Search

CD8 + T cells can switch between fatty acid catabolism and mitochondrial energy metabolism to sustain expansion and their cytotoxic functions. ST-4 is a TCR-enhanced mutant derived from superantigen staphylococcal enterotoxin C2 (SEC2), which can hyperactivate CD4 + T cells without MHC class II molecules. However, whether ST-4/SEC2 can enhance metabolic reprogramming in CD8 + T cells remains poorly understood. In this study, we found that ST-4, but not SEC2, could induce proliferation of purified CD8 + T cell from BALB/c mice in Vβ8.2- and -8.3-specific manners. Results of gas chromatography-mass spectroscopy analysis showed that fatty acid contents in CD8 + T cells were increased after ST-4 stimulation. Flow cytometry and Seahorse analyses showed that ST-4 significantly promoted mitochondrial energy metabolism in CD8 + T cells. We also observed significantly upregulated levels of gene transcripts for fatty acid uptake and synthesis, and significantly increased protein expression levels of fatty acid and mitochondrial metabolic markers of mTOR/PPARγ/SREBP1 and p38-MAPK signaling pathways in ST-4-activated CD8 + T cells. However, blocking mTOR, PPARγ, SREBP1, or p38-MAPK signals with specific inhibitors could significantly relieve the enhanced fatty acid catabolism and mitochondrial capacity induced by ST-4. In addition, blocking these signals inhibited ST-4-stimulated CD8 + T cell proliferation and effector functions. Taken together, our findings demonstrate that ST-4 enhanced fatty acid and mitochondria metabolic reprogramming through mTOR/PPARγ/SREBP and p38-MAPK signaling pathways, which may be important regulatory mechanisms of CD8 + T cell activation. Understanding the effects of ST-4-induced regulatory metabolic networks on CD8 + T cells provide important mechanistic insights to superantigen-based tumor therapy., (Copyright © 2020 by The American Association of Immunologists, Inc.)

Fatty acids (FAs) are essential constituents of cell membranes, signaling molecules, and bioenergetic substrates. Because CD8(+) T cells undergo both functional and metabolic changes during activation and differentiation, dynamic changes in FA metabolism also occur. However, the contributions of de novo lipogenesis to acquisition and maintenance of CD8(+) T cell function are unclear. In this article, we demonstrate the role of FA synthesis in CD8(+) T cell immunity. T cell-specific deletion of acetyl coenzyme A carboxylase 1 (ACC1), an enzyme that catalyzes conversion of acetyl coenzyme A to malonyl coenzyme A, a carbon donor for long-chain FA synthesis, resulted in impaired peripheral persistence and homeostatic proliferation of CD8(+) T cells in naive mice. Loss of ACC1 did not compromise effector CD8(+) T cell differentiation upon listeria infection but did result in a severe defect in Ag-specific CD8(+) T cell accumulation because of increased death of proliferating cells. Furthermore, in vitro mitogenic stimulation demonstrated that defective blasting and survival of ACC1-deficient CD8(+) T cells could be rescued by provision of exogenous FA. These results suggest an essential role for ACC1-mediated de novo lipogenesis as a regulator of CD8(+) T cell expansion, and may provide insights for therapeutic targets for interventions in autoimmune diseases, cancer, and chronic infections.

Dendritic cells (DC) are professional APCs that regulate innate and adaptive immunity. The role of fatty-acid synthesis in DC development and function is uncertain. We found that blockade of fatty-acid synthesis markedly decreases dendropoiesis in the liver and in primary and secondary lymphoid organs in mice. Human DC development from PBMC precursors was also diminished by blockade of fatty-acid synthesis. This was associated with higher rates of apoptosis in precursor cells and increased expression of cleaved caspase-3 and BCL-xL and downregulation of cyclin B1. Further, blockade of fatty-acid synthesis decreased DC expression of MHC class II, ICAM-1, B7-1, and B7-2 but increased their production of selected proinflammatory cytokines including IL-12 and MCP-1. Accordingly, inhibition of fatty-acid synthesis enhanced DC capacity to activate allogeneic as well as Ag-restricted CD4(+) and CD8(+) T cells and induce CTL responses. Further, blockade of fatty-acid synthesis increased DC expression of Notch ligands and enhanced their ability to activate NK cell immune phenotype and IFN-γ production. Because endoplasmic reticulum (ER) stress can augment the immunogenic function of APC, we postulated that this may account for the higher DC immunogenicity. We found that inhibition of fatty-acid synthesis resulted in elevated expression of numerous markers of ER stress in humans and mice and was associated with increased MAPK and Akt signaling. Further, lowering ER stress by 4-phenylbutyrate mitigated the enhanced immune stimulation associated with fatty-acid synthesis blockade. Our findings elucidate the role of fatty-acid synthesis in DC development and function and have implications to the design of DC vaccines for immunotherapy.

We have examined the effect of composition on the immunogenicity in mice of liposomal model membranes sensitized with dinitrophenyl-epsilon-aminocaproyl-phosphatidylethanolamine (DNP-Cap-PE) derivatives. Neither cholesterol content nor incorporation of exogenous charged amphiphile (dicetylphosphate, stearylamine) exerted a significant influence on the in vivo anti-DNP response as measured by the appearance of direct plaque-forming cells in the spleen. Similarly, the nature of the fatty acids (saturated vs unsaturated) present in DNP-Cap-PE had no effect. In contrast, the nonpolar region of the basic phospholipids comprising the liposomal bilayers played an important role as revealed by a comparative study of model membranes prepared with beef sphingomyelin (SM), egg phosphatidylcholine (PC), and synthetic distearoyl-, dimyristoyl-, dilauroyl-, and dioleoyl-phosphatidylcholines (DSPC, DMPC, DLPC, DOPC). Thus, liposomes with a large content of phospholipids possessing a high transition temperature (e.g., beef SM, DSPC) were more immunogenic than those containing phospholipids of low transition temperature (e.g., egg PC, DOPC). This correlation held for both unsonicated and sonicated liposomes. These findings may have a bearing on the phenomenon of membrane-localized antigen expression.

Hen egg albumin (HEA), heavily conjugated with dodecanoic acid (D-HEA), stimulated sustained delayed type hypersensitivity (DTH) specific for HEA without detectable antibody formation in guinea pigs. An oil-in-water emulsion containing purified BCG cell walls attached to the oil drops was found to be a very effective adjuvant for enhancing DTH to D-HEA, but not to HEA. Animals immunized with D-HEA in the BCG cell wall emulsion produced skin test reactions 2.4 cm in diameter when challenged with HEA 21 days after a single immunization. Control animals immunized with D-HEA in saline produced skin reactions 1 cm in diameter to similar challenge. Neither group of animals produced detectable antibody to HEA-OR D-HEAmThe emulsion had no adjuvant effect if the BCG cell walls were suspended in the aqueous phase and not attached to the oil droplets. Dodecanoic acid conjugated Salmonella typhi organisms could be used in place of the BCG cell walls to produce effective adjuvant preparations. Fruend's complete adjuvant and other water-in-oil emulsions, however, were found to be ineffective adjuvants for enhancing the degree of DTH produced by D-HEA. Experiments with autoradiography demonstrated that effective adjuvant preparations promote the localization and retention of both 125-I-labeled D-HEA and 125-I-labeled BCG cell walls in the paracortical area of lymph nodes where they are in close proximity to many T-type lymphocytes which proliferate in the induction of DTH.

If bovine serum albumin (BSA) is covalently conjugated with dodecanoic acid, its ability to stimulate delayed-type hypersensitivity (DTH) is enhanced whereas its ability to stimulate antibody production is suppressed. Conjugates of BSA prepared with negatively charged succinyl groups and positively charged amidine groups were unable to stimulate any detectable DTH to BSA even though their ability to bind anti-BSA antibody in a radioimmunoassay was similar to that of dodecanoyl-BSA which stimulated strong, sustained DTH. By analyzing a series of conjugates of BSA with fatty acids of varying chain length, we found that enhancement of the ability of a preparation to stimulate DTH to BSA could be separated from the suppression of its ability to stimulate antibody formation. The ability of a preparation to stimulate DTH correlated with the covalent conjugation of a large number of hydrophobic groups whereas the suppression of the ability to stimulate antibody formation correlated with covering of antibody-combining sites as measured in a radioimmunoassay.