Cytokine and chemokine production in HSV-1 latently infected trigeminal ganglion cell cultures: Effects of hyperthermic stress

Abstract The establishment of a primary trigeminal ganglion (TG) cell culture latently infected with herpes simplex virus type 1 (HSV-1) has been useful in studying stress-induced reactivation of the latent virus. However, the immune profile of this culture system prior to and after stress has never been established. In the present manuscript, cytokine and chemokine production were measured in primary cultures of TG cells obtained from uninfected and HSV-1 latently infected mice. Supernates from TG cell cultures contained detectable interleukin (IL)-6 but not IL-1 β , IL-2, IL-10, interferon (IFN)- γ or tumor necrosis factor (TNF)- α as determined by ELISA. The basal level of IL-6 in uninfected TG cell cultures was 20.5±2.3 ng/ml, whereas latently infected TG cells produced significantly less IL-6 (12.1±1.9 ng/ml). Supernates from TG cell cultures also contained detectable levels of C-10, MCP-1 and eotaxin but little to no MIP-1 α , MIP-1 β , or MIP-2. While there were no differences in the basal level of MCP-1 and eotaxin in TG cell cultures from HSV-1-infected and uninfected mice, C10 levels were significantly higher in TG cultures originating from infected mice compared to uninfected ones (5.86±0.61 ng/ml compared to 1.18±0.16 ng/ml). Hyperthermic stress (43°C, 180 min), which induces reactivation of latent HSV-1 from TG cell cultures, significantly reduced IL-6 and C-10 levels from both uninfected and latently infected TG cell cultures. However, there was no correlation between cytokine/chemokine levels and HSV-1 reactivation. Immunofluorescent studies showed TG cell cultures contained 10% MAC-3 + staining cells (macrophage specific) but no dendritic cells. By comparison, cells from freshly isolated TG contained 6% positive dendritic cells but + cells. Both in vivo and in vitro TG consisted of a low percentage of CD3 + and CD8 + cells. Hyperthermic stress (43°C for 3 h) eliminated the lymphocyte population as determined by RT-PCR. Whereas no spontaneous reactivation has been reported in mice, spontaneous reactivation occurred in 4.5% (10/220) of TG cell cultures surveyed over a 20 day period. Collectively, the dichotomy between HSV-1 replication and reactivation comparing the in vitro and in vivo HSV-1 latency models may reside, in part, to the differences in the levels of cytokines, chemokines and immune cell populations within the microenvironment of the in vitro and in vivo TG.