We report sequestration of specific IgM anti-Borrelia burgdorferi (Bb) and Bb antigens within immune complexes (ICs) isolated from serum of patients with
Lyme disease (LD). The relative enrichment in specific IgM measured by ELISA was apparent, even after correcting for differences in total IgM concentration in serum versus ICs. Immunoblot demonstrated that ICs contained antibodies against specific Bb proteins, whereas reactivity was absent or significantly lessened in unprocessed serum. This is the first study to show ICs containing Bb antigen identified by immunoblot with anti-Bb monoclonal antibody. ICs may be a useful source of antigen and antibody for development of more-accurate testing for LD.