Tick-borne encephalitis: a simple method for detection of antibody production in the brain.

Antibodies found in c.s.f. of patients with TBE are usually produced in the CNS itself, although their presence might also be due to a leak in the blood brain barrier. In the case of local antibody production the ratio of the TBE specific IgM or IgG to the total immunoglobulin is relatively high in c.s.f., whereas in case of a leak this ratio is lower and corresponds to that of the serum. Local antibody production in the brain can therefore be assumed, if the ratio is higher in c.s.f. than in serum. It is possible to determine this ratio in an anti-mu or anti-gamma capturing antibody ELISA, provided that the concentration of capturing antibodies represents the limiting factor of the test system. Under these conditions the absorbance values obtained are a direct reflection of the TBE reactive to nonreactive antibody ratio, since they compet for the limited binding sites presented on the solid phase. Higher extinction values of c.s.f. compared to that of serum are therefore an indication for local antibody production in the brain. Using the method described, differences were found in the production of IgM and IgG antibodies against TBE in the CNS from patients with different clinical history.