Functional exhaustion of T lymphocytes in chronic toxoplasmosis

One of the most characteristic features of many intracellular parasite infections is their chronicity indicating that the host immune system is not capable of eradicating the pathogen. Toxoplasma gondii is the most successful parasite worldwide, infecting an extraordinarily broad range of hosts (endothermic animals and humans) and almost all cell types. Recent studies have revealed that in late chronic toxoplasmosis CD8⁺ T lymphocytes become progressively exhausted and this dysfunction is suggested to be responsible for the reactivation of latent infection, which may result in a life-threatening disease in immunocompromised individuals (e.g. neurotoxoplasmosis in AIDS patients). The article presents selected aspects of a new paradigm – T cell exhaustion phenomenon – a progressive dysfunction over time, which makes the host unable to control intracellular pathogen infections or tumours.