Identification of several functional subgroups of HLA-B27 by restriction of the activity of antiviral T killer lymphocytes

Asymptomatic deficiency in the peptide transporter associated to antigen processing (TAP)

Human HLA class I deficiency is a rare disease which, in most of the patients described to date, results from a defect in subunit 1 or 2 of the peptide transporter associated with antigen processing (TAP). The clinical features of TAP deficiency include a chronic inflammation of the respiratory tract and/or granulomatous skin lesions. In this report, we describe two adult siblings with an HLA class I deficiency. One individual had only spontaneously-healing skin granulomatous lesions, while the second did not display any of the symptoms associated with HLA class I deficiency and could be considered to be healthy. We show that the patients display a homozygous TAP2 mutation which blocks the maturation of HLA class I molecules. Cell surface expression of these molecules is strongly reduced, but three times higher than on cells from other previously described TAP-deficient individuals. This higher expression results, at least in part, from the presence of HLA-B7 molecules which are probably empty of peptide. The numbers of CD8+ alphabeta T cells are almost normal in these patients. The anti-EBV T-cell response of one patient is mediated by HLA-B7 restricted CD8+ alphabeta T lymphocytes recognizing the BMRF1 nuclear EBV antigen, demonstrating that CD8+ alphabeta T cells can participate in anti-viral responses. This study shows that TAP deficiency can remain totally asymptomatic for several decades, and suggests that in some cases, TAP-independent immune responses provide efficient protection from most of the common intracellular pathogens.

Differences in peptide presentation between B27 subtypes: the importance of the P1 side chain in maintaining high affinity peptide binding to B*2703

Susceptibility to spondyloarthropathies is strongly associated with the MHC class I molecule HLA-B27, and is hypothesized to result from the presentation of arthritogenic peptides. Subtypes of B27 that differ structurally but are disease-associated ought to be capable of presenting such peptides, while nondisease-associated subtypes would not. We demonstrate that B*2703, the predominant West African B27 subtype that may not predispose to disease, is not recognized by most B*2705-alloreactive CTL, and does not efficiently present a known B*2705-restricted influenza A nucleoprotein (NP) peptide. We show inefficient presentation is due to a reduced binding affinity of B*2703 for the NP peptide. Furthermore, substituting Arg for the naturally occurring Ser at P1 of the NP peptide, restores high affinity binding and efficient presentation by B*2703. Our results suggest that B*2703 will bind and present efficiently only a subset of the peptides that bind to B*2705, in particular those with Arg or Lys at P1. The apparent lack of disease in individuals with B*2703 may be due to an inability to bind and present putative arthritogenic peptides.

T cell allorecognition and endogenous HLA-B27-bound peptides in a cell line with defective HLA-B27-restricted antigen presentation

The B*2702+ lymphoblastoid cell line NW is unable to present at least some HLA-B27-restricted viral antigens to T cells. This defect was genetically inherited, and was suggested to be related to the nature of the HLA-B27 binding peptides reaching the endoplasmic reticulum in these cells (Pazmany et al., J. Exp. Med. 1992. 175: 361). In the present study 17 of 19 HLA-B27-specific alloreactive cytotoxic T lymphocyte clones recognizing the B*2702 subtype on other cells also lysed NW cells. Only two cytotoxic T lymphocyte clones failed to lyse NW while efficiently killing other B*2702+ cell lines. The high-performance liquid chromatography profiles of the B*2702+ bound peptides extracted from NW cells was similar, but not identical, to those from two other cell lines. These results indicate that the HLA-B27-bound peptide repertoire in NW cells is not fundamentally different from those in other B*2702+ cells. Our data argue against gross differences in peptide processing or transport as being responsible for the defective presentation of particular HLA-B27-restricted viral antigens to T cells, but do not rule out distinct presentation of some endogenous peptides. Differences in the capacity to present certain peptides could cause differential susceptibility among HLA-B27+ individuals to ankylosing spondylitis.

Different HLA-B27 subtypes present the same immunodominant Epstein-Barr virus peptide

An immunological basis has been postulated for the strong association between at least five subtypes of the HLA-B27 allele (B27.01, .02, .04, .05, and .06) and ankylosing spondylitis, namely that cytotoxic T lymphocyte (CTL) responses are induced against an "arthritogenic" peptide that these different subtypes can all present. This requires a degree of overlap between the peptide binding repertoires of different B27 molecules. The present work, using CTL responses to Epstein-Barr virus (EBV) as a model system in which to identify B27-restricted epitopes, provides the first direct evidence that different disease-related alleles can present the same immunodominant peptide. We first noted that EBV-specific CTL clones, whether from B27.05-, B27.02-, or B27.04-positive donors, were largely subtype-specific in their restriction, recognizing only EBV-transformed B cell lines of the relevant B27 subtype. However, when tested against targets expressing individual EBV proteins from recombinant vaccinia virus vectors, all B27.05-restricted, all B27.02-restricted, and a proportion of B27.04-restricted clones were reactive to the same viral nuclear antigen, Epstein-Barr nuclear antigen (EBNA)3C. In subsequent peptide sensitization assays, all the EBNA3C-specific clones tested and also the EBNA3C-specific component within polyclonal CTL preparations from B27.05-, B27.02-, or B27.04-positive donors recognized the same immunodominant viral peptide RRIYDLIEL (EBNA3C residues 258-266). This sequence accords well with the proposed B27.05 peptide motif and clearly must be accommodated within the different peptide binding grooves of B27.05, B27.02, and B27.04 molecules. Clonal analysis revealed a second component of the B27.04-restricted response that was not shared with other subtypes. This was directed against an EBV latent membrane protein LMP2 epitope whose sequence RRRWRRLTV satisfies some but not all requirements of the B27.05 peptide motif. We conclude that there is indeed a degree of functional overlap between different B27 subtypes in their selection and presentation of CTL epitopes.

In vitro human cytotoxic T cell responses against influenza A virus can be induced and selected by synthetic peptides

Studies on human anti-influenza cytolytic activities have demonstrated that cytotoxic T lymphocytes (CTL) from HLA-B37 individuals react preferentially with the peptide corresponding to residues 335-349 of the nucleoprotein, whereas CTL from HLA-A2 donors recognize peptide 57-68 from the viral matrix as a dominant epitope. We studied the secondary CTL response, obtained from peripheral blood mononuclear cells, of an HLA-A2+,B37+ individual stimulated either by infectious virus or by synthetic peptides. Only an HLA-B37-restricted response was detected after stimulation by the whole virus, showing an immunodominance of this activity over that restricted by HLA-A2. Moreover, human cytotoxic cell lines were successfully obtained after stimulation of peripheral blood mononuclear cells with synthetic peptides. Under these conditions, it was possible to selectively reveal the existence of an HLA-A2-restricted activity directed against the matrix peptide. These results demonstrate that, at least in vitro, it is possible to stimulate a latent repertoire by using synthetic peptides. Nevertheless, we could not induce a response against the matrix or the nucleoprotein peptides in HLA-A2- or B37- individuals, suggesting that a finer selection of synthetic peptides would be necessary for their possible utilization to induce CTL during vaccination.

Epitope mapping of an HLA-B27 monoclonal antibody that also reacts with a 35-kD bacterial outer-membrane protein

Ye-3 is an HLA-B27-specific murine monoclonal antibody recognizing the heat-modifiable protein of Enterobacteriaceae. Here we used recombinant hybrid molecules between the HLA-B7 and HLA-B27 antigens to delineate the epitope recognized by Ye-3. Results of these experiments indicated that the segment of HLA-B*2705 spanning residues 77-81 was critical to the reactive epitope. It is known to be a major serological and functional recognition site of HLA-B*2705 and our data give support for its involvement also in the serological cross-reactivity with bacterial antigens.

Dysfunction of HLA-B27

Every HLA antigen, as defined by the WHO-HLA Nomenclature, is unique. The major function of these molecules is to present antigen-peptides to the T-cell receptor, thereby contributing to the immunological defence mechanism. This function is regulated for each MHC antigen by its unique structure, with the peptide-binding pockets of the three-dimensional groove of the corresponding molecules playing the critical role. However, HLA-B27 is special by virtue of its disease association(s). Various aspects which might provide an explanation for--or at least a clue to an understanding of the specific role of--B27 in its disease associations are reviewed. Since it appears that there are no published experimental data which would support either of the alternative hypothetical possibilities, the bulk of current theories must therefore be purely speculative. The only lead to a better understanding of the function of B27 in disease associations is the postinfectious reactive arthritis. If it is the B27 molecule itself which is involved, further in vivo work on B27 transgenic animals might help solve this problem with its numerous unknown factors.

Acute anterior uveitis and HLA-B27

All studies among acute anterior uveitis patients (AAU) agree on the importance of and high association with HLA-B27. However, the majority of the HLA-B27+ population will never develop AAU. The partial association of AAU and HLA-B27 is probably not based on a preferential association with a particular B27 subtype, since the HLA-B27 subtypes are equally distributed among normal controls and AAU patients. Therefore, other factors increase the susceptibility to HLA-B27 associated diseases. Family investigations among the relatives of AAU and AS patients suggest the existence of other pathogenic genetic factors in addition to HLA-B27. Due to extensive research, associations with other genes on chromosome 6 could almost be excluded and associations with genes on other chromosomes were not yet found. The only reproducible association between AAU and any genes or gene products is, at the moment, still the association with HLA-B27. However, its role, which most probably is functional, is far from clear.

HLA-B27 and HLA-A2 subtypes: structure, evolution and function

Beyond the resolution of tissue typing serology, HLA class I antigens display a certain level of structural microheterogeneity, that allows their subdivision into subtypes. The structure of these subtypes shows that multiple mechanisms operate in the generation of HLA polymorphism and suggests possible evolutionary pathways for subtype diversification. In addition, subtype polymorphism critically affects cellular allorecognition and antigen presentation to self-restricted T cells. These properties are used to define the structure and diversity of T-cell epitopes. In this review, José López de Castro discusses the nature and evolution of this polymorphism and its modulation of antigen recognition by cytolytic T lymphocytes.

Role of different lymphocyte subsets in human anti-viral T cell cultures

We have systematically studied uncloned human cell lines derived from anti-influenza A virus or anti-Epstein-Barr virus (EBV) bulk cultures, or from cultures highly enriched for CD4+ or CD8+ lymphocytes. The most noteworthy results are the following: (1) Anti-viral bulk cultures consisted of more than 90% of CD8+ cells in all cases. In contrast, anti-HLA cell lines are composed of approximately 50% CD8+ and 50% CD4+ cells. All of the CD8+ and CD4+ cells present in the culture were also 4B4+/2H4-. (2) In anti-viral bulk cultures, the cytolytic activity was restricted by HLA class I molecules and almost exclusively through a single HLA class I molecule. (3) Positively or negatively selected CD8+ lines showed the same restriction pattern. They grew less efficiently than bulk cultures but could be maintained in the absence of CD4+ cells. The CD4+ cells were however necessary at the beginning of the culture for the development of cytolytic anti-influenza virus CD8+ cells, whereas they were not required for the development of cytolytic anti-EBV CD8+ cells. (4) The CD4+ cell lines grew more actively than bulk cultures. A cytolytic activity for virus-infected cells was constantly detected in these culture from the third passage onward and it was always restricted by HLA class II molecules. This activity was maintained throughout the culture period. However, class II-restricted cytolytic cells were not detected during primary or secondary responses in vitro.

Modulation on immunogenicity by HLA-B27 subtype polymorphism

Cells from the same HLA-B27- individual, PA, were stimulated in vitro in primary mixed lymphocyte culture, with either B*2705+ or B*2704+ lymphoblastoid cell lines, in independent experiments. Cytolytic T lymphocytes (CTL) were cloned at limiting dilution and the clones obtained were screened for anti-B27 alloreactivity. Most of the CTL clones generated against the B*2705+ stimulator cells were directed against the B*2705 antigen. In contrast, no anti-B27 CTL clones were found among those derived against the B*2704+ stimulator cells. This was not due to a poor cytotoxic response against these cells because a large proportion of the T cell clones derived from this stimulation were cytotoxic. B2704 differs from B*2705 by only two amino acid changes at positions 77 and 152. Previous studies (Aparacio, P. et al., Eur. J. Immunol. 1988.18: 203) have shown that none of the anti-B*2705 CTL clones derived from donor PA and amenable to detailed characterization cross-reacted with B*2704, suggesting that most of this cytotoxic response was directed against an immunodominant determinant contributed for by residues 77 and/or 152 from B*2705. The present results further suggest that the changes at these positions in B*2704 alter this determinant in such a way that B*2704 becomes less immunogenic for the particular individual PA. Furthermore, a similar poor anti-B*2704 CTL response was obtained from a second B27- responder individual, AE, stimulated with another B2704+ cell line. The single anti-B*2704 CTL clone, 64.8P, isolated from this second individual, displayed an unusual reaction pattern in that it cross-reacted with all B27 subtypes with changes only at or close to positions 77 and 152, including B*2705. Significantly, the only HLA-B27 subtype that was not recognized by CTL 64.8P was B*2703, which differs from B*2705 only at residue 59. This residue is located in the three-dimensional structure at the opposite end from residues 77 and 152 at the surface of the antigen-binding groove of the class I molecule. Thus, the area around residues 77 and 152 is not an essential part of the epitope recognized by CTL 64.8P.

Genetics of the spondarthropathies

Recent investigation of the possible role of bacteria in the pathogenesis of AS has provided very interesting data. What is at present lacking is a clear demonstration that the findings point to the actual mechanisms involved in the initiation of the disorder. Rapid progress in three related areas of research gives hope that, in the relatively near future, the genetic basis for susceptibility to AS will be elucidated. These are the demonstration of the detailed structure of an HLA class I molecule, of the primary amino acid structure of B27 heavy chain with its subtypes, and of the nature of the interaction between foreign proteins and MHC molecules which leads to antibody and cytotoxic cell responses. It is just possible that the B27 molecules have a disease-promoting capability because of some structural characteristic independent of their antigen binding site. However, it may perhaps be considered more likely that it is the propensity of the specific antigen-binding site itself to bind to a particular group of antigenic peptides that will explain the susceptibility of B27-positive individuals to several clinical disorders. The ability to study the properties of antigenic epitopes which preferentially bind to the very variable binding site of different MHC molecules raises the possibility of revealing the antigenic structures which bind to B27 molecules in patients with AS. This could in turn lead to the source of these antigens in the environment. There has been a tendency to assume that one simple model will explain all the B27-associated disorders but it may be preferable to keep an open mind about the possibility that the mechanisms involved in AS, in the bacteria-induced acute arthropathies and in acute anterior uveitis may not be identical. At the same time, there is a need to continue further direct investigation of the role of microbiological agents in AS both in vitro and in vivo, as ultimately it is most likely that, by blocking the effects of such agents as may be shown to be involved, progress in our ability to influence the progress of the disease in a fundamental way will be achieved. There is still little information as to how the tissues involved in AS come to be the particular targets of the pathological process and currently proposed theories of pathogenesis have not yet provided very satisfactory answers to this problem.

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.

Lymphokine mRNA and T cell multireceptor mRNA of the Ig super gene family are reciprocally modulated during human T cell activation

The expression of genes, implicated in T cell proliferation as well as those coding for the three chains of the T cell receptor (TcR) and for the CD4 and CD8 molecules, has been investigated during activation of various T cell populations maintained in long-term culture. We show that a minimal activation signal, capable of inducing interleukin 2 (IL 2) receptor expression without the expression of IL2 and interferon-gamma, was not associated with a down-regulation of the messengers coding for the T cell multireceptor molecules. In contrast, a strong activation signal via the TcR/CD3 complex or via the CD2 molecule resulted in a reciprocal transient up-regulation of the messengers implicated in T cell proliferation and a down-regulation of the messengers encoding the molecules of the TcR complex of the immunoglobulin super gene family.

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.

Molecular analysis of the variant alloantigen HLA-B27d (HLA-B*2703) identifies a unique single amino acid substitution

HLA-B27 is a human major histocompatibility complex class I product defined by its antigenic specificity with conventional alloantisera. Detailed studies using monoclonal antibodies, cytotoxic T lymphocytes (CTL), and isoelectric focusing (IEF) gel electrophoresis demonstrated the heterogeneity in the B27 antigen. We have previously identified a unique variant molecule of B27 designated locally as B27d which is distinguished from other B27 variants by isoelectric point, serologic reactivity, and by a cloned CTL recognition. A gene encoding the B27d variant has been cloned and a complete nucleotide sequence has been determined. Compared to the sequence of the prototype B27a, the B27d has a single base substitution at codon 59 (B27a:TAT--B27d: CAT) in exon 2 responsible for Tyr to His substitution. A His residue at this position in the alpha 1 domain is unique among the known class I sequences and this single amino acid change is apparently sufficient to alter the epitope(s) recognized by antibody and cytotoxic T cell receptor. Previous primary structural analysis of the other five B27 variants has revealed differences of two to four amino acids. The combined structural data on the B27 variants indicate that (1) HLA-B27 represents a family of closely related B locus alleles that share the B27 allospecificity and differ by a limited number (one to four) of amino acid substitutions and (2) point mutation as well as gene conversion might be the mechanism responsible for the allelic variation of B27 antigen family.

Structural analysis of HLA-A2.4 functional variant KNE. Implications for the mapping of HLA-A2-specific T-cell epitopes

HLA-A2 antigens are divided into four subtypes, designated A2.1 to A2.4, by the use of cytolytic T lymphocytes (CTL). The A2.4 subtype consists of a functionally heterogeneous group of variants that are not recognized by A2.1-, A2.2-, or A2.3-specific CTL lines while it is indistinguishable from A2.1 by isoelectric focusing. The structure of an A2.4 variant expressed on donor KNE has been established by comparative peptide mapping with A2.1 and radiochemical sequencing. It was found to differ from A2.1 by a single amino acid change of Cys to Tyr at position 99. This position is only moderately polymorphic and has not previously been found to vary in any other HLA or H-2 variants. The nature of the change is compatible with its generation by one-point mutation from A2.1. The only other previously characterized A2.4 variant, CLA, differs from A2.1 by a single amino acid replacement at position 9. Both residues 9 and 99 are located in homologous positions within the alpha 1 and alpha 2 domains, respectively. The results shown contribute to the molecular interpretation of the heterogeneity of CTL recognition within the HLA-A2.4 group of antigens.

Clonal heterogeneity of HLA-B27 cellular allorecognition. Delineation of immunodominant sites

The fine specificity of nine cytolytic T lymphocyte (CTL) clones obtained after stimulation of HLA-B27- responder lymphocytes with B27.1+ lymphoblastoid cell lines has been analyzed. These clones defined three different reaction patterns when tested against a panel of target cells including those expressing all known HLA-B27 subtypes: (a) specific recognition of HLA-B27.1, B27.2 and B27d, (b) selective reactivity with B27.1, B27d and HLA-B40 and (c) selective recognition of B27.1, B27.2, B27d, B27f and B40. Representative clones within each group were analyzed in detail. Differences in lytic ability of the various susceptible targets within each group were established by cold target inhibition analyses and by blocking experiments with anti-CD3 and anti-CD8 monoclonal antibodies. When correlated with the known structure of the HLA-B27 subtypes, these results demonstrate the critical relevance of amino acid changes within residues 77-81 and at position 152 in modulating allospecific CTL recognition of HLA-B27.1 and suggest that these residues could be involved in the structure of immunodominant regions of this antigen. The observed cross-reactions with HLA-B40, differing from B27.1 in 16 amino acid residues, suggest that the simultaneous occurrence of multiple amino acid changes could have mutually compensatory effects, so that a cross-reactive epitope might result from various combinations of polymorphic residues.

Conventional alloantisera can recognize the same HLA-B27 polymorphism as detected by cytotoxic T lymphocytes

Subtypes of B27 have been identified by cytotoxic T lymphocytes, biochemistry, molecular biology, and murine monoclonal antibodies. In the present study we describe seven B27 subtype-specific pregnancy sera. The reaction pattern of these B27 subtype-specific sera closely parallels the recognition pattern of B27 subtype-specific cytotoxic T lymphocytes. Because the complete amino acid sequence of the studied B27 subtypes (B27W, B27K, B27C, B27D) is known, it can be determined which amino acid substitutions are responsible for recognition by subtype-specific sera and by cytotoxic T lymphocytes, respectively. It is proposed that B27 subtype-specific sera and B27 subtype-specific cytotoxic T lymphocytes recognize the same epitopes or that a single amino acid change can induce multiple antigenic determinants, which are recognized differentially by antibodies and T cells.

HLA-restricted recognition of viral antigens in HLA transgenic mice

Cytotoxic T lymphocytes (CTL) recognize antigen in the context of the class-I products of the major histocompatibility complex (MHC). The extensive polymorphism of class-I molecules is thought to be linked to their capacity to present a large variety of foreign antigens. Whether a single T-cell receptor (TCR) recognizes two separate epitopes (the foreign antigen and an epitope on MHC molecules), or a single epitope resulting from the combination of a foreign antigen and an MHC molecule, has not yet been resolved. In view of the differences between species in primary structure of histocompatibility antigens, it might be predicted that the TCR repertoire would evolve in concert with the diversity of MHC antigens. The mouse and human TCR repertoire would be optimally adapted to engage in productive interactions only with mouse (H-2) and human (HLA) MHC antigens respectively, especially if the more conserved features of histocompatibility antigens, in addition to foreign antigen, were seen by the TCR. Alternatively, only the most variable segments of MHC antigens might be engaged in antigen presentation and thus in interaction with the TCR. In that case, interaction between MHC plus antigen and the TCR might not necessarily be limited by species-specific features. By analysis of the T-cell response against virus-infected cells in HLA-B27/human beta 2-microglobulin double transgenic mice, we report here that the mouse T-cell repertoire is perfectly capable of using the human HLA-B27 antigen as a restriction element.

Association of a 9.2-kilobase Pvu II class I major histocompatibility complex restriction fragment length polymorphism with ankylosing spondylitis

We analyzed DNA restriction fragment length polymorphism (RFLP) in 53 white ankylosing spondylitis (AS) patients and 92 healthy controls, utilizing a full-length HLA-B7 complementary DNA probe. A 9.2-kilobase (kb) Pvu II fragment was found to be significantly increased in frequency in B27 positive AS patients compared with the B27 positive control group (P = 0.00085, relative risk = 7.2). The presence of both B27 and the 9.2-kb RFLP in an individual conferred a relative risk for AS of 297, compared with a relative risk of 119 in those who had B27 alone. The 9.2-kb RFLP appears to be a marker for AS which, with HLA-B27, contributes further to susceptibility to the disease. Our findings indicate that this fragment and HLA-B27 segregate independently in familial studies of AS.

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.

Specific lysis of murine cells expressing HLA molecules by allospecific human and murine H-2-restricted anti-HLA T killer lymphocytes

The lysis by human and murine anti-HLA cytolytic T lymphocytes (CTL) of murine cells expressing class I HLA molecule after gene transfection has been studied using two different murine cells: LMTK- and P815-HTR-TK-. Weak but significant HLA-A11-specific lysis was found occasionally with human CTL on the HLA-A11+ L cells. On the contrary, P815-A11 or P815-A2 cells were lysed strongly and specifically by HLA-A11 or HLA-A2-specific human CTL. The T8+T4- phenotype of the effector cells was confirmed and the reaction was inhibited by anti-HLA class I monoclonal antibodies. Despite their higher sensitivity to human CTL, the P815-HLA+ cells did not express higher levels of HLA antigens than L cells, and the presence or the absence of human beta 2 microglobulin was irrelevant. Anti-human LFA-1 antibodies abrogated the lysis of P815-A11+ cells showing that the LFA-1 receptor which is apparently lacking on the L cell surface was on the contrary expressed on P815 cells. On the other hand, murine anti-HLA CTL have been prepared by immunizing mice against syngeneic HLA-A11+ L cells. They lysed very efficiently and specifically these cells, but appeared completely devoid of activity against human HLA-A11 target cells. This barrier was apparently due to the H-2 restriction of these H-2k anti-HLA murine CTL, as shown by their inability to lyse allogeneic H-2d cells expressing HLA-A11, and by the blocking of their activity by anti H-2k antibodies. By contrast, xenogeneic anti-HLA CTL obtained by immunizing murine lymphocytes against human cells lysed both human and murine HLA+ cells but they reacted with a monomorphic epitope of the HLA molecule in a nonrestricted way. These results show that human cells lyse very efficiently P815 murine cells expressing HLA class I antigens; the higher sensitivity of P815 cells compared to L cells is probably due to the presence of a LFA-1 receptor on these cells; a class I molecule of human origin can be seen as an H-2-restricted minor histocompatibility antigen in another species.

Identification of new B27 subtypes (B27C and B27D) prevalent in oriental populations

With the aid of alloreactive cytotoxic T lymphocytes, three subtypes of HLA-B27 can be defined: B27W, B27K, and B27C (non-B27W and non-B27K). The B27C subtype can be distinguished by 1D-IEF, is not recognized by B27W- or B27K-restricted influenza-A-specific cytotoxic T lymphocytes, and is prevalent in Oriental populations. Preliminary data indicate that the various B27 subtypes (W, K, C) are in different linkage disequilibria with HLA-C antigens. A fourth subtype of B27 (non-B27W and non-B27K), designated as B27D, was detected by 1D-IEF. (See accompanying paper by Neefjes et al.) The finding of four B27 subtypes indicates that the serologically defined B27 antigen comprises a family of various, strongly cross-reactive class-I molecules.

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

Antigen HLA-B27 is a high-risk genetic factor with respect to a group of rheumatoid disorders, especially ankylosing spondylitis. A cDNA library was constructed from an autozygous B-cell line expressing HLA-B27, HLA-Cw1, and the previously cloned HLA-A2 antigen. Clones detected with an HLA probe were isolated and sorted into homology groups by differential hybridization and restriction maps. Nucleotide sequencing allowed the unambiguous assignment of cDNAs to HLA-A, -B, and -C loci. The HLA-B27 mRNA has the structural features and the codon variability typical of an HLA class I transcript but it specifies two uncommon amino acid replacements: a cysteine in position 67 and a serine in position 131. The latter substitution may have functional consequences, because it occurs in a conserved region and at a position invariably occupied by a species-specific arginine in humans and lysine in mice. The availability of the complete sequence of HLA-B27 and of the partial sequence of HLA-Cw1 allows the recognition of locus-specific sequence markers, particularly, but not exclusively, in the transmembrane and cytoplasmic domains.

Despite lack of monospecific anti-DRw13 sera, a corresponding class II determinant can be defined by a DRw13 restricted anti-influenza virus T cell clone

The study of a T3+ T4+ T8- human T cell clone COTC2 with both specific proliferative response and cytolytic activity for influenza A virus infected cells reveals that: the restricting element of this clone is strongly associated with DRw13 molecule(s) as seen by the study of a large panel of antigen presenting cells (APC) and by the observation that monoclonal antibodies (MoAb) specific for DR molecules inhibit its proliferative activity while anti-DQ MoAb do not. These results indicate that there exists a DRw13 associated determinant that can be defined at the functional level by COTC2 recognition despite the absence of monospecific anti-DRw13 serum. In contrast to the results found by other groups, the restriction of this DRw13 restricted clone follows the DRw13 serological definition irrespective of the DW type of the APC. These results indicate that the polymorphism of HLA class II molecules can be further defined at the functional level by monoclonal populations of T cells in conjunction with molecular definition.

Murine cells expressing an HLA molecule are specifically lysed by HLA-restricted antiviral human T cells

Class I HLA (histocompatibility locus antigen) molecules are the targets of allospecific cytolytic T lymphocytes (CTL) in graft rejection, and constitute the restricting elements necessary for the interaction between antiviral CTL and virus-infected cells. Cells expressing only one HLA in the absence of other human molecules would provide a remarkable model for studying the function of these molecules. However, HLA+ murine cells transfected with human genes are generally not lysed by allospecific human CTL, and this is ascribed to insufficient HLA expression, lack of human beta 2-microglobulin, alteration of HLA molecules or absence of receptors for human T8 or LFA1 molecules in murine cells. Here we report, for the first time, the specific lysis of virus-infected HLA+ murine cells by HLA-restricted antiviral human CTL. Therefore, these murine cells constitute an excellent model for studying the role of HLA molecules.

Six variants of HLA-B27 identified by isoelectric focusing

Six variant forms of HLA-B27 were identified among 68 unrelated B27-positive donors by isoelectric focusing (IEF) gel analysis. Each of the six IEF variants was distinguished by charge heterogeneity of desialated B27 heavy chains immunoprecipitated with specific monoclonal antibody (MAb). Charge differences varied from single to several charge units, indicating that these variants may have substantially different amino acid compositions. Informative family study showed that three B27 variant molecules were genetically determined. The uniqueness of these variant molecules was also demonstrable using a panel of alloantisera and MAbs recognizing B27-associated epitopes. Six distinct serological reactivity patterns were observed. Five of these serological patterns correlated with four of the IEF-defined variants, two of these patterns being associated with one IEF variant form. The sixth serological pattern was shared by the remaining two IEF variants. Combining the results of the electrophoretic and serological analyses, it is apparent that there are more than six structural variants within the B27 alloantigen family. Some B27 variant forms were found only in individuals of particular racial origin, indicating that unique genetic variations might occur in different racial groups. In a preliminary analysis of patients with ankylosing spondylitis, no apparent correlation was observed between any specific B27 variants and disease susceptibility.

Structural analysis of an HLA-B27 functional variant: identification of residues that contribute to the specificity of recognition by cytolytic T lymphocytes

The structure of a variant HLA-B27 antigen, B27.2, that is distinguished from the HLA-B27.1 and HLA-B27.3 subgroups by specific cytolytic T lymphocytes has been established by comparative peptide mapping and sequence analysis. There are only three amino acid substitutions between B27.1 and B27.2: aspartate-77, threonine-80, and leucine-81 in HLA-B27.1 are changed to asparagine-77, isoleucine-80, and alanine-81 in HLA-B27.2. These changes account for their single charge difference detectable by isoelectric focusing. The three clustered substitutions of HLA-B27.2 are identical to the corresponding residues in HLA-A24, so that both molecules become identical in their amino acid sequence between residues 72 and 96. This suggests that gene conversion may have occurred during the diversification of the HLA-B27 antigens. HLA-B27.2 has no changes in the alpha 2 domain and is similar in its pattern of substitutions to the murine bm11 mutant. It is suggested that residues 77-81 are of major significance in determining the specificity of cellular recognition of class I HLA antigens. This study, together with the previous analyses of HLA-B27.1 and HLA-B27.3, completes the structural characterization of the three major HLA-B27 functional subtypes and establishes the molecular basis of their functional and serological differences.

Fine specificity analysis of human influenza-specific cloned cell lines

Influenza-specific human-T-cell clones, proliferating in the presence of virus-infected cells with restriction by class II molecules and displaying class II-restricted CTL activity or specific helper activity in antibody synthesis, have been analyzed for antigenic specificities. All of them were obtained by in vitro stimulation against influenza A/Texas virus. In all cases the virus specificity appeared identical in cytolytic and proliferative responses. Three of the clones were broadly cross-reactive, recognizing all or almost all type A influenza strains. The three remaining clones were subtype specific when tested with human strains and recognized the surface glycoproteins of influenza virus. One of these lines reacted with an epitope of the neuraminidase N2 while the other two recognized the hemagglutinin H3. By using a large panel of mammalian and avian influenza strains, it can be demonstrated that hemagglutinin-specific human T cells can recognize a cross-reacting determinant shared by H3 and H4 subtypes of hemagglutinin which has never been detected with antibodies.

Molecular variants of the HLA-B27 antigen in healthy individuals and patients with spondylarthropathies

Despite major advances in genetic and structural studies of the HLA-B27 antigen, the underlying mechanism responsible for the remarkable association between this antigen and spondylarthropathies remains unknown. At a molecular level, the use of B27M1 and B27M2 monoclonal antibodies has permitted the identification of distinct allospecific epitopes on the B27 molecule. One of these epitopes, B27M2, is polymorphic and has allowed us to define B27 variants: B27M2[+], B27M2[-], and B27M2[int]. The heterogeneity of the B27 antigen correlates well with biochemical and cytotoxic evidence of genetic heterogeneity. These variants exhibit ethnic variation and also appear to correlate, in preliminary studies, with disease susceptibility, especially among Orientals. HLA gene probing is potentially an even more precise tool than monoclonal antibodies for the study of MHC-related disease susceptibilities. Initial work in our laboratory has resulted in the production of probes with specificity for HLA-B locus genes and current efforts are directed toward the derivation of B27 allele-specific probes. It seems likely that, when such probes are applied to B27-positive individuals, complexity in addition to the B27M2 variants will be revealed. Yet to be defined is the mechanism behind the association between B27 and AS. Is the association causal for disease, or is B27 indeed just a marker for other pathogenic factors somehow linked to it? Available evidence points to both causal and linked roles for B27 in ankylosing spondylitis. Products of both HLA and non-HLA gene families may interact with infectious disease pathogens in susceptible individuals to produce a disorder which may not be specific in its association with any one pathogenic factor.

Structural analysis of the functional sites of class I HLA antigens

Considerable knowledge of the molecular organization of class I HLA antigens has been attained through extensive structural analysis of these proteins and their genes. Particularly, the nature and location of the polymorphic regions has been established, as well as the basic patterns of structural variability. This work has not unveiled the functionally relevant sites of the HLA molecules but has provided the basis to develop new strategies to do so. The molecular analysis of the determinants recognized by specific antibodies and cytolytic T lymphocytes is being approached through the biochemical characterization of mutants induced in vitro and population variants that are selected by their loss of specific serological or CTL allodeterminants. Other approaches include the immunological analysis of sera raised against synthetic peptides whose structure mimics highly variable segments of class I HLA molecules. These studies have already revealed the participation of several regions in specific allorecognition by antibodies or CTLs and their potential is becoming increasingly evident. A new and possibly powerful approach is currently being used for the dissection of functional sites. It makes use of the structural information derived from sequence analysis and involves expression of cloned HLA genes in transfected mouse or human cells in conjunction with site-directed mutagenesis techniques. Although some difficulties still lie ahead in developing a system suitable for functional assays, the possibility of tailoring HLA mutants and studying the modulation of their recognition determinants by predetermined structural alterations open new pathways to the molecular analysis of HLA function.