Key concepts in immunology.

Vertebrates have developed systems of immune defence enabling them to cope with the constant threat posed by environmental pathogens. The mammalian immune system represents a multilayered defence system comprising both innate and adaptive immune responses, characterized by the increasing complexity of their antigen-recognition systems. The discovery of the intimate relationship between innate and adaptive responses has paved the way to a novel understanding of the basic mechanisms governing the regulation of an immune response. The purpose of the present review is to briefly describe the basic immunological concepts that constitute the founding principles of modern vaccinology in humans. 2010 Elsevier Ltd. All rights reserved.