Schematic of the proposed mechanism of lactate effects on T cells in the inflammatory site.

<p>(<b>A</b>) The motility of CD4⁺ and CD8⁺ T cells is blocked once they get exposed to elevated levels of lactate in the inflammatory site. Lactic acid also causes loss of cytolytic activity by CD8⁺ T cells, and sodium lactate promotes the production of IL-17 by CD4⁺ T cells. (<b>B</b>) Pharmacologic targeting of lactate transporters re-establish T cell migration away from the inflammatory site and block the production of high amounts of IL-17.</p

Inhibition of lactate transporters promotes the release of T-cells from the inflamed site in zymosan-induced peritonitis.

<p>(A) Lactate levels in the peritoneum of zymosan-treated mice. (B) Number of CD4⁺ and CD8⁺ T cells, respectively, in the peritoneal lavage of C57BL/6 mice injected i.p. with zymosan (1 mg/mouse) to induce peritonitis, and 5 d later, i.p. treated with phloretin (50 μM), an anti-Slc5a12 antibody (5 μg/ml) or an isotype control antibody. (C) Number of carboxyfluorescein succinimidyl ester (CFSE)-labeled activated CD4⁺ T cells in the peritoneal lavage (left panel) or spleen (right panel), respectively, of C57BL/6 mice injected i.p. with zymosan (1 mg/mouse), then i.p. treated with phloretin (50 μM), an anti-Slc5a12 specific antibody (5μg/ml) or an isotype control antibody. (A–C) <i>n</i> = 3 or more. Underlying numerical data and statistical analysis can be found in the supporting file, <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002202#pbio.1002202.s001" target="_blank">S1 Data</a>, Fig 6A–6C. Values denote mean ± SD. <i>*p <</i> 0.05; <i>**p <</i> 0.01; <i>***p <</i> 0.001.</p

Sodium lactate and lactic acid act on CD4⁺ and CD8⁺ T cell subsets, respectively, through specific cell membrane transporters.

<p>(A) Total protein levels of the transporters Slc16a1 and Slc5a12 as assessed by western blot in activated CD4⁺ and CD8⁺ T cell subsets. (B–D) In vitro chemotaxis (4 h time point) of activated CD8⁺ T cells towards CXCL10 (300 ng/ml) in the presence of lactic acid (10 mM) alone, or in combination with α-cyano-4-hydroxycinnamate (CHC) (425 μM), phloretin (25 μM), or anti-Slc16a1 antibody (2.5 μg/ml) (B), or increasing concentrations of AR-C155858 as indicated in the figure (C), and activated CD4⁺ T cells towards CXCL10 (300 ng/ml) in the presence of sodium lactate (10 mM) alone, or in combination with an anti-Slc5a12 antibody (2.5 μg/ml) or two specific short hairpin RNAs (shRNAs) (D). An isotype control antibody has been included to control for antibody specificity (B, D), and a nonspecific shRNA has been included to control for gene knockdown specificity (D). (B–D) <i>n</i> = 3. Underlying numerical data and statistical analysis can be found in the supporting file, <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002202#pbio.1002202.s001" target="_blank">S1 Data</a>, Fig 2B–2D. Values denote mean ± SD. <i>*p <</i> 0.05; <i>**p <</i> 0.01; <i>***p <</i> 0.001.</p

Lactate modulates effector T cell functions.

<p>(A) Relative mRNA expression levels of the cytokines interferon-gamma (<i>Ifn-γ</i>), <i>Tnf-β</i>, <i>Il-4</i>, <i>Il-5</i>, <i>Il-13</i>, and <i>Il-17</i> and of the transcription factor <i>Rorc</i> as assessed by qRT-PCR in CD4⁺ subsets Th0, Th1, Th2, and Th17 treated with sodium lactate (10 mM) or left untreated. mRNA levels of each cytokine expressed by untreated Th0 cells were set to 1. (B) Intracellular staining of IL-17A and IFN-γ in activated CD4⁺ T cells treated with sodium lactate (10 mM) or left untreated. (C) Relative mRNA expression levels of <i>Il-17</i> and <i>Rorc</i> in activated CD4⁺ T cells treated with sodium lactate alone or in combination with an anti-Slc5a12 antibody. mRNA levels of untreated T cells were set to 1. (D) Cell survival of allogeneic endothelial cells in the presence of CD8⁺ cytotoxic T cells and lactic acid (10 mM) or sodium lactate (10 mM) shown as kinetic (left panel) and 6 h time point (right panel). (A, C, D left panel) Data is representative of three independent experiments; the underlying numerical data and statistical analysis for each independent experiment can be found in the supporting file, <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002202#pbio.1002202.s001" target="_blank">S1 Data</a>, Fig 4A, 4C, and 4D. (B, D right panel) <i>n</i> = 3. (A–D) Underlying numerical data and statistical analysis can be found in the supporting file, <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002202#pbio.1002202.s001" target="_blank">S1 Data</a>, Fig 4A–4D. Values denote mean ± SD. <i>*p <</i> 0.05; <i>**p <</i> 0.01.</p