DISCUSSION

In BD patients, the frequencies of CD45RO+ cells were lower than disease control group has been reported (Takase, et al., 2006) and also, in our laboratory we observed that the frequencies of CD8+CD44+ and CD8+CD62L- memory T cells in BD mice were significantly lower than BDN mice. Therefore, we investigated the expression of IL-15Rα and IL-7Rα which as known as association with generation of memory T cells (Kimberly, et al., 2003) in the HSV-induced BD mouse model. The expression of IL-15Rα was significantly lower in BD mice than BDN mice. Although serum level of IL-15 was not analyzed because mouse IL-15 ELISA kit was not available, IL-7 was not different between BD mice and BDN mice. Therefore, we focused in induction of IL-15Rα to up-regulate memory T cells in BD mice. There has been reported, the IL-15Rα mRNA induced during Poly I:C bystander responses in vivo (Lodolce, et al., 2001). It was also reported that administrated Poly I:C enhanced in type I IFN and TGFβ-mediated inflammation in systemic sclerosis (Rothstein, et al., 2010), airway inflammation in a rat model of asthma (Takayama, et al., 2011), and EAE (Experimental Autoimmune Uveitis) retinal autoimmunity model (Ren, et al., 2011). In contrast, many observations supports a protective role of Poly I:C supplementation in the diabetes prone BB rat (Sobel, et al., 1998), a murine Experimental autoimmune encephalomyelitis model (Touil, et al., 2006), and inflammatory arthritis model by IFN-α involvement (Yarilina, et al., 2007). In this experiment, we found low dose of Poly I:C effectively increased the level of IL-15Ra by dose dependent manner in vivo. Then, 0.2

µg/g of Poly I:C was injected intra-peritoneally into BD mice to induce IL-15Rα level. At 2 days after the last injection, we observed that cutaneous symptoms were particularly improved and the severity score of BD mice was decreased compared to PBS injected control group. In the same time, we observed the increased frequencies of IL-15Rα in PBMC and splenocytes significantly but there was no difference in the frequencies of IL-7Rα between Poly I:C and PBS injected BD mice group. Furthermore, the frequencies of CD8+CD44+ memory T cells were significantly increased in PBMC and splenocytes but the frequencies of CD4+CD44+ memory T cells were not different between Poly I:C and PBS injected BD mice group at 17 days after the last injection. In this result, CD8+CD44+

memory T cells were selectively up-regulated in BD mice by Poly I:C injection. Therefore, the increased CD8+CD44+ memory T cells could be correlated to IL-15Rα that was up-regulated by Poly I:C. Interestingly, although the frequency of IL-7Rα were not affected, the serum level of IL-7 significantly up-regulated by Poly I:C injection in BD mice. It is possible that the increased IL-7 cytokine also could be involved in up-regulation of CD8+CD44+ memory T cells. There are many papers associated with potent and selective stimulation of memory-phenotype CD8+ T cells in vivo by IL-15 (Zhang, et al., 1998;

Becker, et al., 2002; Becker, et al., 2003;Oh, et al., 2004; Mortier, et al., 2009) but are not required for memory-phenotype CD4+ T cells (Tan, et al., 2002). In addition, the expression of IL-15Rα in PBMC was steadily elevated by 17 days in contrast with return to PBS control level in splenocytes and lymph node cells. As has been reported that IL-15 and IL-15Rα, that form stable complexes on the cell surface of activated monocytes, recycled after endosomal

Sato, et al., 2007). It has been thought that highly IL-15Rα-expressing cells such as monocytes and macrophages were abundant in blood compared to spleen and lymph nodes.

The expression of IL-15Rα on cell surfaces enable sustained IL-15 activity by recycling. In our result, also has shown steady expression of IL-15Rα in PBMC. As a result, IL-15Rα induced CD8+ memory T cells were up-regulated at 17 days and the improvement of cutaneous symptoms of BD mice was also observed after Poly I:C injection. Then, what kind of factors affect improvement in HSV-induced BD mice model in early phase after poly I:C injection? Recent data has been revealed that Poly I:C stimulation of dendritic cells and fibroblasts limits herpes simplex virus type 1 infection in an IFN-β-dependent way (Gaajetaan, et al., 2011). And another data showed, Poly I:C suppress the effector phase of inflammatory arthritis and it is mediated by IFN-α involved in type I IFNs (Yarilina, et al., 2007). Also, Interferon-α2a (IFN-α2a) has been reported to be clinically effective in several patient groups with BD (Zouboulis, et al., 1998). When we evaluated the serum level of IFN-α in the PBS or Poly I:C injected BD mice using VeriKine^TM Mouse Interferon Alpha ELISA Kit from R&D Systems according to the manufacturer’s recommendations, the IFN-α levels in the mouse sera tested were below the detection limit of the kit (data not shown). We observed the mRNA level of IL-23R and serum level of IL-17A, as known as pro-inflammatory factor, were down-regulated in Poly I:C injected mice compared to control group at 2 days after the last injection. Also we found the frequencies of CD8+CD122+ T cells as known as newly identified regulatory T cells were significantly elevated in Poly I:C injected group compared with control group in lymph node cells at 17 days after the last Poly I:C injection. In addition, in our laboratory study, we observed that the frequencies of

IL-15Rα were down-regulated in peripheral blood mononuclear cells of BD patients compared with healthy control as a similar pattern with HSV-induced BD mouse model (data not shown). In conclusion, these results suggest that IL-15Rα is an important factor for the regulation of symptoms in HSV-induced BD mice.