Insect immunology and hematopoiesis

Abstract

Insects combat infection by mounting powerful immune responses that are mediated by hemocytes, the fat body, the midgut, the salivary glands and other tissues. Foreign organisms that have entered the body of an insect are recognized by the immune system when pathogen-associated molecular patterns bind host-derived pattern recognition receptors. This, in turn, activates immune signaling pathways that amplify the immune response, induce the production of factors with antimicrobial activity, and activate effector pathways. Among the immune signaling pathways are the Toll, Imd, Jak/Stat, JNK, and insulin pathways. Activation of these and other pathways leads to pathogen killing via phagocytosis, melanization, cellular encapsulation, nodulation, lysis, RNAi-mediated virus destruction, autophagy and apoptosis. This review details these and other aspects of immunity in insects, and discusses how the immune and circulatory systems have co-adapted to combat infection, how hemocyte replication and differentiation takes place (hematopoiesis), how an infection prepares an insect for a subsequent infection (immune priming), how environmental factors such as temperature and the age of the insect impact the immune response, and how social immunity protects entire groups. Finally, this review highlights some underexplored areas in the field of insect immunobiology.

Brain gene expression analyses in virgin and mated queens of fire ants reveal mating‐independent and socially regulated changes

“…Some ant species exhibit an increased immune response and become more pathogen‐tolerant after mating (Castella, Christe, & Chapuisat, ; Galvez & Chapuisat, ). In insect immune response, insect hemocytes and antimicrobial peptides (AMPs) play important roles in defense (Hillyer, ; Viljakainen & Pamilo, ; Vlisidou & Wood, ). We found upregulated genes in queen brains representative of these pathways; astakine , a neuropeptide, likely induces hematopoiesis (Lin, Kim, Lee, Soderhall, & Soderhall, ; Lin & Soderhall, ; Lin, Soderhall, & Soderhall, ) and nc725 , which likely encodes an AMP (see below).…”

Research progress on the immune mechanism of the silkworm Bombyx mori

“…The production and deposition of melanin at the site of injury may trap and kill invading microbes. The melanization process represents a coordinating interaction involving pattern recognition receptors, serine proteases, serine and enzymes that promote melanogenesis (Hillyer, ). During melanization reactions, soluble pattern recognition proteins promote the recognition of nonself objects associated with invading microbes (Matskevich et al, ; Wang et al, ; Stokes et al, ), which triggers sequential activation of a series of serine proteases and leads to the activation of the prophenoloxidase‐activating enzyme into its active form (In‐Kwon et al, ; Tokura et al, ).…”

“…During melanization reactions, soluble pattern recognition proteins promote the recognition of nonself objects associated with invading microbes (Matskevich et al, ; Wang et al, ; Stokes et al, ), which triggers sequential activation of a series of serine proteases and leads to the activation of the prophenoloxidase‐activating enzyme into its active form (In‐Kwon et al, ; Tokura et al, ). Afterwards, inactive prophenoloxidase (Pro‐PO) is activated into PO (An et al, ; Zhen et al, ; An et al, ; Lu et al, ), which participates in the melanization process as a catalyst (Christensen et al, ; Nappi et al, ; Hillyer, ; Sanzhaeva et al, ). A schematic of the pathway associated with the silkworm melanization mechanism is provided based on existing reports (Fig.…”

Arthropod Innate Immune Systems and Vector-Borne Diseases

“…12 Hemolymph contains several types of cells, or hemocytes: (i) plasmatocytes and granulocytes, (ii) lamellocytes, and (iii) oenocytoids or crystal cells. 13 Phagocytosis, the engulfment of bacteria and other small particles, is performed by plasmatocytes ( Drosophila melanogaster ) or granulocytes ( Anopheles gambiae ). Some granulocytes facilitate agglutination, clumping pathogens and hemocytes together, or coagulation of hemolymph in response to wounding.…”