Petter Brodin, an immunologist from the Karolinska Institute, dives into the fascinating world of immune responses in trans-men undergoing testosterone therapy. He discusses how testosterone levels significantly affect immune cell populations and the intricate relationship between hormones and immunity. Brodin emphasizes the importance of careful monitoring of gender-affirming treatments and explores the complexities of studying human immunology compared to traditional models. His insights shed light on the evolutionary aspects of immune regulation, creating a rich dialogue around gender dynamics and health.