Experimental transmission of the Lyme disease spirochete to rabbits

Complement-mediated killing of Borrelia burgdorferi by nonimmune sera from sika deer

Various species of cervid deer are the preferred hosts for adult, black-legged ticks (Ixodes scapularis and Ixodes pacificus) in the United States. Although frequently exposed to the agent of Lyme disease (Borrelia burgdorferi), these animals, for the most part, are incompetent as transmission reservoirs. We examined the borreliacidal activity of normal and B. burgdorferi-immune sera from sika deer (Cervus nippon) maintained in a laboratory setting and compared it to that of similar sera from reservoir-competent mice and rabbits. All normal deer sera (NDS) tested killed > 90% of B. burgdorferi cells. In contrast, normal mouse and rabbit sera killed < or = 22% of the Borrelia. Anti-B. burgdorferi antibodies could not be detected in any normal sera by indirect fluorescent antibody assay (IFA). Sera collected from deer 6 wk after exposure to B. burgdorferi by tick feeding exhibited IFA titers of 1:256, whereas sera from mice and rabbits similarly exposed had titers of > 1:1,024. Heat treatment (56 C, 30 min) of NDS reduced borreliacidal activity, with < 20% of the B. burgdorferi cells killed, suggesting complement-mediated killing. The chelators EGTA and EDTA were used to block the classical or both the classical and alternative complement pathways, respectively. Addition of 10 mM EGTA to NDS had a negligible effect on borreliacidal activity, with > 90% of the cells killed. Addition of 10 mM EDTA reduced the killing to approximately 30%, whereas the addition of Mg2+ (10 mM) restored borreliacidal activity to NDS. The addition of zymosan A, an activator of the alternative pathway, increased the survival of B. burgdorferi cells to approximately 80% in NDS. These data suggest that the alternative complement activation pathway plays a major role in the borreliacidal activity of NDS. Additionally, 10 mM EGTA had almost no effect on the killing activity of B. burgdorferi-exposed deer sera, suggesting that the classical pathway is not involved in Borrelia killing, even in sera from B. burgdorferi-exposed deer.

Lyme borreliosis: host responses to Borrelia burgdorferi

The chronic inflammatory condition that develops after infection by B. burgdorferi is a complex process resulting from host responses to a limited number of organisms. Amplification mechanisms driven by potent proinflammatory molecules, i.e., IL-1, may explain the vigorous response to a paucity of organisms. Spirochete dissemination to distant locations involves adherence to and penetration across endothelium and may be facilitated by host responses that increase vessel permeability. The apparent lack of tissue tropism in Lyme disease is reflected in the organism's ability to adhere to different eucaryotic cell types in vitro and the wide distribution of B. burgdorferi in various organs of infected humans and experimentally infected animals. While phagocytosis and complement activation have been observed in vitro, the specific immune response that develops in humans is inefficient in eradicating the organisms, which may possess some mechanism(s) to evade this response. There is significant evidence for host autoreactivity based on antigenic cross-reactivity between the 41-kDa flagellar subunit and stress proteins of the spirochetes and endogenous host cell components. Although the outer surface proteins appear to be suitable candidates as targets for vaccination in animal studies, fundamental differences in the immune response to spirochetal components may preclude their use in humans.

Aspects of the diagnosis of Lyme borreliosis

Attempts were made to culture spirochetes from the cerebrospinal fluid of 105 patients with suspected Lyme borreliosis with neurological complications. At the final evaluation, only 38 patients fulfilled the criteria of neuroborreliosis. Spirochetes were cultured from the cerebrospinal fluid of four of these patients. All four had pleocytosis in their cerebrospinal fluid and a history of neurological symptoms of only four to ten days. Two had no detectable antibodies in their cerebrospinal fluid against any of the isolated spirochetes, neither when tested with an ELISA nor by Western blot. A distinctly stronger antibody reaction to the homologous isolate than to the heterologous isolates was found in serum and cerebrospinal fluid from one patient. The cells of the isolates were morphologically similar and showed a very similar protein pattern when analyzed by SDS-PAGE. Cells of all isolates reacted with the monoclonal antibodies H5332 and H9724, which also react with Borrelia burgdorferi isolate B31, the type species. One isolate lost a major protein of 23 kD after subcultivation for four months. We conclude that isolation of spirochetes from cerebrospinal fluid is not suitable as a routine method but might prove successful in clinically selected cases of Lyme borreliosis. The patient antibody response to spirochetal components was analyzed with Western blot. Antibodies to low-molecular components including a major protein with a molecular weight of 21-23 kD, and to a 41-kD major flagellar protein, were the first to appear in serum and in CSF samples. No single band in the immunoblots was found to be specific. By requiring a 41 kD band together with at least one low-molecular band for a positive immunoblot, 53 of 68 (78%) patients with neuroborreliosis had positive IgM and/or IgG serum immunoblots by visual reading of coded material. Western blot was more sensitive than ELISA based on a sonicate antigen which identified 40 of the 68 (59%) patient samples as positive, but not significantly more sensitive than ELISA based on a purified flagellum antigen which identified 50 of 68 (74%). Western blot tended to be more sensitive than the flagellum ELISA regarding sera from patients with neurological symptoms of 2 weeks or shorter duration. However, there was a tendency towards a lower specificity regarding the serological diagnosis of current Lyme borreliosis by Western blot than by sonicate and flagellum ELISAs.(ABSTRACT TRUNCATED AT 400 WORDS)

Laboratory aspects of Lyme borreliosis

Lyme borreliosis (Lyme disease), a common tick-borne disorder of people and domestic animals in North America and Europe, is caused by the spirochete Borrelia burgdorferi. Following the discovery and initial propagation of this agent in 1981 came revelations that other tick-associated infectious disorders are but different forms of Lyme borreliosis. A challenge for the clinician and microbiology laboratory is confirmation that a skin rash, a chronic meningitis, an episode of myocarditis, or an arthritic joint is the consequence of B. burgdorferi infection. The diagnosis of Lyme borreliosis may be established by (i) directly observing the spirochete in host fluid or tissue, (ii) recovering the etiologic spirochete from the patient in culture medium or indirectly through inoculation of laboratory animals, or (iii) carrying out serologic tests with the patient's serum or cerebrospinal fluid. The last method, while lacking in discriminatory power, is the most efficacious diagnostic assay for most laboratories at present.

An animal model for Lyme arthritis

A model of Lyme arthritis has been developed in laboratory rats. Intraperitoneal inoculation of a low-passage tick isolate of B. burgdorferi into neonatal and weanling LEW/N rats resulted in multisystemic infection and arthritis. Spirochetes were isolated from blood, liver, kidney, spleen, brain, and joints of inoculated rats. Arthritis, associated with the presence of spirochetes, developed in multiple joints by day 14 and persisted through day 90 after inoculation. Arthritic lesions resembled those found in human Lyme disease lesions. Lesions were not found in other organs, although spirochetes were present. Neonatal F344 and SD rats were also susceptible to infection and induction of arthritis. Three different isolates of B. burgdorferi were shown to be pathogenic. Pathogenicity of one isolate was retained after at least 11 in vitro passages. Formalin-killed spirochetes were not pathogenic. Other features of the Lyme disease complex have yet to be seen in the rat, but long-term studies are required to completely define the rat model. This highly reproducible model should allow in-depth studies on the pathogenetic mechanisms of this important human disease.

Biology of Borrelia species

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