Physiology and Pathology of Innate Immune Response Against Pathogens

Pathogen infections are recognized by the immune system, which consists of two types of responses: an innate immune response and an antigen-specific adaptive immune response. The innate response is characterized by being the first line of defense that occurs rapidly in which leukocytes such as neutrophils, monocytes, macrophages, eosinophils, mast cells, dendritic cells, etc., are involved. These cells recognize the pathogen-associated molecular patterns (PAMPs), which have been evolutionarily conserved by the diversity of microorganisms that infect humans. Recognition of these pathogen-associated molecular patterns occurs through pattern recognition receptors such as Toll-like receptors and some other intracellular receptors such as nucleotide oligomerization domain (NOD), with the aim of amplifying the inflammation and activating the adaptive cellular immune response, through the antigenic presentation. In the present chapter, we will review the importance of the main components involved in the innate immune response, such as different cell types, inflammatory response, soluble immune mediators and effector mechanisms exerted by the immune response against bacteria, viruses, fungi, and parasites; all with the purpose of eliminating them and eradicating the infection of the host.