Summary auto-generated
This 1983 study examined how the blood-brain barrier (BBB) affects antibody-mediated clearance of herpes simplex virus type 1 (HSV-1) from the central nervous system. Using a mouse model where HSV-1 was inoculated into the footpad, researchers tracked virus spread to the spinal cord and monitored BBB integrity using radiolabeled IgG tracers. Virus reached the spinal cord within 48 hours and replicated to high titers by day 4, yet clinical paralysis did not appear until day 6. Critically, BBB disruption—detected by IgG tracer leakage—occurred only on day 6, after virus had already established infection. In contrast, neutralizing antibodies rapidly cleared virus from the footpad within 72 hours but failed to clear virus from intracerebrally inoculated brain tissue. These findings suggest the BBB prevents effective IgG access during early CNS infection, allowing virus replication to proceed unchecked in neural tissue despite circulating antibodies. The results help explain why HSV-1 encephalitis can occur in seropositive individuals and have implications for understanding herpes virus pathogenesis and developing immunotherapies.
Key findings
- HSV-1 virus reaches the spinal cord by 48 hours but the blood-brain barrier remains intact until day 6, after clinical symptoms appear
- Neutralizing IgG rapidly clears virus from peripheral sites (footpad) within 72 hours but fails to clear intracerebrally inoculated brain virus, indicating BBB-restricted antibody access to CNS tissue
- Early inflammatory infiltrates (myelitis) appear in the spinal cord by day 3, but significant BBB disruption is delayed until day 6, demonstrating late breakdown of barrier integrity relative to early infection stages
- The BBB's relative integrity during early infection permits prolonged unrestricted viral replication in CNS tissue compared to peripheral tissues, potentially explaining HSV-1 encephalitis in previously seropositive patients
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Abstract
Following footpad inoculation in mice, herpes simplex virus type 1 spreads along nerves to the spinal cord where a myelitis causes hind limb paralysis beginning on day 6. Neutralizing antibody effectively prevents this illness only if given within 72 h. We therefore studied the timing of blood-brain barrier (BBB) disruption relative to the appearance of virus and inflammatory cell infiltrates in the spinal cord. Virus was detectable in dorsal root ganglion and spinal cord explants by 48 h. By 72 h, mononuclear cell infiltrates were evident in the spinal cord. By day 4, high titres of virus were demonstrable in the spinal cord. On day 6 125I-labelled IgG tracers penetrated the spinal cord BBB. In addition, using a passive transfer model, mice given neutralizing IgG completely cleared footpad virus within 72 h while brain virus titres were unaffected by IgG treatment up to day 7. These observations indicate that the BBB may prevent IgG-mediated virus clearance during the early stages of infection.