New polymorphisms of HLA-B27 and other B locus antigens detected by RFLP using a locus-specific probe

Rapid screening for HLA-B27 by a TaqMan-PCR assay using sequence-specific primers and a minor groove binder probe, a novel type of TaqMan trade mark probe

HLA-B27 is strongly associated with ankylosing spondylitis (AS). As typing for HLA-B27 is routinely performed by serological methods, false-positive results can be generated. Therefore, several more accurate molecular methods have been developed for HLA-B27 genotyping. We describe a real-time PCR method for the detection of the HLA-B27 allele using sequence-specific primers (SSP) combined with a fluorogenic MGB probe (minor groove binder probe), a novel type of TaqMan probe. The MGB increases the melting temperature (T(m)) of the probe, allowing the use of shorter probes. Moreover, the use of a non-fluorescent quencher (NFQ) attached to the MGB probe improves the efficiency of fluorescence quenching, thus providing a very low fluorescent background. We tested this method on 150 subjects (41 HLA-B27 positive and 109 HLA-B27 negative) who underwent routine HLA-B27 serological testing by flow cytometry (FC). Serology and our TaqMan assay gave identical results in all cases and no false positive or negative results were observed. A graphical representation of fluorescence and normalized reporter signal (DeltaRn) values demonstrated that HLA-B27 positive and HLA-B27 negative samples formed two tight clusters making it possible to clearly differentiate between HLA-B27 positive and negative samples. This single tube PCR method for the detection of HLA-B27 should be particularly suitable for the routine analysis of large numbers of samples in the laboratory.

B*27 in molecular diagnostics: impact of new alleles and polymorphism outside exons 2 and 3

HLA-B*27 is known to be associated with ankylosing spondylitis and several methods have been applied to determine its presence or absence. In this report two molecular methods were used for detection of B*27. The polymerase chain reaction sequence-specific primer (PCR-SSP) method was performed to detect the presence or absence of B*27, whereas the sequence-based typing method (SBT) was used to identify the B*27 subtype. The PCR-SSP method used to detect B*27 was updated to enable the detection of all B*27 alleles. The typing results obtained by this method were compared with the serological typings of 262 individuals. Fifty of them were found to be B*27 positive by PCR-SSP and 46 also showed positive serological reactions with B27-specific sera. The four discrepancies were the result of the presence of B*2712 in three individuals and B*2715 in one individual; both alleles showed no serological reactions with B27-specific antisera. With SBT the sequences of exons 1 through 4 were determined to unequivocally assign the B*27 alleles. Eleven different subtypes were detected in 78 individuals, including three new B*27 alleles: B*27054, B*2715 and B*2717. The allele B*27054 showed an allelic drop out when exon 3 was amplified. Three differences with B*27052 were demonstrated; one in exon 1, one in intron 1 and one in intron 2, the latter being responsible for the allelic drop out. The B*2715 allele was serologically not detectable with several B27-specific sera, but showed Bw4-positive reactions. The sequence of B*2715 showed two mismatches with B*2704. The sequence of B*2717 showed one mismatch with B*27052 at position 248 (A-->T), which was considered to be a conserved position in all B alleles.

HLA-B27 determination using serological methods. A comparison of enzyme immunoassay and a microlymphocytotoxic test with flow cytometry and a molecular biological assay

Typing for HLA-B27 is routinely performed in patients with seronegative spondarthritides. Besides the microlymphocytotoxic test (MLCT), other serological techniques have been developed such as enzyme immunoassays (EIA) using serum or plasma as a source for the determination of soluble HLA-B27 (sHLA-B27) and flow cytometric (FC) methods. The aim of the present study was to check the accuracy and reliability of the EIA for sHLA-B27 in comparison to the MLCT using antibodies against HLA-B27 and cross-reacting specificities (CRS), as well as an FC method and a molecular biological method. Any discrepant results should be typed with the MLCT using a complete panel of anti-HLA-class I antibodies, with FC and with a molecular biological technique. The EIA should also be repeated in those patients, using serum and plasma from a new venipuncture. In 81 patients with rheumatic disorders, the EIA and the MLCT using antibodies against HLA-B27 and CRS were performed. Based on the MLCT with a complete panel of anti-HLA-class I antibodies as a standard, discrepant test results were obtained for 9 out of 81 patients with the MLCT using antibodies against HLA-B27 and CRS and with the EIA. The following wrong results occurred: in the MLCT with anti-HLA-B27 and CRS, there were two false-negative results; in the EIA there were four false-negative and one false-positive results; one sample was undeterminable. In comparison with the MLCT, including the complete panel of HLA-class I antibodies, as well as with a molecular biological technique, typing with FC showed a complete concordance. Our investigations demonstrated that for routine typing for HLA-B27 the MLCT cannot be replaced by EIA because of a significant number of mistypings. The MLCT performed only with antibodies against HLA-B27 and CRS may also lead to typing errors. No errors were detected using flow cytometry. If only serological methods can be performed in a laboratory a combination of flow cytometry and MLCT could therefore enhance the safety of HLA-B27 typing.

Subtypes of HLA-A1 defined on the basis of CTL precursor frequencies

Recently we have shown that limiting dilution analysis can be used to detect cytotoxic T-cell precursor frequencies directed against individual HLA class I antigens. Using the same protocol, we have been able to define two subtypes of HLA-A1, which are indistinguishable by conventional typing sera as well as by cell-mediated lympholysis. One-dimensional isoelectric focusing analysis of the variants did not show any overall charge differences. However, family studies indicated that these HLA-A1 subtypes are genetically determined and can be distinguished on the bases of T-cell precursor frequencies in HLA-A1-negative blood donors.

Restriction fragment length polymorphism analysis in ankylosing spondylitis

We utilized the technique of restriction fragment length polymorphism (RFLP) analysis in order to examine class I major histocompatibility complex genes in 52 Alabama ankylosing spondylitis patients and 107 local control subjects. A 9.2-kilobase PvuII RFLP was identified using the class I-specific B7 cDNA probe pDP001 that was closely associated with ankylosing spondylitis, most specifically with peripheral joint (including shoulder and hip) involvement. This fragment is associated with human leukocyte antigen A3 and A9 alleles, and segregation analysis in 11 multiplex families showed the RFLP to frequently segregate independently of B27 haplotypes. Two more recent studies have not confirmed the association of the 9.2-kilobase PvuII RFLP with ankylosing spondylitis per se, believed to be due to clinical and possibly genetic differences between the patient groups studied. These data strongly suggest at least one other major histocompatibility complex class I gene to be operative in predisposition to or modification of ankylosing spondylitis.

DNA polymorphism of the HLA-B35 gene associated to different HLA-C locus alleles

Peripheral blood leukocyte DNA from 31 donors, previously typed as HLA-B35, was digested with EcoRV and analyzed by Southern transfer and hybridization to an HLA class I probe. Out of 31 HLA-B35 positive (+) individuals, 24 showed a 4.6-kb band, previously associated with the B35 allele by Cohen et al. (Proc Natl Acad Sci USA 80:6289-6292). The HLA-B35 allele has a strong linkage disequilibrium (70%) with the Cw4 allele. All samples having the 4.6-kb band corresponded to HLA-B35+, Cw4+ cells, whereas those lacking the band came from HLA-B35+, Cw4-negative (-) cells. Five HLA-B35-, Cw4+ samples were also studied and none showed the band. An HLA-B locus-specific probe gave a strong hybridization signal to this fragment, whereas an HLA-C locus-specific probe revealed different bands. The results suggest that the 4.6-kb fragment contains the B35 gene. Digestion with other restriction enzymes, located the polymorphic site to the 3' end of the gene. Analysis of 18 additional individuals with other specificities of the "4c" antigenic cluster (HLA-B18, B51, B52 and B53) showed that the EcoRV/4.6 kb-band was also present in 5/5 B52 cells and 4/4 B53 samples.

Four cytotoxic human-human hybridoma antibodies that react with HLA-B27

PBMC were isolated from a multiparous woman with HLA-B27 specific Abs in her serum. The HLA type of the donor was A2,9:B7. The PBMC were EBV transformed, and four cell lines making cytotoxic Abs to HLA-B27+ cells prepared. Hybridomas were constructed by fusing the EBV lines with the human fusion partner KR4. All four mAbs were of IgM isotype. One mAb (TrBH12) reacted specifically with B27+, B37+ and Bw47+ lymphoblastoid cell lines and with all B27+ PBMC except for a rare variant so far found only in one Norwegian family. Another mAb (Tr3B6) was cytotoxic for all B27+ cells tested, including the TrBH12- variant; in addition, it showed weaker cross-reactions to Bw42, B49 and a cell line with the probable phenotype B7,38. Supernatant from the Tr3B6 hybridoma was tested in lymphocytotoxicity against a panel of 658 individuals, 141 of whom were B27+. With this panel, Tr3B6 showed perfect correlation with HLA-B27. The two last mAbs (TrCG10 and TrBF1) reacted with all B27+ cells tested, but in addition showed quite extensive cross-reactions.

Use of RecA protein to enrich for homologous genes in a genomic library

RecA protein-coated probe has been utilized to enrich genomic digests for desired genes in order to facilitate cloning from genomic libraries. Using a previously cloned HLA-B27 gene as the recA-coated enrichment probe, we obtained a mean 108x increase in the ratio of specific to nonspecific plaques in lambda libraries screened for B27 variant alleles of estimated 99% homology to the probe. Class I genes of lesser homology were less enriched: 6.7x for non-B27 genes of estimated greater than 95% homology and 3.7x for other-Class I genes of greater than 80% homology. Loss of genomic DNA during the enrichment procedure can, however, restrict application of this technique whenever starting genomic DNA is very limited. Nevertheless, the impressive reduction in cloning effort and material makes recA enrichment a useful new tool for cloning homologous genes from genomic DNA.

Different linkage disequilibria of HLA-B27 subtypes and HLA-C locus alleles

Subtypes of HLA-B27 have been identified by cellular, serological and biochemical techniques. Comparison of the various B27 subtype designations showed the existence of seven B27 subtypes. The new WHO nomenclature (1987) of the B27 subtypes is included. We further report on different linkage disequilibria (ld) of the B27 subtypes. In Caucasoids, the prevalent subtype B27.5 is in ld with Cw1 and Cw2, whereas B27.2 is linked only with Cw2. In Orientals, the most frequent subtypes B27.4 and B27.6 usually occur with Cw3 or Cw blank; B27.5 mostly occurs with Cw2, and B27.2 is almost absent.