Complete sequence of HLA-B27 cDNA identified through the characterization of structural markers unique to the HLA-A, -B, and -C allelic series

Cutting Edge: HLA-B27 Acquires Many N-Terminal Dibasic Peptides: Coupling Cytosolic Peptide Stability to Antigen Presentation

Ag presentation by MHC class I is a highly inefficient process because cytosolic peptidases destroy most peptides after proteasomal generation. Various mechanisms shape the MHC class I peptidome. We define a new one: intracellular peptide stability. Peptides with two N-terminal basic amino acids are more stable than other peptides. Such peptides should be overrepresented in the peptidome of MHC class I-associated peptides. HLA-B27 binding peptides use anchor residue R at P2 and, although most amino acids are allowed, particular amino acids are overrepresented at P1, including R and K. We show that such N-terminal dibasic peptides are indeed more efficiently presented by HLA-B27. This suggests that HLA-B27 can present peptides from Ags present in fewer copies than required for successful peptide generation for other MHC class I molecules.

Monomorphic HLA class I-(non-A, non-B) expression on Ewing's tumor cell lines, modulation by TNF-alpha and IFN-gamma

In this study, the expression of polymorphic and non-polymorphic MHC antigens in Ewing's tumor (ET) cells was examined by surface staining, Western blots and transcriptional analysis. Cell lines derived from Ewing's tumors largely lack polymorphic HLA class Ia antigens of both the HLA-A and the HLA-B loci but binding of monomorphic HLA antibodies indicates significant expression of HLA-C locus antigens and/or HLA class Ib molecules. HLA Ib molecules encoded by the HLA-E, -F or -G loci with a molecular mass of less than 44 kDa were not detected in lysates of either constitutive or TNF-alpha plus IFN-gamma treated ET cells. Two representative ET cell lines with either detectable HLA-A, -B antigens (A673) or absolutely non-detectable HLA-A, -B antigens (SK-ES-1) were further subjected to transcriptional analysis. A673 mRNA hybridized with HLA-A, -B, -C and HLA-E-specific probes in Northern blots. By contrast, mRNA specific for HLA-A, -B, -C was negative in SK-ES-1 but TNF-alpha plus IFN-gamma reconstituted HLA-A, -B, -C transcription in this cell line. HLA-E was transcribed in A673 but not in SK-ES-1. Combining mRNA and surface expression of HLA class Ia molecules results in a highly variable pattern of defective HLA class I expression in this type of neuroectodermal tumor. The involvement of the ET-specific fusion transcript EWS/Fli-1 in modulating the HLA-A and -B locus antigens is likely to occur by the upregulation of c-myc in these tumors. The exceptionally constant expression of HLA-C or some other non-A, non-B antigens (reactive with defined monoclonal antibodies) implies important consequences on tumor-cell resistance against specific CTL and NK activity in vivo.

Cross-reactivity between an HLA-B27-derived peptide and a retinal autoantigen peptide: a clue to major histocompatibility complex association with autoimmune disease

Statistical correlations between the expression of various HLA antigens and certain autoimmune diseases have been observed for both HLA class I and II antigens. Autoimmune diseases like spondyloarthropathies and anterior uveitis are associated with HLA-B27, but uveitis in Behçet's disease with HLA-B51. We describe a peptide from disease-associated HLA class I antigens sharing sequence homologies with a highly uveitogenic epitope from the retinal autoantigen S-antigen. S-antigen induces autoimmune uveitis in the animal model and is a major autoantigen in human disease. The HLA peptide induced uveitis in the Lewis rat and, moreover, suppressed S-antigen-induced disease when administered orally. Patients' PBL cross-reacted with the HLA- and corresponding retinal peptide, explaining the organ specificity of the disease.

Early events in the assembly of major histocompatibility complex class II heterotrimers from their free subunits

Endogenous antigen presentation by major histocompatibility complex class II molecules can be understood if class II alpha beta heterodimers bind peptide in the endoplasmic reticulum (ER) before they associate with the invariant chain (Ii). We have studied the assembly of class II molecules from the free alpha, beta and Ii subunits to examine the existence of a class II alpha beta heterodimer as an intermediate in the assembly of class II alpha beta Ii heterotrimers in the ER. In human kidney cell transfectants, the free class II alpha and beta subunits and the class II alpha beta heterodimer are retained in the ER by association with the chaperonin immunoglobulin binding protein (BiP) and Ii is retained through its cytoplasmic tail. Co-expression of Ii results in release of BiP from class II alpha beta complexes and exit of class II alpha beta Ii heterotrimers from the ER. We show that the cytoplasmic tail and the transmembrane region of the class II alpha and beta chain is not essential for proper assembly of the class II alpha beta heterodimer. We followed assembly of the class II alpha beta Ii heterotrimers in wild-type cells. The class II subunits assemble post-translationally. No class II alpha beta heterodimers could be isolated as intermediates in the formation of class II alpha beta Ii heterotrimers, suggesting that peptide binding by class II molecules in the ER is necessarily inefficient.

HLA class I non-coding nucleotide sequences, 1992

We present a compilation of the nucleotide sequences of the non-coding regions of the human HLA class I genes which complements previously published information on exon sequences. The listing includes the 5' and 3' untranslated (UT) regions, and introns 1-7. The HLA class I loci and their alleles from which non-coding sequences were derived are listed in Table 1, together with source references. Where possible, locus and allele designations follow the Nomenclature for factors of the HLA system 1991 (Bodmer et al., 1992). In aligning sequences, nucleotides which are conserved between all class I genes are specified only by the consensus sequence, and are indicated by a hyphen (-). To maintain the alignment between different alleles, an asterisk (*) is inserted where there is a gap in the sequence. An unavailable sequence is indicated by a period (.). Regions of sequence too diverse to be accurately compared are represented by an exclamation mark (!). Sequence motifs previously classified as having an important role in HLA class I regulation or processing, such as enhancer sequences, are identified at the bottom of the sequence comparison. It is not our intention in this paper to present an analysis of the many features revealed by this compilation. However, we hope that the information will provide important reference material for studies of HLA class I mRNA processing (Cianetti et al., 1989), promoter regulation (David-Watine et al., 1990) and in the design of allele, locus or region specific PCR primers (Summers et al., 1991). We hope to update this compilation in due course, and we would welcome sequence information not included in this publication, as well as comments and corrections that help to maintain the accuracy of the information.

Ankylosing spondylitis and HLA-B27: restriction fragment length polymorphism and sequencing of an HLA-B27 allele from a patient with ankylosing spondylitis

Two groups of patients with ankylosing spondylitis (AS) from England and Poland were examined for restriction fragment length polymorphisms (RFLPs) associated with the disease. No preferential association was found between the 9.2 kb PvuII fragment in HLA-B27 positive patients with AS compared with HLA-B27 healthy subjects as had been previously reported. In the English group, however, a 14 kb PvuII fragment was more common in HLA-B27 positive subjects with AS than in normal controls. Also 4.6 and 3.7 kb PvuII fragments were more prevalent in subjects without AS than in the group with AS, but these results were confined to the English group. Furthermore, the sequence of an HLA-B*2705 gene isolated from a patient with AS was examined, and no significant differences were found compared with the sequence isolated from a healthy subject. There do not seem to be significant genetic differences in the coding or in the regulatory region in HLA-B27 alleles, in subjects with or without AS.

A nucleoprotein peptide of influenza A virus stimulates assembly of HLA-B27 class I heavy chains and beta 2-microglobulin translated in vitro

Most cytotoxic T lymphocytes (CTL) recognize epitopes of foreign viral proteins in association with class I major histocompatibility complex (MHC) molecules. Viral proteins synthesized in the cytoplasm require intracellular fragmentation and exposure to the class I antigens for the development of CTL responses. Although indirect evidence for binding of peptides to class I antigens has accumulated, direct binding has only been shown recently. The formation of complexes between peptide and class I antigen may occur in the endoplasmic reticulum (ER) and peptides have been shown to induce assembly of the class I complex. We have translated the messenger RNAs encoding HLA-B27 (subtype 2705) and beta 2-microglobulin in a rabbit reticulocyte lysate supplemented with human microsomal membranes (to mimic ER membranes), in the absence and presence of a peptide derived from the nucleoprotein (residues 384-394) of influenza A virus. This peptide induces CTL activity against target cells expressing the HLA-B27 antigen. Here we report direct evidence that the nucleoprotein peptide promotes assembly of the HLA-B27 heavy chain and beta 2-microglobulin, and that this can occur in the ER immediately after synthesis of the two proteins.

Class I major histocompatibility complex cDNA clones from sheep thymus: alternative splicing could make a long cytoplasmic tail

To investigate the class I major histocompatibility complex (MHC) genes expressed in the young sheep thymus, a cDNA library was screened with a human HLA-B7 cDNA probe under conditions of relaxed stringency. Thirteen clones were isolated and found by partial sequences to fall into five classes, requiring the expression of at least three loci. One sequence was found six times, almost half of the total, and may thus represent the major message expressed in the young sheep thymus. One of the clones was found to have failed to excise the intron between cytoplasmic exons 7 and 8, leading to the predicted synthesis of a cytoplasmic domain 23 amino acids longer than the other sheep sequences, and 15 amino acids longer than any cytoplasmic domain previously described. The sequences of all the clones were found to be most similar to bovine, and least similar to mouse class I MHC sequences.

Demonstration of cross-reactivity between bacterial antigens and class I human leukocyte antigens by using monoclonal antibodies to Shigella flexneri

Bacterial envelope proteins which share immunodeterminants with the human leukocyte antigen (HLA) class I histocompatibility antigen HLA-B27 may invoke spondyloarthritic disease through the process of molecular mimicry in patients expressing this phenotype. Monoclonal antibodies generated by the immunization of BALB/c mice with envelope proteins of Shigella flexneri type 2a were tested for reactivity against cultured lymphoblastoid cell lines of defined HLA phenotype. As measured by flow microfluorometry, four immunoglobulin M monoclonal antibodies reacted preferentially with HLA-B27-positive lymphocytes (HOM-2, MM) as compared with a B27-loss mutant line (1065) or cells lacking major histocompatibility complex class I antigen (Daudi, K562). Monoclonal antibodies also reacted with mouse EL-4 cells transfected with and expressing the HLA-B7 gene. Western immunoblot analysis of isolated enterobacterial envelopes demonstrated that the reactive epitope was present on bacterial proteins with an apparent relative molecular mass of 36 and 19 kilodaltons. The structural basis for the cross-reactivity of bacterial antigen and HLA-B27 appeared to reside in the portion of the HLA molecule that is responsible for allotypic specificity (amino acids 63 through 83), since monoclonal antibodies were positive by enzyme-linked immunosorbent assay with synthetic polypeptides corresponding to this segment.

Expression and immunogenicity of HLA-B27 in high-transfection recipient P815: a new method to induce monoclonal antibodies directed against HLA-B27

The immunization of a (BALB/c x C57BL/6) FI mouse with murine transfectants expressing the HLA-B27 antigen resulted in a panel of polymorphic monoclonal antibodies with specificity for HLA-B27 and some additional HLA-antigens. Specificity of the antibodies was defined by cytofluorometric analysis on a panel of lymphoblastoid cell lines (LCL) derived from HLA typed individuals. Three of these antibodies are cytotoxic, and one of them inhibits B27-specific T cell cytotoxicity. Our results indicate that HLA-class I transfectants could be used to generate polymorphic antibodies, and that these antibodies may be helpful for HLA typing and for definition of epitopes recognized by T cells.

Allelic variation in HLA-B and HLA-C sequences and the evolution of the HLA-B alleles

Several new HLA-B (B8, B51, Bw62)- and HLA-C (Cw6, Cw7)-specific genes were isolated either as genomic cosmid or cDNA clones to study the diversity of HLA antigens. The allele specificities were identified by sequence analysis in comparison with published HLA-B and -C sequences, by transfection experiments, and Southern and northern blot analysis using oligonucleotide probes. Comparison of the classical HLA-A, -B, and -C sequences reveals that allele-specific substitutions seem to be rare events. HLA-B51 codes only for one allele-specific residue: arginine at position 81 located on the alpha 1 helix, pointing toward the antigen binding site. HLA-B8 contains an acidic substitution in amino acid position 9 on the first central beta sheet which might affect antigen binding capacity, perhaps in combination with the rare replacement at position 67 (F) on the alpha 1 helix. HLA-B8 shows greatest homology to HLA-Bw42, -Bw41, -B7, and -Bw60 antigens, all of which lack the conserved restriction sites Pst I at position 180 and Sac I at position 131. Both sites associated with amino acid replacements seem to be genetic markers of an evolutionary split of the HLA-B alleles, which is also observed in the leader sequences. HLA-Cw7 shows 98% sequence identity to the JY328 gene. In general, the HLA-C alleles display lower levels of variability in the highly polymorphic regions of the alpha 1 and alpha 2 domains, and have more distinct patterns of locus-specific residues in the transmembrane and cytoplasmic domains. Thus we propose a more recent origin for the HLA-C locus.

Direct analysis of single nucleotide variation in human DNA and RNA using in situ dot hybridization

Using oligonucleotide hybridization, single and multiple nucleotide differences between alleles were detected directly in genomic DNA without electrophoretic separation. The DNA was immobilized in depressions in an agarose gel (in situ dots) and hybridized with radiolabeled, allele-specific oligonucleotide probes. An oligonucleotide complementary to a unique sequence region of the human major histocompatibility complex gene HLA-B27 only hybridized with genomic DNA from an HLA-B27-positive individual. Two other oligonucleotides complementary to the normal human beta-globin gene (beta A) and to the sickle cell globin gene (beta S) were synthesized. Using competition hybridization conditions which included the presence of a 10-fold molar excess of unlabeled oligonucleotide complementary to the other beta-globin allele, DNA from individuals homozygous for the normal beta-globin gene (beta A beta A) hybridized to the beta A probe exclusively, whereas DNA from individuals homozygous for the sickle cell globin gene (beta S beta S) hybridized only with the probe for the sickle cell gene. As expected, DNA from heterozygous individuals bound to both probes. Similar results were obtained with total human RNA immobilized in in situ dots. Possible applications of this methodology include genetic disease diagnosis, population carrier screening, HLA "DNA" typing, and DNA and RNA sequence polymorphism analysis.

The use of fusion proteins to study HLA-B27-specific allorecognition

Potential antigenic regions of the various external domains of the HLA-B27 antigen were expressed as fusion proteins in bacterial hosts and analyzed for their ability to induce humoral and cellular responses. Monoclonal antibodies directed against the proteins recognized monomorphic determinants of denatured HLA-antigens, but not B27-antigens expressed by intact lymphocytes. T-cell proliferation and IL-2 secretion were induced with a fusion protein representing regions of the first and second domains around amino acid residue 114. None of the fusion proteins stimulated cytotoxic T-lymphocytes (CTL) in an HLA-specific manner, although several included those amino acid sequences thought to be important for CTL recognition.

Postdysenteric reactive arthritis. A clinical and immunogenetic study following an outbreak of salmonellosis

Following an outbreak of foodborne gastroenteritis caused by Salmonella typhimurium, questionnaires were sent to affected individuals and then to the family physicians of any who experienced extra-enteric complications. Of 260 individuals infected with S typhimurium for whom adequate data were obtained, 19 patients developed joint disease (7.3%). All were men; the mean age +/- SD was 39.3 +/- 1.6 years. Among the 16 patients for whom this information was available, the interval from the onset of diarrhea to the onset of joint pain was less than 7 days in 7, 8-21 days in 2, and greater than 21 days in 7. There was a significantly longer duration of diarrhea in those patients with joint disease (mean +/- SEM 15.2 +/- 2.6 days) than in those without complications (10.0 +/- 1.1 days) (P less than 0.01). The joint disease was monarticular in 3 patients and polyarticular in 16. The joints most commonly affected were the elbow (47%), wrist (47%), knee (42%), low back (32%), and shoulder (32%). Six of the 19 patients had at least 1 extraarticular feature: ocular (5 patients), mucosal (1 patient), urethral (2 patients), or cutaneous (1 patient). Of these 19 patients, 11 were located and agreed to HLA typing. Four were positive for HLA-B27, 6 were HLA-B7 positive, and 1 had HLA-Bw60. Of the 4 B27 positive patients, 3 were DR1 positive; of the 6 B7 positive patients, 5 were DR2 positive.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and analysis of HLA class I cDNA encoding a new HLA-C specificity Cx52

HLA-C loci frequently have an unclassifiable "blank (CwBL)" specificity. It is unclear whether HLA-C specificities associated with the haplotypes of A24 Bw52 CwBL DR2 DQw1 and Aw33 B44 CwBL DRw13 DQw1 in Japanese (tentatively named Cx52 and Cx44, respectively) really exist. Southern hybridization experiments revealed that restriction enzyme-cleaved genomic DNA from AKIBA, consanguineous HLA homozygote, two other homozygotes with the former haplotype, and three homozygous cells with the latter haplotype hybridized strongly with an HLA-C-specific probe. We have screened the cDNA library constructed from AKIBA to isolate cDNA clones encoding the putative Cx52 antigen, and picked up 103 cDNA clones with HLA-class I DNA probes as possible candidates. By restriction enzyme mapping and Southern hybridization of selected clones, we identified three isotypes of cDNA clones, pA01, pB55, and pC68, which appeared to encode A24, Bw52, and Cx52, respectively. The nucleotide sequence of pC68 showed higher homology with exons of the HLA-C gene than with those of the HLA-A and HLA-B genes, especially in exons 6-8 which include the HLA-C-specific region. Comparison of amino acid sequences showed more than 86% homology among Cw1, Cw2, Cw3, and new pC68-encoded Cx52 proteins. These results support the notion that the inability to define C antigens serologically in this Cx52 haplotype is not due to a HLA-C gene deletion or mutation, but to the absence of typing sera.

Pattern of nucleotide substitution at major histocompatibility complex class I loci reveals overdominant selection

The major histocompatibility complex (MHC) loci are known to be highly polymorphic in humans, mice and certain other mammals, with heterozygosity as high as 80-90% (ref. 1). Four different hypotheses have been proposed to explain this high degree of polymorphism: (1) a high mutation rate, (2) gene conversion or interlocus genetic exchange, (3) over dominant selection and (4) frequency-dependent selection. In an attempt to establish which of these hypotheses is correct, we examined the pattern of nucleotide substitution between polymorphic alleles in the region of the antigen recognition site (ARS) and other regions of human and mouse class I MHC genes. The results indicate that in ARS the rate of nonsynonymous (amino acid altering) substitution is significantly higher than that of synonymous substitution in both humans and mice, whereas in other regions the reverse is true. This observation, together with a theoretical study and other considerations, supports the hypothesis of overdominant selection (heterozygote advantage).

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.

Autoantibodies to HLA B27 in the sera of HLA B27 patients with ankylosing spondylitis and Reiter's syndrome. Molecular mimicry with Klebsiella pneumoniae as potential mechanism of autoimmune disease

Ankylosing spondylitis (AS) and Reiter's syndrome (RS) both show a strong correlation with the HLA B27 haplotype. We studied whether sharing of homologous amino acid sequences in the HLA B27 antigen with an invading microbe might occur, and if so, what is the biological significance of such homology. In a computer search of the Dayhoff data bank, we found a homology of six consecutive amino acids between HLA B27.1 antigen residues 72-77 and Klebsiella pneumoniae nitrogenase residues 188-193. These shared sequences are hydrophilic, suggesting locations on molecules exposed to the cell surface. Immunochemical analysis showed that 18 of 34 sera from patients with RS (53%) and 7 of 24 sera from patients with AS (29%) contained antibodies that bound to a synthesized peptide sequence representing residues 69-84 of HLA B27.1. In contrast, only 1 of 22 sera from healthy, B27+ controls (5%) contained antibodies to this peptide (p less than 0.01). Sera from three HLA B27- patients with RS did not possess antibodies to the HLA B27 peptide. Additionally, greater than 40% of HLA B27 patients with AS or RS had antibodies to Klebsiella residues 184-193, while none of the normal nonarthritic HLA B27 haplotype subjects did. Our results suggest that an autoimmune response(s) directed against HLA B27.1 may be a pathogenic mechanism in a subset of patients with AS and RS. Further, this response may initially be induced against Klebsiella pneumoniae, a microorganism that shares sequence homology with HLA B27.

Structure, expression, and molecular mapping of a divergent member of the class I HLA gene family

A class I gene distinct from HLA-A, -B, or -C was identified in a cosmid clone and transfected into mouse L cells. The gene, placed adjacent to the polyoma enhancer, produced a full-length class I mRNA and high levels of a 43-kDa protein in the cytoplasm. The surface expression of the gene product required its association with human beta 2-microglobulin. The protein was recognized by a xenoantiserum raised against a mixture of human B- and T-cell lines. The product was also serologically reactive with the HLA framework monoclonal antibodies. The complete nucleotide sequence of the gene was determined and a specific oligonucleotide probe was synthesized. This probe was used to identify a full-length mRNA transcript in a B-lymphoblastoid cell line (JY). The gene was mapped within a 190-kilobase Not I restriction fragment located in the telomeric portion of the human major histocompatibility complex. Distinct features of the gene include the structure of the promoter, the position of the translation initiation site, a frameshift mutation at the carboxyl terminus, the insertion of an Alu repeat element in the eighth exon, divergence in the derived amino acid sequence, and the lack of expression of the gene in some cells.

Isolation, expression, and the primary structure of HLA-Cw1 and HLA-Cw2 genes: evolutionary aspects

The HLA-Cw1 and -Cw2 genes were identified in a genomic library and their products characterized by biochemical methods. The HLA-Cw1 and -Cw2 genes, upon transfection in mouse L cells, give rise to class I antigen heavy chains that associate with neither mouse nor human beta-2 microglobulin. They are indistinguishable in isoelectric point from polypeptides identified as HLA-Cw1 and -Cw2 in human cells. The nucleotide sequence of HLA-Cw1 and -Cw2 and their comparison with HLA-Cw3, the only other known HLA-C sequence, reveal a characteristic pattern of locus-specific amino acids. A comparison of 13 different human class I primary structures leads us to speculate that the most variable region in HLA class I antigens, positions 61-83, could assume an alpha helical structure of critical importance for class I antigen function. The locus specificity and the higher degree of intralocus conservation in the COOH-terminal region, especially in the transmembrane and cytoplasmic domains, must reflect evolutionary ancestry rather than positive selection. In view of the pattern and types of substitutions observed for HLA-C locus products, their function as immune response gene products is questioned.

Distribution of HLA-B27 subtypes in patients with ankylosing spondylitis: the disease is associated with a common determinant of the various B27 molecules

HLA-B27 subtypes can be defined by cellular, serological, and biochemical techniques. The seven subtypes so far identified represent structural variants of B27 with limited variations in the amino acid sequence of the B27 molecule. The routinely typed B27 'antigen' remains a common (shared, public) determinant present on various B27 molecules. The distribution of the subtypes varies strongly among different ethnic groups and they occur in different linkage disequilibria. In the healthy Dutch population only two subtypes were found: B27W (B27 X 1, B27M2+) (90%) and B27K (B27 X 2, B27M2-) (10%). A similar distribution of B27 subtypes was observed in 91 unrelated Dutch patients with ankylosing spondylitis (AS)--namely, 92% B27W and 8% B27K. In Oriental populations the subtype distribution is quite different: B27W occurs in less than 50%, whereas more than 50% individuals are of the B27C and B27D subtypes. Preliminary data indicate that the distribution of subtypes in healthy and diseased Oriental individuals is similar. These results suggest that the B27 and disease (AS) association is not correlated with the structural variations of one of the B27 subtypes, but with a common B27 determinant shared by various B27 subtypes. Consequently, the disease is older than the B27 variants. Further studies on disease and subtype distribution in various ethnic groups might contribute to a better understanding of the origin of both.

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

Genomic DNA from 46 B27+ ankylosing spondylitis, Reiter's syndrome, or normal individuals was digested with Taq I and probed, in Southern blots, with the HLA-B locus specific probe, EI7. Four restriction fragment length polymorphisms (RFLP), 2.5, 3.4, 3.8 and 4.0 or 8.0 kb, were observed for the B27 gene. In Caucasians, one of the B27 variants (2.5 kb) was more frequent in normals and almost never appeared in patients, suggesting a trend that is not yet statistically significant. In the course of defining the B27 polymorphisms, three and two RFLP, respectively, were also found for the B18 and B44 genes.

Immunogenetics

The 1985 Catalog of Mapped Genes (Human Gene Mapping 8; 33) has been used to pick out the known, immunologically important genes; these are then discussed in the following order: genes controlling organs, tissues and cells of the immune apparatus, genes determining 'self' structures, genes determining the structures of immunological specificity, genes determining substances with immunoregulatory and effector properties. The symbols for the genes and the biological functions of their products are explained. The genetics of the ABO blood groups, of the HLA-system and of antibody formation are given in rather more detail.