Differential immune responses to Borrelia burgdorferi in European wild rodent species influence spirochete transmission to Ixodes ricinus L. (Acari: Ixodidae)

Immune responses to Borrelia burgdorferi and their influence on spirochete transmission to Ixodes ricinus were analyzed in the natural European reservoir hosts; i.e., the mouse species Apodemus flavicollis (yellow-necked mouse) and Apodemus sylvaticus (wood mouse) and the vole species Clethrionomys glareolus (bank vole), and, in addition, in the laboratory mouse strain NMRI. Naive and preimmunized rodents were infected either by artificially infected I. ricinus larvae or by intradermal injection of spirochetes. Independent of the species, all animals developed antibodies to various spirochetal antigens. However, antibodies to the outer surface proteins A (OspA) and B (OspB) were not found in recipients infected via ticks. Rodents of the genus Apodemus and of the NMRI strain showed higher levels of B. burgdorferi-specific antibodies than those of the species C. glareolus. The rate of spirochete transmission to noninfected ticks correlated with both the quality and quantity of spirochete-specific antibodies generated in the various species: high levels of spirochete-specific immunoglobulins correlated with low transmission rates. Furthermore, lower transmission rates were observed with rodents expressing antibodies to OspA and OspB (i.e., intradermally infected or immunized) than with those lacking these specificities (i.e., infected via ticks). The study provides evidence that transmission of B. burgdorferi from natural hosts to ticks is controlled by the specificity and quantity of spirochete-reactive antibodies and suggests that immunity to B. burgdorferi in natural reservoir hosts is an important regulatory factor in the horizontal transmission of B. burgdorferi in nature.

A 14,000 MW lipoprotein and a glycolipid-like structure of Borrelia burgdorferi induce proliferation and immunoglobulin production in mouse B cells at high frequencies

Sonicated preparations of Borrelia burgdorferi are able to stimulate unselected resting BALB/c spleen cells to proliferate and to produce immunoglobulin in vitro. FACS analysis of target cells prestained with an integrated cell-surface marker as well as cell-depletion experiments demonstrate that the majority of responding lymphocytes are B cells. Limiting dilution analyses of resting B cells revealed high frequencies of cells producing IgM (F 1/11-1/62) or IgG (F 1/5-1/163) in response to B. burgdorferi sonicate (B.b. sonicate). These numbers were similar to those obtained with lipopolysaccharide (LPS) (IgM: F 1/20-1/84; IgG: F 1/14-1/85) or a synthetic lipopeptide of Braun's Escherichia coli lipoprotein (IgM: F 1/15, 1/19; IgG: F 1/148, 1/34). The mitogenic structure(s) expressed by B. burgdorferi is distinct from LPS, as similar proliferative responses were obtained with B cells from LPS-resistant (C57BL/10ScCr and C3H/HeJ) and LPS-susceptible (C57BL/10ScSn, C3H/HeN) mice. Furthermore, B-cell mitogenic properties were also found in two distinct fractions of a phenol-chloroform-petroleum ether extract of B. burgdorferi: they consisted of a lipoprotein distinct from the outer surface proteins (Osp) A and B and glycolipid-like structures, respectively. These data suggest that spirochetes express a multitude of distinct structures with mitogenic activity for B cells including various lipoproteins as well as glycolipid(s).

Borrelia burgdorferi upregulates the adhesion molecules E-selectin, P-selectin, ICAM-1 and VCAM-1 on mouse endothelioma cells in vitro

In order to obtain more information on processes leading to Borrelia burgdorferi-induced inflammation in the host, we have developed an in vitro model to study the upregulation of cell surface expression of adhesion molecules on endothelial cells by spirochetes. A mouse endothelioma cell line, derived from brain capillaries, bEnd3, was used as indicator population. bEnd3 cells were incubated with preparations of viable, inactivated or sonicated spirochetes and the expression of E-selectin, P-selectin, ICAM-1 and VCAM-1 was monitored by immunocytochemistry and quantified by cell surface ELISA. We show that all three spirochetal preparations are able to upregulate cell surface expression of E-selectin, P-selectin, ICAM-1 and VCAM-1 on bEnd 3 cells in a dose-dependent manner. The kinetics of cell surface expression of the individual adhesion molecules in the presence of Borrelia burgdorferi showed maxima at about 50 h of incubation or later; this was distinct from results obtained with sonicated-preparations of Escherichia coli bacteria or with enterobacterial LPS where peak expression was observed between 4 h and 16 h. The fact that Borrelia burgdorferi does not contain conventional LPS suggests that the mode of induction of adhesion molecules on endothelial cells is influenced by the phenotype of bacteria. At the peak of spirochete-induced cell surface expression of adhesion molecules (approximately 50 h), bEnd3 cells were found to bind cells of a VLA-4+ B lymphoma line (L1-2) much more efficiently than untreated control cells. The binding of L1-2 cells to presensitized bEnd3 cells was significantly inhibited (more than 75%) in the presence of monoclonal antibodies to both VLA-4 and its endothelial counterreceptor VCAM-1. These findings demonstrate that Borrelia burgdorferi organisms are able to induce functionally active adhesion molecules on endothelial cells in vitro and suggest that E-selectin, P-selectin, ICAM-1 and VCAM-1 play an important role in the pathogenesis of spirochetal infection.

Killing of Borrelia burgdorferi by macrophages is dependent on oxygen radicals and nitric oxide and can be enhanced by antibodies to outer surface proteins of the spirochete

Interaction of B. burgdorferi organisms with mouse bone marrow-derived macrophages (BMM phi) leads to phagocytosis of microorganisms, induction of nitric oxide (NO) and superoxide radicals (O2-) by BMM phi and killing of spirochetes. Destruction of spirochetes by BMM phi was quantified by a new method based on the release of radioactivity from spirochetes pre-labelled with [3H]adenine. Uptake of B. burgdorferi by BMM phi, which mainly occurs by coiling phagocytosis, generation of NO and O2- radicals as well as killing of spirochetes were significantly enhanced by pre-opsonization of spirochetes with monoclonal antibodies (mAb) to the outer surface proteins A and B but not with those to the periplasmic flagellin. Addition of inhibitors specific for NO and O2- radical synthesis either separately or together to cultures of BMM phi and spirochetes resulted in only partial reduction of the killing potential of effector cells. The data indicate that NO and O2- radicals are necessary, but not sufficient, for complete elimination of B. burgdorferi by macrophages. Together with previous findings that protection against B. burgdorferi infection is conveyed by humoral immune responses the present data indicate that one of the important functions of specific antibodies is their participation in macrophage-mediated control of spirochetes.

Protection against Borrelia burgdorferi infection in SCID mice is conferred by presensitized spleen cells and partially by B but not T cells alone

Borrelia burgdorferi induces spirochetemia, arthritis, carditis and myositis in SCID mice but not in immunocompetent co-isogenic C.B-17 mice. The contribution of naive or presensitized B and T cells in the control of spirochetal infection has now been analysed in SCID mice reconstituted with unselected spleen cells or enriched B or T cell populations thereof and subsequently challenged with B. burgdorferi. It is shown that SCID mice were protected (i) completely against disease (arthritis, carditis, myositis) by unselected spleen cells previously sensitized either to intact spirochetes or to recombinant outer surface protein A (OspA), (ii) to a large extent by mixtures of enriched spirochete-specific B and T cells, (iii) partially by equivalent preparations of presensitized B cells or by naive spleen or B cells, and (iv) not at all by presensitized or naive T cells alone. The degree of protection transferred was similar for the corresponding lymphocyte populations presensitized either to viable spirochetes or to recombinant OspA and correlated mainly with serum levels of B. burgdorferi-specific antibodies, in particular those to OspA/OspB. The capacity of enriched presensitized or naive B cells alone to generate specific antibodies of the isotypes IgM, IgG2b and IgG3, and to confer partial protection to SCID mice upon challenge with B. burgdorferi is most probably due to a B cell mitogen(s) associated with the spirochetes. These data further emphasize the important role of B cells and antibodies in the control of B. burgdorferi infection in mice, and suggest that T cells are critically involved in the optimal generation of protective antibody responses but not in the direct elimination of spirochetes from the host.

Molecular and immunological characterization of a novel polymorphic lipoprotein of Borrelia burgdorferi

We describe the cloning, expression, and molecular characterization of a novel polymorphic Borrelia burgdorferi lipoprotein recognized by monoclonal antibody LA7. Sequence analysis revealed an open reading frame encoding a 21,866-Da polypeptide (IpLA7). Comparison with other known proteins indicated sequence similarity between IpLA7 signal peptides and those of other prokaryotic lipoproteins, including the immunodominant B. burgdorferi outer surface proteins OspA, OspB, pC, and OspD. Both natural IpLA-7 and recombinant IpLA-7 could be biosynthetically labeled with [3H]palmitate. Upon solubilization of intact B. burgdorferi with the nonionic detergent Triton X-114, IpLA7 was extracted together with other lipoproteins into the detergent phase. Indirect immunolabeling studies indicated that the epitope recognized by monoclonal antibody LA7 is mainly located in the periplasmic space. Two-dimensional gel electrophoresis and immunoblotting confirmed the calculated acidic pI of 5.7 for IpLA-7. The LA7 gene was shown to be species specific and to be located on the linear chromosome of B. burgdorferi. The analysis of 40 individual spirochetal isolates on the basis of restriction fragment length polymorphisms revealed considerable genotypic heterogeneity of LA7 corresponding to that previously found for ospA. Native IpLA-7 and recombinant IpLA-7 were recognized by immune sera from infected mice as well as some human sera derived from infected but healthy donors and may thus prove useful as an additional marker for the serodiagnosis of Lyme disease.

Distinct patterns of protective antibodies are generated against Borrelia burgdorferi in mice experimentally inoculated with high and low doses of antigen

We have studied the development of clinical arthritis and the generation of protective antibodies in two normal, inbred strains of mice either infected by ticks or experimentally (subcutaneous) inoculated with increasing numbers of Borrelia burgdorferi organisms. AKR/N mice developed only mild and DBA/2 mice only marginal clinical arthritis irrespective of the route of infection or the numbers of spirochetes (10-10(8)) inoculated. In contrast, immunodeficient SCID mice developed severe chronic arthritis under similar conditions, but with a delayed onset at lower numbers of needle-inoculated spirochetes or after tick bite. AKR/N and DBA/2 mice inoculated with either 10(4) (and fewer) B. burgdorferi organisms or via experimentally infected ticks generated antibodies with specificities for a variety of B. burgdorferi antigens except those to the outer surface proteins A and B (OspA, OspB). In contrast, mice inoculated with more than 10(4) spirochetes (10(5)-10(8)) developed in addition antibodies to OspA and OspB. Most notably, all three types of immune sera taken from DBA/2 mice showed similar capacities to confer protection on SCID mice against subsequent challenge with viable B. burgdorferi organisms. The data not only demonstrate that the quality of humoral immune responses to B. burgdorferi in mice is determined by the antigenic load, they also indicate the existence of further protective antibodies with specificities distinct from OspA and OspB.

Mode of inoculation of the Lyme disease agent Borrelia burgdorferi influences infection and immune responses in inbred strains of mice

Mice were infected with Borrelia burgdorferi by infection via Ixodes ricinus and experimental inoculation to determine whether transmission rates of spirochetes and antibody responses are influenced. Mice infected by the natural route were substantially more infective for ticks; two- to sixfold more tick larvae were positive for B. burgdorferi than those fed on experimentally inoculated mice. In natural infection, spirochetemia may be greater or spirochetes may be more accessible for transmission. Thus, this form of xenodiagnosis could be used to determine levels of spirochetes in the vertebrate host. Similar levels of antibody were present in all mice; however, those infected by the natural route lacked antibodies to outer surface proteins (Osp) A and B. The small antigen dose given through a tick bite may not have been sufficient to induce rapid OspA or OspB antibodies, thereby allowing the later development of higher levels of spirochetemia.

Immune sera to individual Borrelia burgdorferi isolates or recombinant OspA thereof protect SCID mice against infection with homologous strains but only partially or not at all against those of different OspA/OspB genotype

The outer surface proteins OspA and OspB of Borrelia burgdorferi have recently been demonstrated to be major target proteins for protective antibodies in mice against infection with the homologous spirochaetal strain. However, it has become clear from a variety of studies that B. burgdorferi isolates of different geographical origin and/or sources are heterogeneous and that they can be divided into at least six subgroups according to their distinct OspA/OspB genotypes. In order to analyse cross-protection between these subgroups we have now generated immune sera to various isolates of B. burgdorferi with different OspA/OspB genotypes. We show that passive immunization with antisera specific for whole spirochaetes or recombinant OspA of one spirochaetal isolate protects severe combined immunodeficiency mice against infection with strains of the corresponding OspA/OspB genotype but only partially or not at all against infection with isolates expressing distinct OspA/OspB genotypes. The incomplete protection mediated by individual antisera against independent isolates of B. burgdorferi suggests that an effective subunit vaccine against Lyme disease should consist of a mixture of OspA structures covering the heterogeneity of this protein within the species B. burgdorferi.

Evaluation of genetic divergence among Borrelia burgdorferi isolates by use of OspA, fla, HSP60, and HSP70 gene probes

In order to assess the genetic variation of immunologically relevant structures among isolates of the Lyme disease spirochete, Borrelia burgdorferi, three chromosomal genes encoding flagellin (fla) and the heat shock proteins HSP60 and HSP70, as well as the plasmid gene encoding outer surface protein A (OspA), from 55 different European and North American strains obtained from ticks and mammal hosts have been investigated by restriction fragment length polymorphisms (RFLPs). RFLPs of fla and the HSP60 and HSP70 genes revealed two distinct banding patterns (A and B) for each of the three genes and allowed the definition of four genomic groups [AAA, BBB, BBA, and B(A/B)A] for the three chromosomal genes. On the other hand, RFLPs of the OspA gene revealed six distinct banding patterns (types I to VI) making up six independent genomic groups for the plasmid-encoded gene. Furthermore, we have sequenced the chromosomal HSP60 gene from B. burgdorferi ZS7 and the plasmid-encoded OspA gene from two strains, ZQ1 and 19857. Alignment of the deduced HSP60 amino acid sequence from B. burgdorferi ZS7 (genomic group AAA) to a previously published HSP60 sequence derived from strain ACA-1, which according to the proposed classification is in a different genomic group (BBA), revealed a sequence identity of > 99%. Similar alignments of the OspA sequence of strain ZQ1 to those of other isolates that were published previously revealed sequence identities of between 70 and 94% among strains of distinct OspA genomic groups. These data indicate the existence of a restricted number of species-specific subgroups and clearly show that genotypic variation is much more pronounced for the OspA gene than for fla and the HSP60 and HSP70 genes. A phylogenetic tree constructed on the basis of distance matrix analyses of 12 OspA sequences supports the proposed classification of genomic groups of B. burgdorferi.

Coiling phagocytosis is the preferential phagocytic mechanism for Borrelia burgdorferi

The uptake mechanism for the spirochete Borrelia burgdorferi, the causative agent of Lyme disease, was investigated by electron microscopy for human and murine phagocytes. Spirochetes of both a low- and a high-passage strain were preferentially internalized by coiling rather than by conventional phagocytosis. The spirochetes engulfed by coiling phagocytosis were found to disintegrate in an organelle exclusion zone without evident participation of lysosomes. Preincubation of B. burgdorferi with monoclonal antibody to the spirochetal OspA enhanced phagocytosis in general but did not consistently influence the uptake mechanism. Quantitative and kinetic differences concerning the phagocytic rate and mechanism were evident between cells from different lineages, different human individuals, and mice and humans. In general, when few phagocytes participated in spirochete uptake, the active cells displayed a high ratio of coiling versus conventional phagocytosis. These results suggest that coiling phagocytosis of B. burgdorferi plays a critical role in the control of spirochetal infection. More detailed studies on the molecular basis of this phagocytic mechanism may lead to new insights into the pathogenesis of Lyme borreliosis, a disease which is frequently characterized by the host's inability to eliminate the pathogenic spirochete.

Cellular immune reactivity to recombinant OspA and flagellin from Borrelia burgdorferi in patients with Lyme borreliosis. Complexity of humoral and cellular immune responses

Patients with Lyme borreliosis (LB) usually develop a vigorous T cell response against the causative pathogen Borrelia burgdorferi, but little is known about the antigens recognized in the cellular response. Therefore, T cell reactivities against whole bacteria, recombinant 31-kD (outer surface protein A, [OspA]), and 41-kD proteins (flagellin) from B. burgdorferi were studied in patients with LB, non-LB patients, and healthy donors. In parallel, specific antibodies were determined by Western blot analysis. Virtually all patients with LB exhibited marked cellular responses to whole B. burgdorferi, which were significantly elevated compared with the control groups in both early and late disease stages. However, analyses using the purified antigens OspA and flagellin revealed considerable heterogeneity in the cellular reactivities among individuals as well as variations during the course of infection. T cell responses to OspA were significantly increased in patients with early LB compared with both control groups whereas in late-stage disease responses only exceeded those of non-LB patients and were not different from normal donors. Cellular immune reactivities to flagellin were significantly higher only in early LB compared with both control groups. Reciprocally, several control subjects demonstrated marked cellular responses to OspA and flagellin, suggesting that reactions to these proteins may not always be related to LB. T cell reactivity did not correlate well with the presence of specific antibodies. Almost all seropositive patients in both early and late stage LB had serum antibodies against flagellin, but antibodies to OspA were detectable only in a subset of late LB sera. These data demonstrate the complexity of the humoral and the cellular immune responses to components of B. burgdorferi.

Myositis in mice inoculated with Borrelia burgdorferi

The authors describe the appearance of myositis in immunocompetent and immunodeficient mice after subcutaneous inoculation with Borrelia burgdorferi by histology and immunohistology. Experimental infection of mice 1) causes inflammation of striated but not smooth muscles, 2) affects the entire musculoskeletal system, and 3) is characterized by perivascular and interfacicular infiltration of mononuclear leukocytes in the striated muscle leading to necrosis as well as disruption of muscle fibers. The lesions found in striated muscle specimens were most pronounced in immunodeficient (SCID), less severe in T-cell-deficient nu/nu (BALB/c, C57BL/6) and marginal to moderate or almost not present in immunocompetent AKR/N and C.B-17 mice, respectively.

Experimental Borrelia burgdorferi infection in inbred mouse strains: antibody response and association of H-2 genes with resistance and susceptibility to development of arthritis

We have investigated the specific humoral immune response and its correlation to the development of disease after experimental inoculation of B. burgdorferi in different inbred strains of mice. All mouse strains tested showed high levels of specific IgM antibodies during the initial 10 days of infection. Specific IgG antibodies predominantly of the IgG2a, IgG2b and IgG3 isotypes were found in increasing amounts by 14 days post infection. Antibody titers peaked at days 65 and 110. Particularly low titers of specific IgM and/or IgG antibodies were detected in sera of AKR/N and B10.BR mice. Antibodies specific for numerous B. burgdorferi antigens including the outer surface proteins A (31 kDa) and B (34 kDa) and a protein(s) of molecular mass of approximately 40 kDa, most probably 41 kDa (flagellin) and/or 39 kDa (p39), were induced in all inbred mouse strains within 2 weeks inoculation albeit in varying concentrations. Later during infection, the patterns of antibody specificities were much more complex. With regard to development of disease all strains of mice tested fall into three groups: (a) mice of H-2k haplotype (AKR/N, C3H/HeJ, C3H/HeN, B10.BR) developed a chronic progressive arthritis in the tibiotarsal joints, (b) mice of H-2 haplotypes, H-2b (C57BL/6), H-2j (B10.WB), H-2r (B10.R111) and H-2s (B10.S) developed arthritis of variable duration and intensity which was not progressive and (c) mice of H-2d haplotype (BALB/c, DBA/2, C.B-17, B10.D2, Cal.20), irrespective of their background genes or Igh allotype, showed no clinical signs of arthritis at any time point following inoculation of B. burgdorferi organisms. The finding of similar patterns of apparently protective antibodies in all mouse strains tested together with the striking association between the H-2d haplotype and resistance, and between the H-2k haplotype and the occurrence of B. burgdorferi-induced arthritis suggest a critical role of T cells in the development of the disease in mice.

Recombinant outer surface protein a from Borrelia burgdorferi induces antibodies protective against spirochetal infection in mice

The outer surface protein A (OspA) of Borrelia burgdorferi was isolated in its native form from strains ZS7 and B31 and as a recombinant protein from strain ZS7. Amino acid sequence analysis of internal peptides of native OspA (strain ZS7) revealed identity with the sequence deduced from the OspA gene. Repeated immunization of C57BL/6 and C.B-17 mice with any of the three OspA structures resulted in the generation of monospecific hyperimmune sera reactive with both native and recombinant OspA. Upon transfer of immune sera specific for either native OspA (strain B31) or recombinant OspA (strain ZS7) but not of those reactive with the recombinant 41-kDa flagellin-associated antigen, severe combined immunodeficient (SCID) mice were completely protected against infection with strain ZS7. The finding that monoclonal antibodies to OspA and to OspB but not to non-outer surface spirochetal structures such as flagellin, p20, p65, and p70 conferred protection in SCID mice makes OspA (and possibly OspB) a promising candidate vaccine against Lyme disease.

A mouse model for Borrelia burgdorferi infection: pathogenesis, immune response and protection

Viable Borrelia burgdorferi (B. burgdorferi) organisms induce a chronic infection associated with arthritis, carditis and hepatitis in severe combined immunodeficiency (scid) mice but not in most of the adult mice from the various immunocompetent inbred strains tested. Furthermore, we have found that experimental inoculation of normal mice with B. burgdorferi organisms leads to the generation of antibodies and T cells specific for various spirochetal antigens including the outer surface proteins A and B (OspA, OspB) as well as flagellin. The assumption of a protective role of the immune response during B. burgdorferi infection in mice is supported by our recent findings that passively transferred B. burgdorferi-specific immune mouse sera as well as monoclonal antibodies to OspA are able to prevent the development of the disease in scid mice. We show now that purified OspA protein both in its native and recombinant form is immunogenic and that the antibodies generated are able to confer protection to scid mice against B. burgdorferi infection.

[Borrelia burgdorferi infection. II. Aspects of basic research, new approaches to diagnosis and therapy]

In this review article, current thinking about the infection caused by Borrelia burgdorferi is presented. The problems associated with diagnosis and treatment of Borrelia burgdorferi infection are pointed out. A series of monoclonal antibodies recognizing Borrelia burgdorferi-associated antigens is presented. In collaborative research projects these antibodies have been used for molecular biological (cloning and sequencing of Borrelia burgdorferi antigens) and immunological (protection experiments by passive transfer of monoclonal antibodies in an animal model) experiments. Taken together, these studies disclosed new aspects for diagnosis and therapy of the Borrelia burgdorferi infection. In this second part of the review article the above-mentioned molecular biological and protection experiments are summarized.

A mouse model for Borrelia burgdorferi infection: approach to a vaccine against Lyme disease

Lyme disease is the most common vector-transmitted illness in the USA and Europe. The pathogen, Borrelia burgdorferi, causes a complex spectrum of disease that affects the skin, joints, nervous system and heart. Patients in the early stages of the disease can often be successfully treated with antibiotics but this becomes less reliable as the disease progresses. The specific immune responses that are detectable in patients with Lyme disease are not sufficient to protect against illness; a vaccine against the infectious agent is, therefore, desirable. In this article Markus M. Simon and colleagues present a mouse model of Borrelia burgdorferi infection. Their work suggests that the outer surface protein A (OspA) of Borrelia burgdorferi may be a suitable vaccine candidate.

[Borrelia burgdorferi infection. I. Aspects of basic research, current approach for diagnosis and therapy]

In this review article the current concepts on the infection caused by Borrelia burgdorferi are presented. The problems associated with the diagnosis and therapy of the Borrelia burgdorferi infection are pointed out. A series of monoclonal antibodies recognizing Borrelia burgdorferi-associated antigens is presented. In collaborative research projects these antibodies were used for molecular biological (cloning and sequencing of Borrelia burgdorferi antigens) and immunological (protection experiments by passive transfer of monoclonal antibodies in an animal model) experiments. Taken together, these studies disclosed new aspects of the diagnosis and therapy of Borrelia burgdorferi infection. In the first part of the review article the immunochemical characterization of the aforementioned antibodies and their use for antigen detection by immunohistochemistry is described.

Characterization of Borrelia burgdorferi associated antigens by monoclonal antibodies

In this paper, we present a series of murine mAb recognizing B. burgdorferi antigens. The antibodies were characterized by immuno-blotting and immuno-fluorescence studies using isolates of B. burgdorferi from North America and Europe, respectively. Moreover, reactivity of the antibodies with recombinant B. burgdorferi flagellin and OspA was studied. The results suggest these anti-B. burgdorferi mAb as valuable tools for the serological analysis of B. burgdorferi isolates and for affinity-purification of the respective proteins. Moreover, these mAb appear suitable to classify antigenic variants of B. burgdorferi and to study the protective capacity of antibodies in a murine model for B. burgdorferi infection.

Lyme borreliosis in the severe combined immunodeficiency (scid) mouse manifests predominantly in the joints, heart, and liver

The authors describe the histopathologic evolution of Lyme disease in severe combined immunodeficiency (scid) and normal C.B-17 and C57BL/6 mice inoculated with Borrelia burgdorferi. Starting on day 7 after inoculation, all scid mice infected subcutaneously in the tail with a low-passage European tick isolate of B. burgdorferi had clinical evidence of arthritis characterized by reddening and swelling of tibiotarsal joints. Later on, other joints, ie, metatarsal and ulnacarpal joints were also affected. The infection of scid mice resulted in a persistent spirochetemia and the development of a multisystem disease with chronic progressive inflammation of joints, heart, and liver. Major histopathologic alterations included 1) severe joint lesions, characterized by the presence of hyperplastic inflamed synovial lining cells associated with the erosion and destruction of cartilage and/or bone; 2) pancarditis with infiltrations of mononuclear cells in the endocardium, myocardium, and pericardium; and 3) hepatitis with mononuclear cell infiltrations confined to the portal field and central vein, granulomatous reactions, and eventually the development of liver fibrosis. In addition, smaller more confined lesions were found in kidneys, lung, brain, and striated muscle. The inflammatory infiltrates in the various organs were associated mostly with Mac-1+ cells, largely monocytes and macrophages, as well as some polymorphonuclear leukocytes, but not B and T lymphocytes. Infective spirochetes could be readily isolated from blood and joints and were found at the site of inoculum and the myocardium. In contrast, subcutaneous inoculation of normal C.B-17 or C57BL/6 mice with spirochetes in general did not result in clinical signs of arthritis. Only 10% to 20% of the C57BL/6 mice, but none of the C.B-17 mice, showed clinical evidence of oligoarthritis, which appeared not before day 36 after inoculation. In general, the infection of normal mice resulted in minimal lesions in various organs, and no spirochetes could be visualized or reisolated from their tissues. The data demonstrate that Lyme borreliosis may develop in mice in the absence of detectable specific B and T cells and thus suggest an immunologic control of the disease in this species. The scid mouse model therefore can be used to define the components of the immune system responsible for the suppression and/or the progression of the disease.

Lyme carditis in immunodeficient mice during experimental infection of Borrelia burgdorferi

Recently, we described the severe combined immunodeficiency (scid) mouse as a laboratory model for B. burgdorferi infection. Scid mice inoculated with the virulent low-passage tick isolate Borrelia burgdorferi ZS7 developed a severe pancarditis involving endocardium, myocardium and epicardium in the absence of functional B- or T-cells. Soon after inoculation perivascular infiltration was observed, later diffuse infiltration of the interstitium of the subendocardial and subepicardial areas was seen. The infiltrate was mainly mononuclear and predominantly composed of Mac-1+ cells. Concomitantly, fibroblast proliferation and augmented collagen deposition occurred in the interstitium. This was associated with the presence of B. burgdorferi organisms. The histopathological and ultrastructural findings observed in scid mice resemble those observed in human Lyme carditis. The data emphasize the suitability of the scid mouse as a model in which to study the role of the immune system in the pathogenesis of Lyme carditis.

Monoclonal antibodies specific for the outer surface protein A (OspA) of Borrelia burgdorferi prevent Lyme borreliosis in severe combined immunodeficiency (scid) mice

We have recently shown that viable Borrelia burgdorferi organisms induce a chronic infection associated with arthritis and carditis in severe combined immunodeficiency (scid) mice but not in immunocompetent mice. The disease is similar to that found in patients suffering from Lyme disease. We now show that B. burgdorferi-specific immune mouse sera as well as a monoclonal antibody to the spirochetal outer surface antigen A (31 kDa) but not monoclonal antibodies specific for the 41-kDa antigenic component of the periplasmic flagella are able to prevent (or mitigate) the development of the disease in scid mice when passively transferred at the time of the bacterial inoculation. The identification of a B. burgdorferi-associated protective antigen suggests that the corresponding spirochetal protein should be tested as a vaccine against Lyme disease.