Common concepts of immune defense

Abstract

Abstract for Section 13.1: The immune system has the challenging tasks to discriminate self from non-self, but also to discern harmless from harmful foreign antigens or entities and to attack and eliminate foreign threats. In the classical view the immune system can be divided into an innate and adaptive branch, where the innate immune system represents a quick first-line defense against pathogens, whereas the adaptive immune system is slower, but more diverse and sophisticated, able to memorize pathogens, and confer long-lasting immunity to the host. The innate immune system relies on recognition of evolutionarily conserved pathogen-associated molecular patterns (PAMPs) by innate pattern recognition molecules and receptors (PRMs and PRRs) (Degn and Thiel 2013), whereas the adaptive immune system is principally trained to recognize foreign molecules and to memorize them by highly adapted, specific receptor molecules. Abstract for Section 13.2: All organisms evolved mechanisms to protect themselves against pathogen invasion and hence possess an innate immune system. However, vertebrates have also evolved an additional strategy, the so-called adaptive immune system to further protect themselves against pathogens. In the classical view the immune system can be divided into an innate and adaptive branch of immunity with distinct function (Table 13.6) (Zinkernagel et al. 1996). In contrast to innate defense mechanisms, which occur within minutes, the adaptive immunity is slower and usually needs 4-5 days from the primary encounter with the pathogen to be activated. One hallmark of adaptive immunity is the generation of immunological memory enabling the host to remember pathogens for years. As a consequence, the host can respond to a subsequent encounter stronger, very specifically and immediately. Another hallmark of the adaptive immune system is its high antigen-diversity. This is reached by the random a priori generation of a seemingly unlimited repertoire of antigen receptors with different specificities, in contrast to the innate immune cells with a limited number of pathogen recognition receptors.