The study focuses on so-called macrophages. These immune cells, among other things, break down old red blood cells and store iron nanoparticles in the process. This stored iron gives the cells magnetic properties. The researchers observed that carrier pigeons exhibited impaired orientation under overcast skies when the function of these iron-rich immune cells was compromised. When the sun was visible, the birds continued to find their way back and apparently used visual cues for orientation.
“Our results reveal a previously unknown mechanism of magnetic perception in animals,” says Prof. Christian Kurts, Director of the Institute for Molecular Medicine and Experimental Immunology at the UKB and a member of the ImmunoSensation3 Cluster of Excellence as well as the Transdisciplinary Research Area (TRA) "Life and Health" at the University of Bonn. “The fact that immune cells could act as sensors for magnetic fields surprised even us.”
To track down the magnetically active cells, the team examined various organs of the animals, including the eyes, beak, brain, liver, and spleen. The liver, in particular, showed a high concentration of superparamagnetic iron particles. Further analyses identified macrophages as the key cell population.
“Of all the tissues examined, the liver exhibited the strongest magnetic properties,” explains lead author Dr. Clivia Lisowski of the Institute of Molecular Medicine and Experimental Immunology at the UKB. “Our data provide the first concrete evidence of how the Earth’s magnetic field might be detected within the body and transmitted to the brain.”
Electron microscopic examinations also showed that the iron-rich macrophages are located in the immediate vicinity of nerve fibers. This suggests that magnetic information could be transmitted from there to the nervous system.
“Animal navigation is one of the most fascinating phenomena in nature,” says Prof. Dr. Martin Wikelski, Director of the Department of Animal Migration at the Max Planck Institute for Behavioral Biology. “If it is confirmed that immune cells are involved, this would represent a fundamental paradigm shift in our understanding of orientation in the animal kingdom.”
The study thus combines insights from immunology, physics, and behavioral biology and offers a new approach to explaining animal navigation. The researchers suspect that similar mechanisms may also occur in other animal species.