| Summary: | 碩士 === 國立臺灣大學 === 獸醫學研究所 === 95 === Natural killer cell ( NKC) play an important role in innate immune responses. They kill virus infected cells and tumor cells without previous sensitization that lack or have a modified major histocompatibility class I surface molecule. The function of NK cells is regulated by a balance of activating receptors and inhibitory receptors. NK cells have been well-studied in many species, including humans, mouse, rat, procine and bovine. As for canine species, there is lack of data related to NK cell specific receptors or markers. Previous study of our laboratory had discovered that CD5 positive cells in canine peripheral blood lymphocytes can be divided into two populations, CD5 low density (CD5lo) cells and CD5 high density (CD5hi) cells. The size of CD5lo cells were larger than most of T cells and CD5hi cells, and contained numerous large cytoplasmic granules after IL-2 stimulation examined by light and electron microscopy. For this reason, we further studied and prove that after IL-2 stimulation, the CD5lo cell had strong cytotoxicity for CTAC, the target cell for canine NKC, after IL-2 stimulation. In addition, by Real-time RT-PCR, we found that CD5lo PBL had higher level of mRNAs of NK cell-related receptor than CD5hi PBL including NKG2D, CD16, CD94, CD160, perforin and Granzyme B. After IL-2 stimulation, CD5lo cells had significantly higher NK cell-related receptor mRNAs than CD5hi cells including NKp30, NKp44 , CD16 and CD94. Taken together, we belive that CD5lo subset is strongly associated with canine NKC activities. This is the first report to detaily characterize CD5lo in canine speies. These findings are useful for the study of canine NKC.
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