Intrathecal immune response and virus-specific immunoglobulin M antibodies in laboratory diagnosis of acute poliomyelitis.

The intrathecal immune response in 114 patients with clinically diagnosed acute poliomyelitis was studied by measuring poliovirus-specific immunoglobulin M (IgM) antibodies in cerebrospinal fluid (CSF) by a mu-capture immunoassay and by assessing the ratio between levels of poliovirus-neutralizing antibodies in serum and CSF. Fecal specimens were used for attempts to isolate the causative agents. Eighty-five percent of CSF specimens collected during the first 15 days of disease contained virus-specific IgM antibodies. Forty-five of 48 tested children (94%) also showed virus-specific IgM responses in their sera. Later on, the antibody levels decreased, and positive results after 30 days of onset of paralytic symptoms were rare. If the presence of poliovirus-specific IgM antibodies in the CSF was considered diagnostic, more cases were confirmed by this test than by virus isolation. A relative increase in poliovirus-neutralizing antibodies in the CSF was observed in about one-third of the cases; in all but three cases the increase was observed together with the presence of virus-specific IgM antibodies. A systemic virus-specific response can be seen and poliovirus can be isolated from a subclinically infected individual suffering from a concomitant poliomyelitis-like disease, while positive results by the two methods demonstrating an intrathecal immune response are likely to indicate a true causal relationship between infection and disease. Demonstration of poliovirus-specific IgM antibodies in the CSF thus appears to be a sensitive and specific method for laboratory confirmation of clinically diagnosed poliomyelitis.

An immunodominant N-terminal region of VP1 protein of poliovirion that is buried in crystal structure can be exposed in solution.

According to previous X-ray crystallographic analyses of poliovirus structure, the amino terminal region of the capsid protein VP1 is inside the capsid shell. We have found that antibodies to synthetic peptides derived from an immunodominant part of this region readily precipitate intact infectious virions, indicating that in solution, the virus can assume a conformation that is partially different from that seen in the crystal structure. We propose that this part of VP1 is alternating between two conformations.