The aryl hydrocarbon receptor (AHR) can sense and initiate immune responses to many different infectious organisms. Here, Moura-Alves and colleagues review the role of the AHR in host–pathogen interactions and explore the therapeutic potential of targeting the AHR in the context of different infectious diseases.

Oxygen levels vary throughout the body and immune cells must adapt to these changes, both during homeostasis and in disease. Here, the authors discuss the impact of physiological subatmospheric oxygen levels (physioxia) as well as disease-related hypoxia on immune cell responses. They consider the therapeutic relevance of understanding how oxygenation affects immune responses in various diseases, including tuberculosis, COVID-19 and cancer.

Macrophages are associated with many human diseases but are challenging to study in vivo. Here, Ginhoux and colleagues discuss how iMacs — macrophages generated from induced pluripotent stem (iPS) cells — can enable disease modelling, including through the use of patient-derived iPS cells and 3D organoid co-culture systems. Ultimately, these iMac-based approaches can improve our understanding of macrophage biology in both health and disease.

Technological advances in cellular and molecular immunology are providing unprecedented new insights into evolutionary immunology. This Perspective highlights new insights into the immune systems of different vertebrate species and discusses emerging general principles of immune system function.