Aging potentially reduces CD169 expression in sinus macrophages of pelvic lymph nodes.

The number of patients with prostate cancer has been increasing around the world. Although anticancer immunotherapy targeting the immune checkpoint molecules has been approved for many types of cancer, no significant anti-cancer effects have been observed in patients with prostate cancer. Lymph node sinus macrophages (LSMs) are known to work as antigen-presenting cells, which are critical for anticancer immune responses. Previous studies have suggested that CD169 expression in LSMs affects anticancer immune responses in several cancers, including prostate cancer. In the present study, we aimed to examine the correlation between the tumor immune microenvironment and activation status of LSMs in patients with prostate cancer. Forty-two cases of high-risk localized prostate cancer treated using robot-assisted laparoscopic radical prostatectomy and lymph node dissection between 2017 and 2021 were enrolled. CD169 expression in LSMs was examined by immunohistochemistry. The results indicated that CD169 expression in LSMs was significantly decreased in older (≥ 75 years) compared with younger patients. However, no significant correlation was found between CD169 expression and any other clinicopathological factors. In addition, CD3- and CD8-postitive lymphocytes in primary cancer tissues were evaluated in the same cases, and their correlations with CD169 expression in LSMs were tested. Although these lymphocytes tended to be higher in CD169^high than in CD169^low cases, the difference was not statistically significant. In conclusion, we found that CD169 expression was upregulated in older patients and tended to be related to T cell infiltration in cancer tissues. Therefore, the downregulation of CD169 in LSMs might be involved in the reduced anticancer immune response in prostate cancer.