[Immunology and diagnostic test results in Lyme borreliosis]

Borrelia burgdorferi (B. burgdorferi), the etiologic agent of Lyme borreliosis, shows both a variety of outer surface proteins with molecular weights between 16 and 100 kiloDalton (kD) and a 41 kD flagellar protein, which induce the immunologic response. Lipopolysaccharides, another constituent of the bacterial capsule, are responsible for the inflammatory reaction, constitutional symptoms and for the Jarisch-Herxheimer reaction. First a vigorous T-cell immune response develops, followed later by a more slowly evolving humoral B-cell immune response. The delayed onset of the humoral immune response may explain why antibodies against B. burgdorferi could not be detected early in the course of the disease. But the antibody titers increase with duration of the illness. The humoral response shows the usual pattern of IgM appearing first, followed by IgG and IgA. The IgM titer normalizes after recovery while the IgG titer could persist over years or decades. It is hardly possible to detect B. burgdorferi microscopically or by cultivation from blood, joint or cerebrospinal fluid. For routine diagnosis the fluorescent antibody staining and the ELISA methods are available which detect IgM or IgG antibodies against B. burgdorferi. But the sensitivity and specificity of these tests are still unsatisfactory. Other methods such as the ELISA-capture method, complement binding reaction, passive hemagglutination or the polymerase chain reaction are not yet established for routine purposes. Western blot analysis did not yield an essential diagnostic advantage but may be helpful in long term observation or in special cases. The measurement of the cellular immune response by T-cell proliferation tests remains controversial. First of all Lyme borreliosis has to be diagnosed by clinical findings and by elimination through differential diagnosis. An elevated antibody titer or a positive T-cell proliferation test may confirm the diagnosis but cannot prove it. Without consistent clinical findings they are of no practical significance. Some general guidelines for interpretation of laboratory results are given.