Molecular manipulation with the arthritogenic epitopes of the G1 domain of human cartilage proteoglycan aggrecan

Systemic immunization of BALB/c mice with human cartilage proteoglycan (PG) aggrecan induces progressive polyarthritis. The G1 domain of the PG aggrecan molecule contains most of the T cell epitopes, including three immunodominant ('arthritogenic') and at least six subdominant T cell epitopes. The three dominant T cell epitopes (P49, P70 and P155) were deleted individually or in combination by site directed mutagenesis, and the recombinant human G1 (rhG1) domain (wild type and mutated) proteins were used for immunization. Close to 100% of BALB/c mice immunized with the wild-type (nonmutated) rhG1 domain developed severe arthritis, which was 75% in the absence of P70 (5/4E8) epitope, and very low (< 10% incidence) when all three dominant T cell epitopes were deleted. The onset was delayed and the severity of arthritis reduced in animals when dominant T cell epitopes were missing from the immunizing rhG1 domain. The lack of T cell response to the deleted epitope(s) was specific, but the overall immune response against the wild-type rhG1 domain of human PG was not significantly affected. This study helped us to understand the dynamics and immune-regulatory mechanisms of arthritis, and supported the hypothesis that the development of autoimmune arthritis requires a concerted T cell response to multiple epitopes, rather than the immune response to a single arthritogenic structure.     

Continuous nasal administration of antigen is critical to maintain tolerance in adoptively transferred autoimmune arthritis in SCID mice

Mucosal tolerance is a natural mechanism that prevents immunological reactions to antigens by altering the activity of immune cells of pathogenic clones without modulating the entire immune system. This 'natural immune suppression' can be exploited when antigen(s) of the target organ in an autoimmune disease is used for mucosal treatment. Being inspired by the experimental results in animal models, clinical trials using type II collagen for mucosal treatment have been conducted in rheumatoid arthritis. High-density proteoglycan (aggrecan) is another major macromolecular component in articular cartilage, and may be a candidate autoantigen for provoking immune reactions in patients with rheumatoid arthritis. Indeed, like type II collagen, systemic immunization of genetically susceptible mice with proteoglycan (PG) aggrecan induces progressive autoimmune polyarthritis. Here, we investigated whether intranasally applied PG can be effective in suppressing PG-induced arthritis (PGIA) in BALB/c mice. We found that nasal administration of 100 microg PG exerted a strong suppressive effect on both the incidence and severity of the disease, most probably by reducing responsiveness towards the immunizing PG antigen. When we transferred PGIA into genetically matched but immunodeficient SCID mice, we were able to establish a tolerized state, but only if the recipient SCID mice received lymphocytes from tolerized animals and intranasal treatment with PG was continued. Without nasally administered antigen, the transferred anergic cells recovered and arthritis rapidly developed in a severe form. Intranasal PG treatment of recipient SCID mice was ineffective when cells from non-tolerized arthritic donors were transferred, in which case the regular weekly 'tolerizing' dose of PG made the disease worse. Our results suggest that mucosal treatment in an already existing disease may result in paradoxical outcomes.     

从健康人外周血建立人软骨抗原凝集原G1区自身反应性T淋巴细胞株

为了研究健康人T细胞库中是否存在G1特异性T细胞 ,我们应用重组人软骨抗原凝集原G1为抗原 (rG1) ,采用国际标准半有限稀释建系法 ,从 4名正常人外周血中建立了 11株rG1特异性T细胞系。 4名健康供者的rG1特异性T细胞系出现频率分别为 0 6 / 10 6(RP )、 0 5 / 10 6(AC )、 1 6 / 10 6(YZ )和 2 0 / 10 6(JY ) ,平均为 1 1± 0 5 / 10 6。远远低于类风湿性关节炎病人外周血rG1特异性自身反应性T细胞。所有T细胞系与rG1及WT和PPD共同培养以观察其特异性反应性 ,结果发现所建立的 11株T细胞系对人软骨抗原凝集素G1区具有良好的特异性。本研究结果提示正常人外周血中确有rG1特异性T细胞系 ,但是出现频率远远低于类风湿性关节炎病人 (另文报道 )。     

Immunity to homologous collagens and cartilage proteoglycans in rabbits.

The in vitro incorporation of [3H]-thymidine into spleen cells was used to show that rabbits with experimentally-induced inflammatory arthritis of 1-4 months duration often develop cellular immunity to purified homologous cartilage proteoglycans, type I and III collagens and, less frequently, to type II collagen. Responses to collagens were primarily directed to antigenic determinants exposed on peptides in degraded molecules, whereas responses to proteoglycans were seen with both native and degraded molecules. These in vitro blastogenic responses were shown to be completely dependent on the presence of T lymphocytes in the cultures. This expression of immunity was not demonstrable in rabbits with long duration arthritis (7-12 months) with any of the antigens tested. Some rabbits injected with homologous proteoglycans demonstrated T-cell-dependent cellular, but not humoral, immunity to the injected antigens. In contrast, rabbits injected with heterologous human proteoglycans developed cellular and humoral immunity to the immunizing proteoglycan, but failed to develop cellular immunity to rabbit proteoglycan. Some of these rabbits did, however, produce circulating antibodies which reacted with rabbit proteoglycans. Moreover, antibodies produced by immunizing rabbits with proteoglycans from bovine, chicken and rat cartilages and the hyaluronic acid binding region from rat cartilage proteoglycan often cross-reacted with rabbit proteoglycan, indicating that there are species-common antigenic determinants present in these proteoglycans and in the hyaluronic acid binding region and that these are recognizable in rabbit proteoglycans by rabbit antibodies. This ability to induce selectively cellular or humoral immunity to proteoglycans should be useful for future investigations of the role of such immunity in the pathogenesis of arthritis, although induction of immunity to proteoglycan was not accompanied by any demonstrable synovitis in these rabbits as has been observed in some strains of rats and mice for type II collagen.     

The cartilage collagens: a review of their structure, organization, and role in the pathogenesis of experimental arthritis in animals and in human rheumatic disease

This contribution reviews the structure and organization of collagen molecules found in cartilage and the roles that they may play in rheumatic diseases. Cartilage is unique in its physical properties and molecular composition, and contains sufficient amounts of types II, IX, X, and XI collagen to deem these molecules as ”cartilage-specific.” The vitreous body of the eye, a ”cartilagelike” tissue is also rich in the same collagens but is type X deficient. Types VI and XII collagen are present in cartilage as well as noncartilaginous tissues. Types II, IX, and XI collagen are organized into matrix fibrils, where type II constitutes the bulk of the fibril, type XI regulates fibril size, and type IX facilitates fibril interaction with proteoglycan macromolecules. Genetic defects in these collagens can produce mild to severe developmental abnormalities, including spondyloepiphyseal dysplasia often accompanied by an accelerated form of osteoarthritis. Sensitization with collagen can produce experimental rheumatic diseases. Type II collagen induces an erosive polyarthritis in certain strains of rats, mice, and higher primates which can resemble rheumatoid arthritis and relapsing polychondritis. Type XI collagen is arthritogenic in rats but not mice; type IX induces autoimmunity in both species but not arthritis. Arthritis is initiated by complement fixing antibodies that bind to type II collagen in autologous cartilage, and the production of these antibodies is MHC restricted and T cell dependent. It is unclear whether T cells alone can induce arthritis, although they probably help sustain it. Mapping and characterizing the of T cell epitopes on type II collagen has resulted in the synthesis of small homolog and substituted peptides of type II collagen which suppress arthritis in an antigen-specific manner by a variety of routes, including mucosal. Moreover, collagen-induced arthritis has proven a valuable model to study the contribution of cytokines and other biological agents in the pathogenesis of joint injury and how they might be used to develop new therapies. Collagen autoimmunity has been implicated in the pathogenesis rheumatoid arthritis and polychondritis. Circulating antibodies to type II collagen are found in both diseases. Antibodies to types IX and XI collagen are also present in rheumatoid sera but are less prevalent. Rheumatoid cartilage and synovium contain antibodies to type II collagen at a prevalence far greater than serum, suggesting an intra-articular antigen-driven immune process. Although effective in animal models, attempts to treat rheumatoid arthritis with orally administered type II collagen have proven elusive. Different approaches using newer formulations and selected or modified oligopeptides remain to be tested and could prove effective in the treatment of the human rheumatic diseases. Received: 16 April 1997 / Accepted: 15 January 1998     

Unconventional T‐cell recognition of an arthritogenic epitope of proteoglycan aggrecan released from degrading cartilage

It has been proposed that peptide epitopes bind to MHC class II molecules to form distinct structural conformers of the same MHC II–peptide complex termed type A and type B, and that the two conformers of the same peptide–MHC II complex are recognized by distinct CD4 T cells, termed type A and type B T cells. Both types recognize short synthetic peptides but only type A recognize endosomally processed intact antigen. Type B T cells that recognize self peptides from exogenously degraded proteins have been shown to escape negative selection during thymic development and so have the potential to contribute to the pathogenesis of autoimmunity. We generated and characterized mouse CD4 T cells specific for an arthritogenic epitope of the candidate joint autoantigen proteoglycan aggrecan. Cloned T‐cell hybridomas specific for a synthetic peptide containing the aggrecan epitope showed two distinct response patterns based on whether they could recognize processed intact aggrecan. Fine mapping demonstrated that both types of T‐cell recognized the same core epitope. The results are consistent with the generation of aggrecan‐specific type A and type B T cells. Type B T cells were activated by supernatants released from degrading cartilage, indicating the presence of antigenic extracellular peptides or fragments of aggrecan. Type B T cells could play a role in the pathogenesis of proteoglycan‐induced arthritis in mice, a model for rheumatoid arthritis, by recognizing extracellular peptides or protein fragments of joint autoantigens released by inflamed cartilage.     

Differential detection of type II collagen N-terminal and C-terminal denaturation epitopes in degrading cartilage.

AIMS: To investigate the relative stability of collagen metabolites in degrading cartilage. METHODS: New antipeptide antibodies to denaturation epitopes located in the N-terminal and C-terminal regions of the type II collagen helix have been made and characterized. Type II collagen fragments in the conditioned medium from cultures of degrading bovine nasal cartilage were detected by immunoblotting with the new antisera as well as by N-terminal sequencing. The antibodies were also used in immunohistochemical studies of normal and osteoarthritic human cartilage. RESULTS: Type II collagen fragments with an apparent molecular mass of approximately 30 kDa were detected in cartilage conditioned media using antibody AH12L3, which recognizes N-terminal epitope AH12. The N-terminal sequence of one of these fragments matched exactly a sequence in the N-terminal region of type II collagen. Antibody AH9L2, which recognizes C-terminal epitope AH9, did not bind to any protein bands in the immunoblotted culture medium. In immunohistochemical studies, antibody AH12L3 detected extensive regions of degraded collagen in osteoarthritic cartilage and a more restricted pattern of staining in nonarthritic cartilage. Far less immunostaining was apparent in all cartilage specimens with antibody AH9L2. CONCLUSIONS: These results indicate that the N-terminal region of type II collagen is more resistant to proteolysis than the C-terminal region, an observation that has important implications for the choice of epitopes that are likely to be good markers of damage to cartilage collagen in patients with arthritis.     

Differential detection of type II collagen N-terminal and C-terminal denaturation epitopes in degrading cartilage.

AIMS: To investigate the relative stability of collagen metabolites in degrading cartilage. METHODS: New antipeptide antibodies to denaturation epitopes located in the N-terminal and C-terminal regions of the type II collagen helix have been made and characterized. Type II collagen fragments in the conditioned medium from cultures of degrading bovine nasal cartilage were detected by immunoblotting with the new antisera as well as by N-terminal sequencing. The antibodies were also used in immunohistochemical studies of normal and osteoarthritic human cartilage. RESULTS: Type II collagen fragments with an apparent molecular mass of approximately 30 kDa were detected in cartilage conditioned media using antibody AH12L3, which recognizes N-terminal epitope AH12. The N-terminal sequence of one of these fragments matched exactly a sequence in the N-terminal region of type II collagen. Antibody AH9L2, which recognizes C-terminal epitope AH9, did not bind to any protein bands in the immunoblotted culture medium. In immunohistochemical studies, antibody AH12L3 detected extensive regions of degraded collagen in osteoarthritic cartilage and a more restricted pattern of staining in nonarthritic cartilage. Far less immunostaining was apparent in all cartilage specimens with antibody AH9L2. CONCLUSIONS: These results indicate that the N-terminal region of type II collagen is more resistant to proteolysis than the C-terminal region, an observation that has important implications for the choice of epitopes that are likely to be good markers of damage to cartilage collagen in patients with arthritis.     

Proteoglycan-induced arthritis: immune regulation, cellular mechanisms, and genetics

Rheumatoid arthritis is probably the least understood systemic autoimmune disease, and it affects approximately 1% of the human population. Several lines of evidence indicate that the effector mechanism, which initially attacks small joints, is T-cell driven. As a result, an aggressive synovial pannus develops, which destroys articular cartilage and bone, leading to massive ankylosis and deformities of peripheral joints. The disease has a progressive character, with the involvement of more and more joints. Although the target organ is the synovial joint, there is no clear evidence that any macromolecule of cartilaginous tissues, bone, or synovium, could be a preferential autoantigen. There are numerous rodent models that simulate some or many of the clinical, immunological, or histopathological features of the disease. Recently, it has become a strong working hypothesis that MHC and non-MHC genetic components share loci that are common in various autoimmune diseases, and in corresponding animal models. The most relevant animal models of rheumatoid arthritis appear to be those induced by cartilage matrix components such as type II collagen or proteoglycan aggrecan. This review summarizes our current knowledge of cartilage proteoglycan (aggrecan)-induced arthritis in mice.     

Immunization of rats with homologous type XI collagen leads to chronic and relapsing arthritis with different genetics and joint pathology than arthritis induced with homologous type II collagen

The most commonly used animal model for rheumatoid arthritis (RA) is collagen-induced arthritis (CIA), induced by immunization with type II collagen (CII), a cartilage restricted protein. In this work we show that type XI collagen (CXI), which is a minor component in cartilage, induces a different form of erosive and chronic relapsing polyarthritis in rats. Using a series of inbred rat strains involving various genetic backgrounds (DA, LEW, E3), and congenic MHC regions (a, u, f, n, c, d), we found that CXI induced arthritis (C(XI)IA) is associated with the RT1f haplotype in contrast to CII induced arthritis (C(II)IA), which is associated with the RT1a and RT1u haplotypes. The C(XI)IA follows a chronic disease course affecting peripheral joints with both progression and relapses, which appear not to cease (occurring >800 days). Susceptible strains showed a sustained antibody response to CXI with time indicating that the autoimmune response was self-perpetuated. Microscopic analysis of the joints at different stages demonstrated the severe destruction of bone and cartilage by pannus tissue consisting of activated macrophages and T cells. The main difference to joints from rats with C(II)IA was larger numbers of infiltrating lymphocytes and these tended to form follicle-like aggregates. Surprisingly, males were more susceptible to C(XI)IA than females whereas the opposite has been observed in other rat arthritis models, including C(II)IA. Taken together, C(XI)IA is a chronic relapsing and erosive polyarthritis that is MHC associated, which in fact fulfills the criteria for diagnosis of RA. Thus the C(XI)IA model will be useful as a novel and relevant animal model for RA.     

Relapsing arthritis induced by cell transfer from collagen-immunised mice

Collagen-induced arthritis is a well-established model of chronic inflammatory arthritis. We here introduce a development of this model which combines the benefits of adoptive transfer and sequential relapse. DBA/1 x B10.Q F1 hybrid mice were immunised with bovine type II collagen, and those which developed a sufficiently high level of arthritis served as donors of spleen cells transferred into BALB/c SCID hosts. After boosting with 500 microg collagen, the development of host arthritis was monitored over a period of up to 256 days, during which up to three successive peaks were detected. In comparison with bovine collagen, mouse collagen used for boosting induced a lower initial peak but higher relapses. As expected, the transferred disease was more uniform than the freshly induced one. Previous information suggests that a shifting cytokine balance between protective and aggressive T cells may account for the relapse and remission. This study provides a model of relapsing polyarthritis, obtained with normal immunocytes boosted with a well-defined protein antigen in animals not themselves treated with adjuvant. As such it is relevant to the etiology of inflammatory arthritis in man, and, if further developed, could be of value for testing new therapeutic strategies.     

Immunopathologic Role of Proteoglycan Antigens in Rheumatoid Joint Disease

Cell-mediated immunity to proteoglycan antigens was assessed by leucocyte migration inhibition and by lymphocyte stimulation tests in patients with rheumatoid arthritis or with ankylosing spondylarthritis, in patients with relapsing synovitis after a single trauma to their knee joints, and in healthy donors. Both tests revealed a sensitization in most of the patients examined with various proteoglycan antigens derived from human cartilaginous tissues, rheumatoid synovial fluid, and species-common antigen of bovine nasal cartilage. Anybodies against proteoglycan antigens of human articular cartilage were detected by solid-phase radioimmunoassay in eleven out of twenty-nine sera from patients with rheumatoid arthritis and in four out of six rheumatoid synovial fluids. The results suggest that the cartilage antigenic components released by an inflammatory process or trauma may trigger a vicious circle of chronic inflammation and joint destruction.     

Mice lacking matrilin-1 (cartilage matrix protein) have alterations in type II collagen fibrillogenesis and fibril organization.

Matrilin-1 (cartilage matrix protein) is a homotrimeric protein that forms collagen-dependent and collagen-independent fibrils in the extracellular matrix of cartilage. In the growth plate of developing long bones, the gene for matrilin-1 is transcribed exclusively by the chondrocytes of the zone of maturation which is situated between the zones of proliferation and hypertrophy. When associated with the cartilage collagen fibril, which consists of collagens type II, IX, and XI, matrilin-1 displays a periodicity of 59.3 nm. Matrilin-1 also interacts with the proteoglycan, aggrecan. Because of its association with the collagen fibril, we tested the hypothesis that matrilin-1 may play a role in collagen fibril formation and cartilage matrix assembly by generating mice with targeted mutations in the matrilin-1 gene. Ultrastructural studies of the cartilage of growth plates of matrilin-1 null mice reveal an abnormal type II collagen fibrillogenesis and fibril organization in the matrix of the zone of maturation. These results represent the first report on the regulation of the heterotypic type II collagen fibril by a non-collagenous protein. The abnormal fibrillogenesis had no obvious effects on skeletal development, on the organization of chondrocytes in the growth plate and on the deposition of aggrecan and the hypertrophic-specific type X collagen in the cartilaginous matrix.     

Incorporation of an aggrecan mimic prevents proteolytic degradation of anisotropic cartilage analogs

Biomimetic scaffolds that promote regeneration and resist proteolysis are required as a tissue engineering solution to repair or replace a broad range of diseased tissues. Native corrosive environments, such as the richly enzymatic milieu of diseased articular cartilage, degrade the local extracellular matrix structure, so an implantable replacement must both replicate the healthy structure and demonstrate substantial proteolytic immunity, yet promote regeneration, if long-term functional success is to be achieved. Here, we combine magnetically aligned collagen with peptidoglycans, biosynthetic molecules that mimic proteoglycan activity but lack core proteins susceptible to proteases, to develop cartilage scaffold analogs with tailored functionality. With the incorporation of the aggrecan mimic, we demonstrate an ability to enhance bulk mechanical properties and prevent cytokine-induced degradation. Furthermore, fiber alignment in collagen scaffolds enhanced the gene expression of aggrecan, indicating cell responsiveness to anisotropy that also better replicates the natural environment of cartilage. Finally, the expression of type II collagen is enhanced with both alignment and incorporation of the aggrecan mimic, showing synergism between fiber alignment and incorporation of the aggrecan mimic. The work presented here identified a mechanistic synergy of matrix molecules and organization to prevent proteolysis while simultaneously upregulating protein expression.     

Defects in articular cartilage metabolism and early arthritis in fibroblast growth factor receptor 3 deficient mice

Fibroblast growth factor (FGF) receptor 3 has been identified as a key regulator of endochondral bone development and of post-natal bone metabolism through its action on growth plate chondrocytes and osteoblasts, respectively. It has also been shown to promote chondrogenesis and cartilage production by cultured pre-chondrogenic cells in response to FGF18. In the current studies, we show that the absence of signaling through Fgfr3 in the joints of Fgfr3(-/-) mice leads to premature cartilage degeneration and early arthritis. Degenerative changes in cartilage matrix included excessive proteolysis of aggrecan core protein and type II collagen, as measured by neo-epitope immunoreactivity. These changes were accompanied by increased expression of metalloproteinase MMP13, type X collagen, cellular hypertrophy and loss of proteoglycan at the articular surface. Using a novel micro-mechanical indentation protocol, it was shown that articular cartilage in the humeral head of 4-month-old Fgfr3(-/-) mice was less resistant to compressive force and less stiff than that of littermate controls. These results identify Fgfr3 signaling as a potential target for intervention in degenerative disorders of cartilage metabolism.     

Suppression of autoimmune responses and inflammatory events by leflunomide in an animal model for rheumatoid arthritis

The effect of leflunomide (HWA 486) was tested in proteoglycan-induced arthritis in an autoimmune animal model showing many similarities to human rheumatoid arthritis and ankylosing spondylitis. The development of the disease in genetically susceptible BALB/c mice is dependent upon the expression of both cell-mediated and humoral immunity to host mouse cartilage proteoglycan. Arthritic and control (non-arthritic) animals were treated with 35 mg leflunomide/kg body weight/day for 12 weeks to suppress inflammatory events and antibody titers. Leflunomide suppressed acute inflammatory events, protected animals from new inflammatory episodes and acute exacerbations, slightly reduced the stiffness in joints and blocked the degradation of cartilage. The suppressive effect of leflunomide in proteoglycan-induced arthritis is due primarily to the suppression of autoantibody formation.     

Suppression of autoimmune responses and inflammatory events by leflunomide in an animal model for rheumatoid arthritis

The effect of leflunomide (HWA 486) was tested in proteoglycan-induced arthritis in an autoimmune animal model showing many similarities to human rheumatoid arthritis and ankylosing spondylitis. The development of the disease in genetically susceptible BALB/c mice is dependent upon the expression of both cell-mediated and humoral immunity to host mouse cartilage proteoglycan. Arthritic and control (non-arthritic) animals were treated with 35 mg leflunomide/kg body weight/day for 12 weeks to suppress inflammatory events and antibody titers. Leflunomide suppressed acute inflammatory events, protected animals from new inflammatory episodes and acute exacerbations, slightly reduced the stiffness in joints and blocked the degradation of cartilage. The suppressive effect of leflunomide in proteoglycan-induced arthritis is due primarily to the suppression of autoantibody formation.

     

Intramolecular polyspecificity in CD4 T‐cell recognition of Ad‐restricted epitopes of proteoglycan aggrecan

T‐cell recognition of MHC–peptide complexes shows a high degree of polyspecificity extending to recognition of a large number of structurally unrelated peptides. Examples of polyspecificity reported to date are confined to recognition of epitopes from distinct proteins or synthetic peptide libraries. Here we describe intramolecular polyspecificity of CD4 T cells specific for several epitopes within proteoglycan aggrecan, a structural glycoprotein of cartilage and candidate autoantigen in rheumatoid arthritis. T‐cell hybridomas from aggrecan‐immunized mice recognized four structurally unrelated epitopes from the G1 domain of aggrecan, but not other aggrecan epitopes or a variety of other peptide epitopes restricted by the same MHC class II allele. We also showed that the hierarchy of cross‐reactivity broadly correlated with the strength of peptide binding to MHC class II. Similar polyspecificity was observed in responses of lymph node cells from peptide‐immunized mice, suggesting polyspecificity of a significant proportion of the in vivo aggrecan specific T‐cell repertoire. Polyspecific recognition of several epitopes within the same autoantigen may provide a novel mechanism to reach the activation threshold of low‐affinity autoreactive T cells in the initiation of autoimmune diseases.     

软骨蛋白多糖及其在骨关节病中的作用

软骨蛋白多糖及其在骨关节病中的作用赵明（中国医学科学院，中国协和医科大学，生物医学工程研究所天津３００１９２）蛋白多糖是一类由多种长链氨基多糖连接在一个蛋白核心上而构成的糖蛋白，由于在此类糖蛋白中，糖的含量远远高于蛋白的含量（可占整个糖蛋白的９０％以...     

Mapping of B-cell epitopes on the outer membrane P2 porin protein of Haemophilus influenzae by using recombinant proteins and synthetic peptides.

The P2 protein of Haemophilus influenzae type b has a porin activity and is the most abundant protein in the outer membrane. We have employed fusion protein constructs and synthetic peptides along with monoclonal antibodies to map B-cell epitopes in this protein. A linear, surface-exposed epitope was identified between residues 158 and 174. A second surface-exposed epitope was identified near the carboxy-terminal end of the protein (residues 319 to 341). Two additional B-cell epitopes were identified. One was localized between residues 28 and 55, whereas the other was located between residues 148 and 174. These epitopes were not present on the surface of intact H. influenzae cells. Thus, four distinct immunogenic and antigenic regions on the P2 protein have been identified.