Systemic and phagosomal heat as overlooked regulators of neutrophil immunity

The National Institute of Allergy and Infectious Diseases awarded the University of Tennessee $235,550 on July 21, 2026, under the Allergy and Infectious Diseases Research program (CFDA 93.855, Assistance Listing Project Grant R21AI196150).

The award funds research into systemic and phagosomal heat as regulators of neutrophil immunity during bacterial infection. The project investigates how febrile temperatures reprogram neutrophil metabolism and function to enhance antibacterial defense against Staphylococcus aureus, and how localized heat within the neutrophil phagosome potentiates reactive oxygen species and acid stress to kill bacteria. Aim 1 examines how fever accelerates granulopoiesis and remodels bone marrow progenitors and neutrophil effector functions in vivo using temperature-controlled infection models. Aim 2 develops a fluorescent-thermometer S. aureus reporter strain to directly measure phagosomal temperature and test how heat, reactive oxygen species, and acid stress intersect to determine bacterial survival or death. The research addresses sepsis outcomes and aims to reveal temperature-sensitive therapeutic targets.

Performance occurs in Knoxville, Tennessee. The period of performance runs from the award date through June 30, 2028.

Abstract

Heat is a fundamental but overlooked variable in host-pathogen interactions. During infection, systemic heat manifests as fever (38-41°c), while local subcellular "hot spots" arise where oxidative metabolism and the neutrophil oxidative burst elevate temperatures above 50°c. Yet nearly all studies are performed at 37°c and in mice housed at standard temperatures that suppress physiologic fever, obscuring how heat shapes immunity and microbial survival. Our preliminary data reveal that febrile temperatures reprogram neutrophil metabolism toward oxidative killing and that the neutrophil phagosome itself acts as a thermal microenvironment that amplifies bacterial stress during the oxidative burst. . The objective of this proposal is to define how systemic fever and localized phagosomal heat reprogram neutrophil function, staphylococcus aureus physiology, and antibacterial activity. To address this, we will pursue two integrated aims. In aim 1, we hypothesize that febrile temperature accelerates granulopoiesis and reprograms neutrophil function in vivo to enhance antibacterial defense. Using temperature-controlled infection models, we will define how febrile conditions remodel bone marrow progenitors, neutrophil effector functions, and metabolic pathways that support host defense. In aim 2, we hypothesize that phagosomal heat potentiates nadph oxidase-derived ROS and fermentation-dependent acid stress to kill s. Aureus. We will develop a fluorescent-thermometer s. Aureus reporter strain to directly measure phagosomal temperature and test how heat, reactive oxygen species, and acid stress intersect to determine bacterial fate. Sepsis outcomes correlate with dysregulated temperature responses and defining how heat governs neutrophil immunity and bacterial survival will reveal temperature-sensitive therapeutic nodes. By integrating systemic and subcellular heat into infection models, this project reframes temperature as a programmable immune signal and establishes phagosomal heating as a fourth canonical stress in antimicrobial defense alongside reactive oxygen species, acidity, and hypoxia. These studies will reveal how heat governs neutrophil immunity, define microbial vulnerabilities under thermal stress, and lay the groundwork for temperature-informed strategies to improve infection outcomes. Although focused on s. Aureus, principles uncovered here will generalize to other pyogenic infections and inform the design of more faithful preclinical models.