ABSTRACT
The first line of defense against infection is the innate
immune system and activation occurs when a pathogen
breaches the host’s natural barriers (Fig. 16.1).1 The innate
immune system developed before the separation of vertebrates
from invertebrates and is the primary immune response for
most multicellular organisms.2 It responds instantaneously to
microbes and is composed of both soluble (the alternative
and mannan-binding lectin pathways of the complement
system, acute phase proteins, and cytokines) and cellular
elements (monocytes, macrophages, neutrophils, dendritic
cells, and natural killer cells). Careful modulation of the
innate immune system is vital to prevent either uncontrolled
microbial growth or devastating inflammatory responses with
tissue injury, vascular collapse, and multiorgan failure.
