Immunoglobulin abnormalities in the cerebrospinal fluid during bacterial meningitis

11 patients with bacterial meningitis, examined during the course of the disease for immunoglobulin (Ig) abnormalities in the cerebrospinal fluid (CSF), all had an increased CSF IgM index equal to (CSF/serum IgM):(CSF/serum albumin), indicating intrathecal IgM production. Seven patients had a slightly increased CSF IgG index, and 7 a slightly increased IgA index. Six of the 11 patients had an increased IgM index in the presence of normal indices for IgG and IgA. Follow-up revealed the return of these values to normal. Four patients had identical oligoclonal IgG bands in the CSF and serum, probably representing a systemic immune response, but in only one case were oligoclonal bands suggestive of intrathecal IgG production found. No oligoclonal IgA response was demonstrable in the 4 patients examined. Antigen-immunofixation or antigen-absorption studies revealed evidence of a specific, intrathecal IgG antibody response in only 2 patients, while a search for IgG antibodies against aetiologically unrelated bacterial and viral antigens was negative. With the exception of IgM production, therefore, a humoral intrathecal immune response is less common in bacterial than in aseptic meningitis.