Summary Immune cells regulate a hypertonic microenvironment in the skin; however, the biological advantage of increased skin Na+ concentrations is unknown. We found that Na+ accumulated at the site of bacterial skin infections in humans and in mice. We used the protozoan parasite Leishmania major as a model of skin-prone macrophage infection to test the hypothesis that skin-Na+ storage facilitates antimicrobial host defense. Activation of macrophages in the presence of high NaCl concentrations modified epigenetic markers and enhanced p38 mitogen-activated protein kinase (p38/MAPK)-dependent nuclear factor of activated T cells 5 (NFAT5) activation. This high-salt response resulted in elevated type-2 nitric oxide synthase (Nos2)-dependent NO production and improved Leishmania major control. Finally, we found that increasing Na+ content in the skin by a high-salt diet boosted activation of macrophages in an Nfat5-dependent manner and promoted cutaneous antimicrobial defense. We suggest that the hypertonic microenvironment could serve as a barrier to infection.

Inflammation and infection can trigger local tissue Na + accumulation. This Na +-rich environment boosts proinflammatory activation of monocyte/macrophage-like cells (MΦs) and their antimicrobial activity. Enhanced Na +-driven MΦ function requires the osmoprotective transcription factor nuclear factor of activated T cells 5 (NFAT5), which augments nitric oxide (NO) production and contributes to increased autophagy. However, the mechanism of Na + sensing in MΦs remained unclear. High extracellular Na + levels (high salt [HS]) trigger a substantial Na + influx and Ca 2+ loss. Here, we show that the Na + /Ca 2+ exchanger 1 (NCX1, also known as solute carrier family 8 member A1 [SLC8A1]) plays a critical role in HS-triggered Na + influx, concomitant Ca 2+ efflux, and subsequent augmented NFAT5 accumulation. Moreover, interfering with NCX1 activity impairs HS-boosted inflammatory signaling, infection-triggered autolysosome formation, and subsequent antibacterial activity. Taken together, this demonstrates that NCX1 is able to sense Na + and is required for amplifying inflammatory and antimicrobial MΦ responses upon HS exposure. Manipulating NCX1 offers a new strategy to regulate MΦ function.

Prostaglandin (PG) D2 has been shown to be transformed by human 11-ketoreductase to 9a,11f-PGF2, a biologically active metabolite that is produced in vivo. During the course of developing a mass spectrometric assay for 9a,113-PGF2, several compounds with characteristics similar to PGF2 were detected in both plasma and urine of normal humans by selected ion monitoring. Analysis of pooled plasma obtained from patients with mastocytosis during severe episodes of systemic mast cell activation associated with the release of markedly increased quantities of PGD2 was revealing in that all of these compounds were present in approximately 800-fold greater abundance compared to levels found in normal plasma, suggesting that these compounds arose from PGD2 metabolism.Complete electron impact mass spectra were obtained of these compounds in both plasma and urine; these spectra established that they were all isometric forms of PGF2. Approximately 16 isomeric PGF2 compounds were identified. Treatment with butylboronic acid indicated that the C-9 and C-11 hydroxyls were trans in approximately one-third ofthe compounds and cis in approximately two-thirds. Preliminary experiments suggest that PGD2 is a very labile compound in vivo and undergoes extensive isomerization, after which reduction by 11-ketoreductase yields a family of more stable isomeric PGF2 compounds. Elucidating the profile of biological activity of these compounds and their mechanism of formation will contribute importantly to our understanding of the biological consequences of PGD2 release in vivo. These results also bring into question the reliability of assays for PGFu and its metabolites in human biological fluids as a specific index of endogenous PGFu biosynthesis, as these assays may also measure in part isomeric PGF2 compounds arising from PGD2 metabolism.Prostaglandin (PG) D2 is the principal cyclooxygenase product produced by mast cells (1, 2). PGD2 is released in markedly increased quantities in patients during episodes of systemic mast cell activation and is a major mediator of the humoral manifestations of such episodes (3, 4). PGD2 has also been considered as a potential mediator in the human pulmonary allergic response (5) and recently has been shown to be released into the lower respiratory tract during acute antigen challenge in patients with allergic asthma (6). PGD2 is metabolized in vivo predominantly via a 11-ketoreductase pathway to PGF-ring metabolites (7)(8)(9). In vitro studies demonstrated that human liver 11-ketoreductase stereospecifically transforms PGD2 to 9a,11/3-PGF2 (10), a finding that subsequently has been generalized to 11-ketoreductase metabolism of PGD2 in other human and animal tissues and organs (11)(12)(13)(14). Importantly, 9a,11,8-PGF2 has been shown to be produced in vivo and to be a biologically active metabolite that is a pressor substance in the rat (10), inhibits platelet aggregation (11, 15), and causes both human coronary and human bronchial smooth muscle to contract (13,14).Because of the potential importa...

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