Department of Hygiene, Kawasaki Medical School, Kurashiki, 701-0192, Japan.
Department of Life Sciences, Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, 727-0023, Shobara, Japan.
Environ Health Prev Med. 2021 Apr 19;26(1):50. doi: 10.1186/s12199-021-00967-9.
Asbestos fibers possess tumorigenicity and are thought to cause mesothelioma. We have previously reported that exposure to asbestos fibers causes a reduction in antitumor immunity. Asbestos exposure in the mixed lymphocyte reaction (MLR) showed suppressed induction of cytotoxic T lymphocytes (CTLs), accompanied by a decrease in proliferation of CD8 T cells. Recently, we reported that asbestos-induced suppression of CTL induction is not due to insufficient levels of interleukin-2 (IL-2). In this study, we continue to investigate the mechanism responsible for the effect of asbestos fibers on the differentiation of CTLs and focus on interleukin-15 (IL-15) which is known to be a regulator of T lymphocyte proliferation.
For MLR, human peripheral blood mononuclear cells (PBMCs) were cultured with irradiated allogenic PBMCs upon exposure to chrysotile B asbestos at 5 μg/ml for 7 days. After 2 days of culture, IL-15 was added at 1 ng/ml. After 7 days of MLR, PBMCs were collected and analyzed for phenotypic and functional markers of CD8 T cells with fluorescence-labeled anti-CD3, anti-CD8, anti-CD45RA, anti-CD45RO, anti-CD25, and anti-granzyme B antibodies using flow cytometry. To examine the effect of IL-15 on the expression level of intracellular granzyme B in proliferating and non-proliferating CD8 lymphocytes, PBMCs were stained using carboxyfluorescein diacetate succinimidyl ester (CFSE) and then washed and used for the MLR.
IL-15 addition partially reversed the decrease in CD3CD8 cell numbers and facilitated complete recovery of granzyme B cell percentages. IL-15 completely reversed the asbestos-induced decrease in percentage of granzyme B cells in both non-proliferating CFSE-positive and proliferating CFSE-negative CD8 cells. The asbestos-induced decrease in the percentage of CD25 and CD45RO cells in CD8 lymphocytes was not reversed by IL-15.
These findings indicate that CTLs induced upon exposure to asbestos possess dysfunctional machinery that can be partly compensated by IL-15 supplementation, and that IL-15 is more effective in the recovery of proliferation and granzyme B levels from asbestos-induced suppression of CTL induction compared with IL-2.
石棉纤维具有致癌性，被认为会导致间皮瘤。我们之前曾报道过，接触石棉纤维会导致抗肿瘤免疫能力下降。在混合淋巴细胞反应（MLR）中，石棉暴露会抑制细胞毒性 T 淋巴细胞（CTL）的诱导，同时 CD8 T 细胞的增殖减少。最近，我们报道称，石棉诱导的 CTL 诱导抑制不是由于白细胞介素-2（IL-2）水平不足所致。在这项研究中，我们继续研究石棉纤维对 CTL 分化的影响机制，并重点研究白细胞介素-15（IL-15），因为它是 T 淋巴细胞增殖的调节剂。
对于 MLR，将人外周血单核细胞（PBMCs）与照射后的同种异体 PBMCs 一起在 5μg/ml 的温石棉 B 下培养 7 天。培养 2 天后，加入 1ng/ml 的 IL-15。MLR 7 天后，收集 PBMCs，并用荧光标记的抗 CD3、抗 CD8、抗 CD45RA、抗 CD45RO、抗 CD25 和抗颗粒酶 B 抗体通过流式细胞术分析 CD8 T 细胞的表型和功能标记。为了研究 IL-15 对增殖和非增殖 CD8 淋巴细胞中细胞内颗粒酶 B 表达水平的影响，用羧基荧光素二乙酸琥珀酰亚胺酯（CFSE）对 PBMCs 进行染色，然后洗涤并用于 MLR。
IL-15 的添加部分逆转了 CD3CD8 细胞数量的减少，并促进了颗粒酶 B 细胞百分比的完全恢复。IL-15 完全逆转了石棉诱导的非增殖 CFSE 阳性和增殖 CFSE 阴性 CD8 细胞中颗粒酶 B 细胞百分比的降低。IL-15 并未逆转石棉诱导的 CD8 淋巴细胞中 CD25 和 CD45RO 细胞百分比的降低。
这些发现表明，暴露于石棉后诱导的 CTL 具有功能失调的机制，可通过 IL-15 补充部分补偿，并且与 IL-2 相比，IL-15 更有效地恢复增殖和颗粒酶 B 水平，从而抑制 CTL 的诱导。
