ABSTRACT
This chapter focuses on adaptive immune responses. An infant born with a severely defective adaptive immune system will soon die unless extraordinary measures are taken to isolate it from a host of infectious agents, including bacteria, viruses, fungi, and parasites. Adaptive immune responses eliminate or destroy invading pathogens and any toxic molecules they produce. The adaptive immune system uses multiple mechanisms to avoid damaging responses against self molecules. The innate immune system can even distinguish between different classes of pathogens and recruit the most effective form of adaptive immune response to eliminate them. Any substance capable of eliciting an adaptive immune response is referred to as an antigen. Adaptive immune responses are carried out by white blood cells called lymphocytes. Lymphocytes are responsible for the astonishing specificity of adaptive immune responses. The most remarkable feature of the adaptive immune system is that it can respond to millions of different foreign antigens in a highly specific way.
