Protection and pathology during parasite infection: IL ‐10 strikes the balance

The host response to infection requires an immune response to be strong enough to control the pathogen but also restrained, to minimize immune-mediated pathology. The conflicting pressures of immune activation and immune suppression are particularly apparent in parasite infections, where co-evolution of host and pathogen has selected many different compromises between protection and pathology. Cytokine signals are critical determinants of both protective immunity and immunopathology, and, in this review, we focus on the regulatory cytokine IL-10 and its role in protozoan and helminth infections. We discuss the sources and targets of IL-10 during parasite infection, the signals that initiate and reinforce its action, and its impact on the invading parasite, on the host tissue, and on coincident immune responses.