The majority of trigeminal ganglia (TGs) are latently infected with alpha-herpesviruses [herpes simplex virus type-1 (HSV-1) and varicella-zoster virus (VZV)]. Whereas HSV-1 periodically reactivates in the TGs, VZV reactivates very rarely. The goal of this study was to determine whether herpesvirus latency is linked to a local immune cell infiltration in human TGs. T cells positive for the CD3 and CD8 markers, and CD68-positive macrophages were found in 30 of 42 examined TGs from 21 healthy individuals. The presence of immune cells correlated constantly with the occurrence of the HSV-1 latency-associated transcript (LAT) and only irregularly with the presence of latent VZV protein. In contrast, uninfected TGs showed no immune cell infiltration. Quantitative RT-PCR revealed that CD8, interferon-gamma, tumor necrosis factor-alpha, IP-10, and RANTES transcripts were significantly induced in TGs latently infected with HSV-1 but not in uninfected TGs. The persisting lymphocytic cell infiltration and the elevated CD8 and cytokine/chemokine expression in the TGs demonstrate for the first time that latent herpesviral infection in humans is accompanied by a chronic inflammatory process at an immunoprivileged site but without any neuronal destruction. The chronic immune response seems to maintain viral latency and influence viral reactivation.

The latent persistence of herpes simplex virus type 1 (HSV-1) in human trigeminal ganglia (TG) is accompanied by a chronic CD8 T-cell infiltrate. The focus of the current work was to look for HSV-1 transcription activity as a potential trigger of the immune response and to characterize the immune cell infiltrates by this feature. We combined in situ hybridization, laser cutting microscopy, and single cell RT-PCR to demonstrate the expression of the HSV-1 immediate early (IE) genes ICP0 and ICP4 in human trigeminal neurons. Using CDR3 spectratyping, we showed that the infiltrating T-cells are clonally expanded, indicating an antigen-driven immune response. Moreover, the persisting CD8+ T-cells had features of the memory effector phenotype. The voltage-gated potassium channel Kv1.3, a marker of chronic activated memory effector cells, and the chemokines CCL5 and CXCL10 were expressed by a subpopulation of infiltrating cells. The corresponding chemokine receptors CCR5 and CXCR3 were co-expressed on virtually all CD8 T-cells. In addition, T-cells expressed granzymes and perforin. In contrast to animal models of HSV-1 latency, hardly any FoxP3-positive regulatory T-cells were detected in human TG. Thus, HSV-1 IE genes are expressed in human TG and the infiltrating T-cells bear several characteristics that suggest viral antigenic stimulation.

The immune response to latent herpesvirus infections was compared in human trigeminal ganglia (TG) and dorsal root ganglia (DRG) of 15 dead individuals. On the basis of our previous findings, we hypothesized that T-cells would be attracted to sensory neurons latently infected with herpes simplex virus type 1 (HSV-1), but not to those harboring latent varicella zoster virus (VZV). We showed that the TG contain a positive hybridization signal for HSV-1 latency-associated transcript (LAT), whereas the DRG from the same individuals lack detectable LAT. In contrast, immunohistochemistry revealed that latent VZV protein 62 stained positive in the vast majority of all tested TG and DRG. T-cell infiltrates prominently surrounded individual neurons in the TG but not in the DRG. TaqMan polymerase chain reaction also showed higher expression of CD8 and RANTES transcripts in the TG versus DRG. Only the infiltrates in the TG, but not in the DRG, produced RANTES at the protein level. Because it has been shown that RANTES protein is produced only after T-cell receptor stimulation, we assume that T-cell infiltration is associated with antigen recognition in the TG but not in the DRG.

A gene expression study of mice treated with the tricyclic antidepressant amitriptyline was performed. To enable the detection of cell type-specific expression changes, lasermicrodissected nucleus accumbens was analysed after 4 and 28 days of treatment. After 4 days of treatment no significantly regulated genes could be detected in this study. In contrast, 95 genes exhibited different expression levels in animals treated for 28 days with amitrityline compared with sham animals. This observation reflects the long-term effects and adaptation processes observed in patients treated with this drug. Among the regulated genes are receptors belonging to the dopamine-dependent signalling cascade, ion channels (mainly voltage-dependent potassium and calcium channels) potentially involved in signalling cascades and neuropeptides. The results support the hypothesis that the therapeutic effect of this antidepressant is much more complex and not confined to a reuptake inhibition of neurotransmitters. Paradigms inducing only weak expression changes, which may be limited to certain cell types within the highly complex brain structure, can therefore be reliably investigated by applying a cell typespecific expression profiling technique based on laser microdissection and subsequent RNA amplification followed by DNA microarray analysis.

Human trigeminal ganglia were tested by double fluorescence in situ hybridization for the presence and distribution of herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV) latency. Latency transcripts of both viruses were detected in common areas within the ganglia. Also, a few single neurons were shown to harbor HSV-1 and VZV together.