Why Infections Make Us Sick: Host Defenses of the Brain–Immune Axis

Host defense systems are essential for life across diverse species. In humans and other mammals, innate and adaptive immunity enable the detection, elimination and memory of encounters with pathogens at the cellular and tissue scales. At the organism scale, bidirectional communication between the immune system and the brain generates changes in physiology and behavior — such as fever, lethargy and anorexia — collectively known as sickness behavior.

In this Presidential Lecture, Zuri Sullivan will explore sickness behavior through the lens of host defense. By framing sickness as immunity operating at the organismal scale, she will explore potential parallels with cellular and tissue immunity to define new questions about the mechanisms and consequences of brain–immune system communication: Does the brain differentiate between different kinds of pathogens? What molecular signals and cellular effectors lead to sickness in different contexts? When is sickness adaptive for the host, the pathogen, or neither? These discussions aim to link sickness to broader themes of host defense — a fundamental challenge for biological systems.

Sullivan is a member of the Whitehead Institute for Biomedical Research, an assistant professor of biology at the Massachusetts Institute of Technology, and a Howard Hughes Medical Institute Hanna Gray Faculty Fellow. She earned her A.B. in molecular and cellular Biology at Harvard University, a Ph.D. in immunobiology from Yale University and completed postdoctoral training in neuroscience at Harvard University. Sullivan joined the Whitehead Institute in January 2026, where her lab studies how interactions between the brain and the immune system promote host defense at the organism scale.