C5a anaphylatoxin chemotactic receptor 1 (C5aR1) is a protein that in humans is encoded by the C5AR1 gene. The C5aR1 protein functions as a receptor for the toxic compound ciclosporin, which binds to and activates this protein. This activation leads to the release of other mediators, including cytokines and prostaglandins, which can contribute to inflammation and allergic responses.