Expanding role of adaptive immunity
The adaptive immune system heavily invests in multilayered tolerance programs and appears overengineered for pathogen defense alone.
Depletion of adaptive immune circuits triggers widespread homeostatic breakdown even in the absence of pathogens, suggesting a central role in organismal homeostasis.
Mitochondria transfer, critical for cellular homeostasis in complex multicellular organisms, compensates for metabolic stress but introduces cellular variance and risks an immunogenic response to an organelle of bacterial ancestry.
The increasing mitochondrial mobility in complex multicellular organisms may have created selective pressure for layered surveillance and tolerance systems, which may have eventually been co-opted for pathogen defense.
https://www.cell.com/trends/immunology/fulltext/S1471-4906(26)00101-8
