HERPES-SIMPLEX ENCEPHALITIS - EARLY DIAGNOSIS AND IMMUNE ACTIVATION IN THE ACUTE STAGE AND DURING LONG-TERM FOLLOW-UP

From a series of in all 93 patients with herpes simplex encephalitis ( HSE), verified by biopsy and/or the demonstration of intrathecal synth esis of antibodies to the virus, cerebrospinal fluid (CSF) and serum s amples were analysed and compared with samples from 80 patients with n on-HSE, i.e. acute encephalitis of non-HSV origin (approximately 50% w ith other known aetiology, 50% of unknown origin) treated on the suspi cion of HSE but in whom no signs of intrathecal HSV antibody synthesis were found, and samples from an additional 42 patients with other ver ified or suspected diseases of the CNS. To improve the early non-invas ive diagnosis of HSE, a HSV IgG capture enzyme linked immunosorbent as say (ELISA) was developed to demonstrate intrathecal synthesis of anti bodies to the virus and the results were compared to those of the indi rect ELISA. The capture ELISA was found to be advantageous in detectin g the early antibody response and yielded more clear-cut results. No c orrection for damage to the blood-CSF barrier was needed and the metho d was therefore less labour-intensive than the indirect ELISA. Further more, a polymerase chain reaction (PCR) assay, with two ''nested'' pri mer pairs selected in the glycoprotein D gene of HSV-1, was developed for the amplification of HSV DNA in CSF. The method was found to be a rapid and non-invasive means of diagnosing HSE in a very early stage o f the disease; it was highly sensitive and specific. With a combinatio n of nested PCR assays for HSV-1 and HSV-2 (primers in the glycoprotei n G gene) in 10 mul of CSF, HSV DNA was detected in CSF from 88 out of 93 patients (95%) with HSE. Evidence of HSV-2 aetiology was found in 6 of 93 consecutive cases of HSE in immunocompetent patients by type-s pecific assays for the demonstration of HSV-2 DNA (primers in the gG g ene) and HSV-2 antibodies (to gG2 antigen) in the CSF. Five of the 6 p atients with HSV-2 encephalitis exhibited a clinical picture of severe HSE indistinguishable from that of ''classical'' HSV-1 encephalitis.T he combined use of PCR for the detection of HSV DNA in the CSF and the demonstration of intrathecal synthesis of antibodies to the virus wil l yield a reliable diagnosis and is now the method of choice for the d iagnosis of HSE. In order to elucidate pathogenetic mechanisms in HSE and to find out whether there are signs of a long-term persistence of an active infection in the CNS, pararameters of intrathecal immune act ivation were studied. Markers of the T-cellular immune response, such as neopterin and beta2M, were analysed in sequential samples collected during the acute phase and in long-term follow-up (1.1 - 15 years) in 20 patients with HSE and 30 with non-HSE. A vigorous intrathecal acut e inflammatory. response was found and also, in HSE but not in non-HSE , a long-term persistence (greater-than-or-equal-to 13 years) of the i ntrathecal immune activation. Various cytokines were subsequently stud ied in sequential samples of 9 patients with HSE. The findings clearly show that a compartmentalized non-specific as well as specific intrat hecal immune response occurs in HSE. The intrathecal response could be divided into 3 different phases: an acute stage (first week of illnes s) characterized by elevated CSF levels if, in particular, interleukin 6 (IL-6) and interferon gamma (IFN-gamma); an early convalescent stag e (2nd-6th week after onset of disease) associated with peaking levels of tumor necrosis factor alpha (TNF-alpha) and late markers of the ad aptive, T-cell mediated immune response like soluble intreleukin 2 rec eptor (sIL2-R) and soluble CD8 antigen (sCD8); and finally, a convales cent stage, lasting months - years and associated with persistently in creased levels of, in particular, sCD8. Three cytokines were either on ly demonstrable in occasional samples (IL-1) or not at all (TNF-beta a nd IL-4). The findings demonstrate the compartmentalization and provid e information on the kinetics of the inflammatory response in HSE. Alt hough CSF seems to be cleared of HSV DNA persistence of the intratheca l inflammatory process is demonstrated, which may have implications fo r anti-viral and anti-inflammatory therapy in HSE.