The Evolution of Immune Sensitivity under Immunopathological and Autoimmune Costs

Hosts with high immune sensitivity benefit from rapid recovery but suffer multiple costs thereof. We distinguish between immunopathological costs due to collateral damage and autoimmune costs due to false positives against self. Selection on sensitivity follows different trajectories depending on the cost nature and the overlap degree between host- and parasitic molecular signatures. Increased parasite virulence selects for higher immune sensitivity under immunopathological costs but low sensitivity when the costs are autoimmune, contradicting previous theoretical results. Longer lifespans of the host select for low sensitivity under immunopathology to avoid accumulated tissue damage. Under autoimmune costs, hosts with a short lifespan cannot afford to shorten it further due to autoimmunity and evolve lower immune sensitivity. Longer lifespan selects for high or low sensitivity depending on the presence of immune memory. These results extend our understanding of selection on immune sensitivity and help explain phenomena like the cytokine shock and chronic infections.