner

Development of Insulin-Dependent Diabetes Mellitus Does Not Depend on Specific Expression of the Human Endogenous Retrovirus HERV-K

Conrad et al. stated that the sequence of the truncated IDDMK1,222 env gene encoded a superantigen. Sequence comparison with a variety of additional HTDV/HERV-K env sequences revealed extensive homologies with only a few nucleic acid substitutions. The superantigen sequences encoded by mouse mammary tumor virus (MMTV) also differ between virus strains, in particular within the COOH-terminal residues that may contribute to their Vβ specificity.As the IDDMK1,222 expression clone was not available to test for superantigen function, we amplified and cloned an HTDV/HERV-K sequence using a 5′ primer corresponding to the IDDMK1,222 superantigen sequence and the 3′ primer R-poly(A) described by Conrad et al. As the 3′ R-poly(A) primer was not RNA specific, we used genomic DNA as the template. The Env sequence obtained differed from IDDMK1,222 by six amino acids. One exchange abrogated the premature Env termination signal leading to a longer putative superantigen protein; the other changes were G46→V, H48→R, T115→P, G123→E, and V140→A. Preliminary attempts to use the THP1 cell line for expression of the Env protein failed due to insufficient transfection efficiency (less than 1% transfectants with a reporter gene using different transfection methods). We therefore used a well-established murine system (Gunzburg et al. 1993xGunzburg, W.H., Heinemann, F., Wintersberger, S., Miethke, T., Wagner, H., Erfle, V., and Salmons, B. Nature. 1993; 364: 154–158Crossref | PubMed | Scopus (27)See all ReferencesGunzburg et al. 1993) that allows for higher transfection efficiencies (30%–40% using electroporation). There is as yet no evidence that superantigens are species specific and, indeed, Conrad et al. recently reported similar results using human and murine test systems (Symposium on “Retroviruses and Autoimmunity,” 1998, London). However, murine A20 cells transiently transfected with the IDDMK1,222-related expression clone did not stimulate corresponding BALB/c T cells in a Vβ-specific fashion while A20 cells transfected with an MMTV superantigen induced a Vβ14-selective expansion of T cells. Truncating the longer Env sequence to the size of IDDMK1,222 did not alter the negative result.Clearly, further studies including more HTDV/HERV-K sequences as well as the expression clone established by Conrad et al. are needed to either confirm or refute the hypothesis that a superantigen is encoded by this HERV family. If the superantigen exists, its involvement in the onset or progression of insulin-dependent diabetes mellitus needs to be examined. With regard to other bacterial and especially viral superantigens, it seems very unlikely that the sequence published by Conrad et al. would be unique amongst all HTDV/HERV-K proviruses in encoding a superantigen.

An endogenous retroviral long terminal repeat at the HLA-DQB1 gene locus confers susceptibility to rheumatoid arthritis

Human endogenous retrovirus (HERV) long terminal repeat (LTR) elements contain regulatory sequences that can influence the expression of adjacent cellular genes, which may contribute to breakdowns of the immune function leading to autoimmune disease. Rheumatoid arthritis (RA) is associated with particular HLA-DR/DQ haplotypes that modulate the pathogenesis of this autoimmune disease. We have therefore studied a solitary LTR element (DQ-LTR3) of the HERV-K family at the HLA-DQB1 locus for a possible disease association among 228 RA patients and 311 unrelated blood donors. The DQ-LTR3 was significantly more frequent among patients (76% vs 33%, OR = 5.07,p < 0.0001), with the majority of patients being heterozygous for the DQ-LTR3 (61% vs 22%, p < 0.0001). HLA-DRB1*04 positive patients did still differ for the presence of the DQ-LTR3 (88% vs 70%, OR = 3.03, p < 0.001), with an increase of both DQ-LTR3 homozygous and heterozygous patients, when compared to DRB1*04 positive controls (p = 0.0015). HLA-DR/DQ genotype analysis among HLA-DRB1*04 positive individuals revealed significantly more DQ-LTR3 homozygotes among HLA-DRB1*04-DQBI*03 homozygous patients (72% vs 27%, P = 0.015), and the number of DQ-LTR3 homozygous (23% vs 19%) and heterozygous (66% vs 53%) individuals was also increased among HLA-DRB1*04 heterozygous patients (p = 0.034). The presence of the DQ-LTR3 element increased both the relative risk and the positive predictive value for either DRB1*04-DQB1*03 positive/negative individuals when compared to the presence of HLA-DRB1*04-DQB1*03 alone. In conclusion, these data suggest that this DQ-LTR3 enhances susceptibility to RA.

POLYMORPHISMS OF TAP1 AND TAP2 GENES IN GERMAN PATIENTS WITH TYPE 1 DIABETES MELLITUS

Type 1 diabetes mellitus (IDDM) is an autoimmune disorder in which the alleles HLA DQA1*0501-DQB1*0201 and DQA1*0301-DQB1*0302 confer strong susceptibility. The genes for transporters associated with antigen processing (TAP1 and TAP2) are located near HLA DQ and display only a limited degree of polymorphism. Since polymorphisms of TAP might influence susceptibility to IDDM possibly by selection of different antigen peptides, we investigated sequence variants of TAP1 and TAP2 genes in 120 German patients with IDDM and 218 random healthy German controls by polymerase chain reaction (PCR) followed by sequence-specific oligonucleotide analysis (SSO), single-strand conformation polymorphism (SSCP) analysis and amplification refractory mutation system (ARMS). TAP1*02011 (16% vs. 4% in controls, P = 0.001, RR = 5.0) and TAP2*0101 (96% vs. 69% in controls, P < 0.0001, RR = 10.6) showed a positive association with IDDM. However, these associations disappeared when patients and controls were matched for predisposing HLA DQA1 or DQB1 alleles as well as for DRB1*0401. In conclusion, our findings indicate that the observed association of TAP variants with IDDM in German patients is due to linkage disequilibrium with HLA DQ alleles/DRB1*04 subtypes.