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An ospA frame shift, identified from DNA in Lyme arthritis synovial fluid, results in an outer surface protein A that
1Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520-8031, USA.
Abstract:
Passive immunization with murine or human Abs to outer surface protein A (OspA) can protect mice against Borrelia burgdorferi, but OspA Abs elicited during natural infection in mice or humans are unable to clear the spirochete from the infected host. To examine Ab binding by OspA during the course of human infection, we amplified the operon encoding full-length ospA and ospB from synovial fluids of a patient with chronic Lyme arthritis, the first such recoveries from human material, at four separate time points over 4.5 mo, and expressed OspA in Escherichia coli. OspA mAbs that passively protected mice from infection did not bind one of the expressed OspAs, because of a deletion in ospA that resulted in a frame shift and premature stop codon near the carboxyl terminus. However, expressed OspA from a later synovial fluid sample did not contain this deletion. Thus, although altered forms of OspA, which potentially can influence host immune effectiveness, do occur in the human host, they cannot be the only factors responsible for microbial persistence.
Insights
Antibodies to outer surface protein A (OspA) protect mice from Borrelia burgdorferi. However, altered OspA forms in chronic Lyme arthritis patients may explain why these antibodies fail to clear the bacteria in humans.
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Passive immunization with antibodies to outer surface protein A (OspA) confers protection against Borrelia burgdorferi in murine models.
- Antibodies generated during natural infection, however, are often insufficient to eradicate the spirochete in infected hosts, including humans.
Purpose of the Study:
- To investigate the binding characteristics of OspA antibodies during the course of human Borrelia burgdorferi infection.
- To analyze the genetic integrity of the ospA operon in synovial fluid from a patient with chronic Lyme arthritis.
Main Methods:
- Amplification of the ospA and ospB operons from synovial fluid samples collected over 4.5 months from a patient with chronic Lyme arthritis.
- Expression of OspA protein in Escherichia coli for antibody binding assays.
Main Results:
- OspA antibodies that conferred passive protection in mice failed to bind an OspA variant due to a deletion causing a frameshift and premature stop codon.
- A subsequent synovial fluid sample yielded an OspA variant lacking this deletion, indicating the occurrence of altered OspA forms during infection.
Conclusions:
- Altered forms of OspA, potentially impacting immune response effectiveness, can arise within the human host during Borrelia burgdorferi infection.
- These genetic variations in OspA are unlikely to be the sole reason for persistent microbial infection.