Specialized Immune Systems of Animals

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 and secreted.

Keywords: 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.