We teach medical students Physiology. They then take a separate course Immunology and the two disciplines rarely overlap. However, it is becoming clear that immune cells integrate into an organ become resident and perform critical functions to maintain homeostasis. I study what these cells do under homeostasis by visualizing their behaviour. Alveolar macrophages remove debris and surfactant from alveoli and without this function oxygen exchange is impaired. Similarly, pruning of neurons and removing old platelets and red blood cells are all part of the daily function of the immune system. But how does a cell in the liver know it is in the liver and not in the lung? What are the communication pathways that inform immune cells where they are? What happens when the environment changes due to our lifestyle insults (drinking, smoking, surgical interventions) and how do these lifestyle-associated molecular patterns (LAMPs) affect the immune cells? Can the immune cells recover from these insults? I will discuss some of these issues using various modalities of imaging to understand how the immune system contributes to physiology and how it responds to perturbation.