Background/Purpose

Borrelia burgdorferi-induced autoimmunity in affected joints has been hypothesized to be a contributing factor to antibiotic-refractory Lyme arthritis (ARLA).  Our prior study, which combined proteomics and translational research, identified endothelial cell growth factor (ECGF) as the first known target of  T and B cell responses in ~20% of patients with antibiotic-refractory or antibiotic-responsive arthritis and in ~10% of patients with erythema migrans (EM), the initial skin lesion of the disorder. Using this same approach, we identified apolipoprotein B (ApoB) as another novel autoantigen in Lyme disease.

Methods

HLA-DR presented self-peptides were isolated from ALRA patients’ synovia, identified by tandem mass spectrometry, synthesized, and tested for reactivity with the matching patient’s PBMC using an IFN-γ ELISpot assay.  Immunoreactive peptides and their full-length source proteins were then tested for T and B cell reactivity using large numbers of patient and control cells and sera.  Samples from patients with antibiotic-responsive arthritis were seen prior to antibiotic therapy, when the infection was still active, whereas those from patients with antibiotic-refractory arthritis were collected after antibiotics, during the presumed autoimmune phase of the illness. Antibody responses were quantified by ELISA.

Results

From the synovial tissue of one ALRA patient, 141 non-redundant HLA-DR-presented self-peptides were identified and tested. One peptide derived from ApoB caused significant secretion of IFN-γ by ELISpot. Additional testing of 25 patients showed ~10-30% patients with early or late manifestations of Lyme disease had T cell responses to ApoB. 

To look for linked T and B cell responses, patients’ serum samples were also tested for anti-ApoB IgG antibodies.  By definition, none of the 55 healthy control subjects had a positive response (defined as >3 SD above the mean value in these subjects) (Figure).  In comparison, 5% of patients with EM and 12% each of patients with responsive or refractory arthritis had positive responses for anti-ApoB IgG autoantibodies. Compared with the EM group, the values were significantly higher in both arthritis groups (P<0.0001), particularly in those with responsive arthritis, a group still actively infected. 

Conclusion

We report for the first time that ApoB is a target of T and B cell responses in a subset of patients with Lyme disease. Although the molecular mechanisms are not yet known, B. burgdorferi, an organism with sequences for >100 lipoproteins and multiple membrane glycolipids containing cholesterol, may contribute directly to the development of this autoimmune response.  As with reactivity to ECGF, autoantibody responses to ApoB seem to occur as part of the immune response to the infection, whereas additional factors, such as immune dysregulation, are also required for refractory arthritis.