Anti-herpes simplex type 1 activity in IgG subclasses produced systemically and intrathecally in patients with herpes encephalitis

Spread of herpes simplex virus type 1 in the central nervous system during experimentally reactivated encephalitis

Because many of the features of reactivated herpes simplex virus type 1 (HSV-1) central nervous systems (CNS) infections in vivo are incompletely understood, we used an animal model to study the development of the morphological, ultrastructural, radiological and immunological changes which occurred during acute and experimentally reactivated diseases. Rabbits were intranasally inoculated with HSV-1, and their latent trigeminal ganglionic and CNS infections were reactivated by intravenous injection of cyclophosphamide and dexamethasone. Technetium brain scans were performed to localize areas of blood-brain barrier breakdown, and cerebrospinal fluid (CSF) was analysed for IgG content by radial immunodiffusion assays. Nervous system tissues were studied by in situ hybridization and by immunofluorescent, light and electron microscopic techniques. Diffuse uptake of technetium was observed as HSV-1 spread transsynaptically into the brain during the acute phase of infection, and viral antigens and nucleic acids were detected in both the CNS olfactory and trigeminal systems. During latency, viral RNA was detected in the nuclei of neurons within the CNS olfactory cerebral and entorhinal cortices, indicating that HSV-1 became latent within the same CNS structures that were involved during the acute phase of infection. Following drug-induced reactivation, the brain scans revealed a more focal breakdown of the blood-brain barrier, and both neurons and neuronal processes in the entorhinal and olfactory cortices contained viral nucleic acids which correlated with the ultrastructural presence of HSV-1 virions. During the reactivated phase of infection a marked increase in the CSF IgG index occurred without an increase in the CSF: serum albumen ratio indicating a prompt intrathecal response in infected rabbits as compared to controls. To some extent, the CSF IgG index reflected the degree of histopathological damage.

Differential IgG subclass responses to epitopes in transmembrane protein of HIV-1

The human IgG subclass response to epitopes of gp41, the transmembrane protein of HIV-1, was characterized. Twenty sera that reacted with a synthetic peptide, residues 583-599 of the env product, were analyzed in subclass-specific enzyme immunoassays with this and three other peptides: the inverted sequence (599-583; HIV-env:inv), an overlapping sequence (586-606), and one derived from the 3' end of the env gene (848-863). Also, the IgG subclass reactivities with the 583-599, 586-606 and 604-625 sequences of sera from 38 patients in various stages of HIV infection were studied. IgG1 was the most prevalent subclass. Most of the few IgG2-IgG4 reactions occurred with the peptide of the strongest antigenicity, HIV-env 604-625. The sera with detectable IgG2-IgG4 reactivity were titered to allow subclass comparisons in regions below absorbance plateaus. Two sera showed proportionately higher IgG3 relative to total IgG reactivity with HIV-env 583-599 than with HIV-env 586-606, which is indirect evidence that distinct antibody populations in these sera recognize these overlapping peptide sequences. Individual differences in the antibody response to this region may affect the immunologic control of the virus. Isotype analyses can contribute to dissection of these individualities, as shown here. High IgG reactivity with HIV-env 583-599, which was linked to absence of symptoms, resided largely in the IgG1 subclass. We found no other unambiguous association between clinical status and any IgG subclass pattern.

Specific IgG subclass reactivity in herpes simplex encephalitis

Serum and cerebrospinal fluid (CSF) samples from 19 patients with a previous diagnosis of herpes simplex virus encephalitis (HSVE), from 14 patients with a previous diagnosis of non HSVE encephalitis and from 21 healthy subjects were examined to detect IgG subclasses 1-4 reactive with herpes simplex virus (HSV), cytomegalovirus (CMV) and varicella zoster virus (VZV). Antibodies to HSV were detected in CSF and serum from the 14 HSVE-patients with a reactivated HSV infection and from 3 of the 5 patients with a primary HSV infection. The predominant subclass pattern was an early HSV-specific IgG1 rise, followed by IgG3 and, more seldom, IgG4; HSV IgG2 was rarely seen. In HSVE patients, HSV IgG3 was absent in early samples and usually appeared 10-20 days after onset of disease. In 14 out of 16 seropositive healthy controls, on the other hand, HSV IgG3 was present in the CSF. Rising VZV IgG levels in serum and CSF were found in 11 HSVE patients. Eight of them showed signs of intrathecal VZV IgG1 synthesis. The VZV IgG reactivity was restricted to IgG1 in 7 of these whereas the HSV IgG subclass response also included IgG3 or 4. The appearance of several HSV IgG subclasses appeared to serve as a marker of HSV infection in spite of the serological VZV reaction, usually restricted to VZV IgG1. Intrathecal synthesis of the quantitatively minor HSV IgG3 and 4 subclasses was detected earlier than intrathecal synthesis of total HSV IgG, dominated by IgG1 in 4 patients with HSVE.

Herpes simplex virus encephalitis in children

Herpes simplex encephalitis (HSE) is an uncommon disease, yet 25 to 30 per cent of cases involve children. The initial clinical findings are nonspecific (fever, altered mental status), but most cases evolve to demonstrate focal neurologic signs and symptoms. The CSF is abnormal in over 90 per cent of cases. The EEG, CT, and MRI will further help in detecting focal encephalitis. The clinician caring for a child with focal encephalitis should institute broad-spectrum antimicrobial therapy plus acyclovir, pending definitive diagnosis by ancillary tests or brain biopsy, which is positive for HSE 33 to 55 per cent of the time and is diagnostic for other treatable conditions 10 to 20 per cent of the time. Acyclovir is the drug of choice for HSE and substantially reduces mortality and morbidity. The management of HSE in a child requires an experienced team of specialists and laboratory support in a tertiary intensive care setting.