Specialized Immune Systems of Animals
Pp. 339-379 (41)
Specialized immune systems of animals include innate and adaptive immune
cells and humoral factors. Inflammation is also a specialized systemic immune
response. Innate immune cells include professional phagocytes such as macrophages,
dendritic cells, and neutrophils, as well as natural killer (NK) cells. Adaptive immune
cells are T and B lymphocytes. Immune cells work in cooperation with humoral factors
such as the complement system, secreted pattern-recognition receptors, and antibodies.
Inflammation activates immune cells and generates fever. Acute inflammation is
beneficial, whereas chronic inflammation may lead to pathology including
atherosclerosis, type 2 diabetes, and autoimmune diseases. Recognition of pathogenassociated
molecular patterns (PAMPs) by phagocytes leads to their activation,
phagocytosis, respiratory burst producing reactive oxygen (ROS) and nitrogen (RNS)
species, and secretion of antimicrobial peptides and pro-inflammatory cytokines. NK
cells function on a different recognition principle. They express a variety of activating
receptors to endogenous molecules expressed on distressed but not healthy cells.
Engagement of these receptors triggers cytotoxic activity. NK cells also express
inhibitory receptors that bind “self” markers such as MHCI molecules, which are
expressed on all healthy cells. The balance between the engagement of activating and
inhibitory receptors determines cell fate. Complement is a humoral cascade of enzymes
that promotes chemotaxis, inflammation, and phagocytosis, as well as kills pathogens
and infected or stressed cells. The evolutionary youngest specialized adaptive immune
system consists of T and B cells, which express rearranging receptors both membrane
Adaptive immune receptors, Complement system, Fever,
Inflammation, IL1β, IL6, Inflammatory diseases, Macrophage, NOX2, NK cells,
Phagocytosis, PRR, PAMP, Respiratory burst, TNF, V(D)J recombination.
Department of Molecular Cell & Developmental Biology, University of California, Los Angeles CA, USA.