Clinical relevance of polymerase chain reaction (PCR) assays and antigen-driven immunoblots for the diagnosis of neurological infectious diseases

Polymerase chain reaction assays are a powerful tool for detecting the presence of infectious genomes in the cerebrospinal fluid. Positive results always mean a current or pending infection of the central nervous system. Subacute (>7 days) or chronic infections induce an intrathecal humoral immune response and the appearance of oligoclonal IgG antibodies directed against the causal infectious agent. This local synthesis may be observed even in cases of severe systemic immunodeficiency. The use of polymerase chain reactions in combination with the detection of a specific intrathecal immune response should represent the most reliable strategy for the diagnosis of viral and chronic infections of the central nervous system. The authors describe their experience, using this approach, in herpetic encephalitis, acute and recurrent herpetic meningitis, varicella zoster-induced neurological diseases, cytomegalovirus encephalitis, progressive multifocal leukoencephalitis and tuberculous meningitis.

The intrathecal humoral immune response: laboratory analysis and clinical relevance

In normal conditions, albumin and immunoglobulin (Ig)G in the cerebrospinal fluid (CSF) originate from the blood, and there is no antibody production within the central nervous system. Up to 20% of CSF proteins are intrathecally synthesized, but the major fraction is blood-derived. The CSF/serum albumin quotient (QAlb) is the best marker of the blood-CSF barrier function. The corresponding immunoglobulin quotients (QIGG, QIGA, QIGM) are not linearly related to QAlb and their correlations are defined by an hyperbolic equation. This equation is used to discriminate between a blood-derived and a locally produced fraction of immunoglobulins in case of an intrathecal humoral immune response. The detection of CSF-specific oligoclonal IgG is more sensitive than the quantitative comparison between QIGG and QAlb. A further step is the determination of antibody indices and the detection of specific oligoclonal antibodies by antigen-driven immunoblots. CSF analysis remains a cornerstone for the diagnosis of various neurological disorders, including multiple sclerosis and infectious diseases of the central nervous system.

Expression of costimulatory molecules and cytokines in CSF and peripheral blood mononuclear cells from multiple sclerosis patients

We amplified the mRNA for cytokines in peripheral blood mononuclear cells (PBMC) and cerebrospinal fluid (CSF) cells from 18 multiple sclerosis (MS) patients and 21 other neurological patients, using the reverse transcription polymerase chain reaction (RT-PCR). Radioactive hybridization of the amplified DNA allowed quantitation of mRNA levels. Expression of tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma and interleukin (IL)-10 mRNA was elevated in CSF cells from MS patients. IFN-gamma and IL-10 mRNA levels were higher in MS patients than in other inflammatory neurological diseases. mRNA coding for transforming growth factor (TGF)-beta was detectable in the majority of cases, with higher expression in CSF cells of MS and other inflammatory neurological diseases than in noninflammatory controls, and higher expression in PBMC of MS patients than in all other cases. In many MS patients both proinflammatory and immunoregulatory cytokine messages were detected in the CSF compartment without correlation with the clinical activity of the disease. In contrast, mRNA for the costimulatory molecule B7.1 was only detected in the CSF cells of some MS patients, who showed clinical signs of acute relapse at the time of the spinal tap.

Detection of CSF-specific oligoclonal antibodies to recombinant JC virus VP1 in patients with progressive multifocal leukoencephalopathy

The intrathecal synthesis of antibodies against recombinant VP1, the major structural protein of JC virus (JCV), was studied in 18 patients with progressive multifocal leukoencephalopathy (PML) and in 31 patients with various neurological disorders. Two methods were used, the calculation of an antibody specific index (ASI) on one hand and an antigen-driven immunoblotting for the detection of oligoclonal antibodies on the other. Most PML patients displayed an elevated (> 1.5) ASI (78%) and anti-VP1 oligoclonal antibodies restricted to the cerebrospinal fluid (55%). Only two other patients (one case each of multiple sclerosis and of neuroborreliosis) also showed an intrathecal synthesis of anti-VP1 oligoclonal antibodies, likely as a result of a 'polyspecific' reaction within the central nervous system.

Analysis of tuberculous meningitis cases by an immunoblotting assay based on a mycobacterial antigen complex

Tuberculous meningitis cases were analyzed by an immunoblotting test based on Mycobacterium bovis BCG antigen complex A60. Anti-A60 immunoglobulin G (IgG) in cerebrospinal fluid (CSF) allowed early diagnosis, and concentrations decreased after recovery. In primary meningitis forms, anti-A60 IgGs were intrathecally synthesized and specific oligoclonal IgGs were present in CSF. In meningeal complications of pulmonary tuberculosis, there were matching titers of anti-A60 IgG in blood and CSF (mirror pattern). Correlation between CSF-restricted patterns and CSF pleocytosis was shown.

Intrathecal synthesis of anti-mycobacterial antibodies in patients with tuberculous meningitis. An immunoblotting study

Cerebrospinal fluid (CSF) and serum samples from eight patients with bacteriologically proven (6) or clinically suspected (2) tuberculous meningitis were tested for the presence of anti-mycobacterial IgG antibodies by an affinity-mediated immunoblot technique. This technique is based on agarose gel isoelectric focusing of paired CSF and serum samples diluted to the same IgG concentration, and transfer of the specific IgG antibodies onto mycobacterial antigen-loaded nitrocellulose sheets. An intrathecal synthesis of anti-mycobacterial oligoclonal IgG antibodies, often superimposed on diffuse polyclonal production was shown in all patients but not in patients with tension headache or other neurological disorders. Similar results were obtained when a purified mycobacterial antigen, A60, was used for coating the nitrocellulose sheets in place of a whole mycobacterial homogenate, indicating that A60 was a major immunogen. The number of anti-mycobacterial oligoclonal IgG bands increased with time, and persisted for years even in clinically cured patients. Some IgG bands had no detectable anti-mycobacterial activity, at least with the antigens preparations used in this study. The demonstration of such anti-mycobacterial IgG bands in the CSF could be a useful adjunct for the diagnosis of tuberculous meningitis, especially in the case of negative cultures.