A tiny invader, perhaps a virus or a microbe, enters the body, and our ancient immune system responds. But how does it know what kind of invader has landed? And once it knows, how does it decide what kind of immune response it should launch?
Itâ€™s the innate immune systemâ€™s job to recognize the first signs of infectionâ€”that is, the moment a pathogen enters the body. â€œIn a sense they act as smoke detectors if you will,â€ says Pulendran. â€œLittle alarms.â€