Borrelia burgdorferi is the causative agent of Lyme borreliosis, a mul
tisystem disorder, which can mimic numerous immune disorders and infla
mmatory diseases. Laboratory diagnosis of Borrelia infection relies on
immunodiagnostic assays, which, however, are hampered by unsatisfacto
ry specificity. The Westem blot technique.has been employed to analyze
the humoral immune response in Lyme borreliosis and is used as a sero
diagnostic confirmation test. The most important immunodominant protei
ns of Borrelia burgdorferi are the 94 kDa, 60 kDa, 41 kDa (flagellin),
34 kDa (Osp B), 31 kDa (Osp A), 30 kDa, 21 kDa (Osp C), and 17/18 kDa
proteins. Whereas the 60 kDa, 41 kDa, and 34 kDa constituents reveal
a marked cross-antigenicity with other spirochetes and even more dista
ntly related bacteria, antibodies against the 94 kDa, 31 kDa and 21 kD
a proteins are largely species-specific. The early immune response in
Lyme borreliosis is triggered mainly by the flagellin. In the later st
age a wide range of immunogenic proteins is involved, with the 94 kDa
antigen being the best marker for late immune response. If the Westem
blot is used for diagnostic purposes the differences between early and
late-stage immunogenicity of Borrelia proteins must be taken into acc
ount. Interpretation criteria for blot positivity in early-stage borre
liosis are primarily based on the presence of the 21 kDa band and the
semiquantitatively recorded intensity of the 41 kDa band. In the diagn
osis of late-stage infection, blot positivity relies on the presence o
f the 94 kDa, 39 kDa, 31 kDa, 30 kDa and 21 kDa bands.