[Immunologic diagnosis of central nervous system viral infection]

Immunologic diagnosis of central nervous system viral infection requires paired sera, obtained at the onset of symptoms and in the convalescent period. Titers of antibodies against a particular virus in these samples should be obtained under the same conditions. As a screening test, the complement fixation or hemagglutination method is used. On the other hand, the neutralization, the enzyme-linked immunosorbent assay (ELISA) or the Western blot method is used as a confirmatory test. An antibody capture ELISA is especially effective for detecting viral antibody in the cerebrospinal fluid. Although a four-fold or greater increase in a viral antibody titer is serologically considered indicative of active viral infection, it may be clinically irrelevant. Accordingly, clinical correlation should always be sought when interpreting the results of the viral titer assay.