To understand the cellular and molecular pathways that regulate dynamic immune responses, we develop chemical strategies that enable the precise control of host immune responses through the inhibition or activation of specific immune cell functions in real time. We have achieved this feat by designing synthetic, small-molecule Photo-activatable Immune Modulators (PIMs) that are selectively delivered to target disease-relevant immune cells, with spatial and temporal precision provided by light illumination. Collectively, our PIMs represent a promising strategy to control and therefore understand immune responses in a dynamic, targeted manner while avoiding off-target effects to the surrounding cells and tissues. We are currently applying this synthetic immunology approach to understand inflammatory pathways during host immune responses.