Introduction

Lactate secreted by tumors is not just a byproduct, but rather an active modulator of immune cells. There are few studies aimed at investigating the true effect of lactate, which is normally confounded by pH. Such a knowledge gap needs to be addressed. Herein, we studied the immunomodulatory effects of lactate on dendritic cells (DCs) and macrophages (MΦs).

Methods

Bone marrow-derived innate immune cells were treated with 50 mM sodium lactate (sLA) and incubated for 2 days or 5 days at 37 °C. Controls included media, lipopolysaccharide (LPS), MCT inhibitors (α-cyano-4-hydroxycinnamic acid and AR-C15585). Flow cytometric analysis of immune phenotypes were performed by incubating cells with specific marker antibodies and viability dye. Differential expression analyses were conducted on R using limma-voom and adjusted p-values were generated using the Bejamini-Hochberg Procedure.

Results

Lactate exposure attenuated DC maturation through the downregulation of CD80 and MHCII expression under LPS stimulation. For MΦs, lactate exposure resulted in M2 polarization as evidenced by the reduction of M1 markers (CD38 and iNOS), and the increase in expression of CD163 and Arg1. We also revealed the role of monocarboxylate transporters (MCTs) in mediating lactate effect in MΦs. MCT4 inhibition significantly boosted lactate M2 polarization, while blocking of MCT1/2 failed to reverse the immunosuppressive effect of lactate, correlating with the result of gene expression that lactate increased MCT4 expression, but downregulated the expression of MCT1/2.

Conclusions

This research provides valuable insight on the influence of metabolic products on tumor immunity and will help to identify novel metabolic targets for augmenting cancer immunotherapies.

中文翻译：

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乳酸暴露促进先天免疫细胞的免疫抑制表型

介绍

肿瘤分泌的乳酸不仅仅是一种副产品，而是一种免疫细胞的活性调节剂。很少有研究旨在调查乳酸的真实作用，这通常会被 pH 值混淆。这种知识差距需要解决。在此，我们研究了乳酸对树突状细胞 (DC) 和巨噬细胞 (MΦ) 的免疫调节作用。

方法

用 50 mM 乳酸钠 (sLA) 处理骨髓衍生的先天免疫细胞，并在 37 °C 下孵育 2 天或 5 天。对照包括培养基、脂多糖 (LPS)、MCT 抑制剂（α-氰基-4-羟基肉桂酸和 AR-C15585）。免疫表型的流式细胞术分析是通过将细胞与特异性标记抗体和活力染料一起孵育来进行的。使用 limma-voom 对 R 进行差异表达分析，并使用 Bejamini-Hochberg 程序生成调整后的 p 值。

结果

乳酸暴露通过在 LPS 刺激下下调 CD80 和 MHCII 表达来减弱 DC 成熟。对于 MΦ，乳酸暴露导致 M2 极化，这可以通过 M1 标志物（CD38 和 iNOS）的减少以及 CD163 和 Arg1 的表达增加来证明。我们还揭示了单羧酸转运蛋白 (MCT) 在介导 MΦ 中乳酸效应中的作用。MCT4抑制显着促进乳酸M2极化，而阻断MCT1/2未能逆转乳酸的免疫抑制作用，这与乳酸增加MCT4表达但下调MCT1/2表达的基因表达结果相关。

结论

这项研究为代谢产物对肿瘤免疫的影响提供了有价值的见解，并将有助于确定用于增强癌症免疫治疗的新代谢靶点。