In a Drosophila larva in Barcelona’s IRB laboratories, green-glowing macrophages nestle beside the red-lit prothoracic gland—a tiny anatomical embrace that holds a big clue about how the immune system helps growing bodies adapt to poor nutrition. Led by Dr. Sergio Juárez-Carreño and Dr. Marco Milán, a new study reveals that immune cells don’t just fight invaders—they also act as vital interpreters of dietary stress, adjusting the very pace of development when sugar levels soar. This discovery reshapes our understanding of how bodies navigate the challenges of modern diets, especially during sensitive growth periods.
While high-sugar diets are known to trigger insulin resistance and chronic inflammation, their impact on developmental timing has been less clear. Using Drosophila melanogaster—a powerful model for studying growth and metabolism—the team uncovered a previously unknown dialogue between immune cells and hormone-producing tissues. When larvae consume excess sugar, macrophages produce a protein called Dpp, the fly equivalent of human BMP2/4. This signal travels to the prothoracic gland and suppresses the production of ecdysone, the steroid hormone that triggers metamorphosis. The result? A developmental pause—extending the larval stage from the usual five days to six or seven.
This delay isn’t a malfunction—it’s a survival strategy. When the researchers blocked Dpp signaling, larvae failed to fully compensate for the sugar-rich diet and emerged as smaller adults. This shows that the immune system’s intervention isn’t just reactive; it’s protective, giving the organism extra time to grow under suboptimal conditions. "The immune system does not only respond to infections or damage. It also acts as an internal surveillance system, capable of adjusting the pace of development when nutritional conditions are suboptimal," says Milán, an ICREA researcher and head of the Development and Growth Control laboratory at IRB Barcelona.
The implications stretch beyond fruit flies. BMP proteins are evolutionarily conserved, meaning similar mechanisms could be at play in mammals—including humans. While the study doesn’t prove the same pathway exists in people, it opens a compelling line of inquiry: could childhood obesity or metabolic disorders subtly alter hormonal development through immune signaling? As diets high in sugar become more common worldwide, understanding these hidden connections between immunity, nutrition, and growth becomes increasingly urgent.
Looking ahead, Juárez-Carreño, now a group leader at the Andalusian Center for Developmental Biology, will explore how early sugar exposure affects adult health—a critical question in an era of rising metabolic disease. This work reminds us that our bodies are not just reacting to what we eat, but constantly recalibrating in real time, with immune cells serving as both guardians and conductors of development.