Insects are the most speciose group of animals. As a phylogenetic group, the class Insecta diverged from other pancrustaceans between 400 and 500 million years ago, and its members vary greatly in size, ecology, and lifestyle. Regardless of these differences, all insects share many commonalities. One of these is their constant contact with infectious agents.

When pathogens enter the hemocoel of an insect they immediately confront at least two major forces: (1) immune-responses with the capacity to destroy pathogens, and (2) circulatory currents that control or affect the movement or migration of pathogens. Although a significant amount of work has been directed toward understanding insects’ immune-responses, and to a lesser extent the anatomy of the circulatory system, it has not been until recently that researchers have assessed how circulatory currents affect immune-responses. This review summarizes our current understanding of the immune and circulatory systems of insects, and describes how these two systems interact during the course of an infection. Furthermore, this review also compares the immune and circulatory systems of insects to that of crustaceans, and concludes with a description of how the immune and circulatory systems of crustaceans also interact during the course of an infection.

This review article is part of a special issue of Integrative and Comparative Biology, titled “Comparative Physiology of the Pancrustacea”.  This issue is a follow-up of a symposium held earlier this year at the annual meeting of the Society for Integrative and Comparative Biology.

Article citation:

Hillyer, J.F. 2015. Integrated immune and cardiovascular function in Pancrustacea: Lessons from the insects. Integrative & Comparative Biology. DOI: 10.1093/icb/icv021

(Pubmed) (See it in ICB) (Email me for a pdf copy)

Graphical abstract:

Article abstract:

When pathogens invade the insect hemocoel (body cavity) they immediately confront two major forces: immune-responses and circulatory currents. The immune response is mediated by circulating and sessile hemocytes, the fat body, the midgut, and the salivary glands. These tissues drive cellular and humoral immune processes that kill pathogens via phagocytosis, melanization, lysis, encapsulation, and nodulation. Moreover, immune-responses take place within a three-dimensional and dynamic space that is governed by the forces of the circulatory system. The circulation of hemolymph (insect blood) is primarily controlled by the wave-like contraction of a dorsal vessel, which is a muscular tube that extends the length of the insect and is divided into a thoracic aorta and an abdominal heart. Distributed along the heart are valves, called ostia, that allow hemolymph to enter the vessel. Once inside the heart, hemolymph is sequentially propelled to the anterior and to the posterior of the body. During an infection, circulatory currents sweep small pathogens to all regions of the body. As they circulate, pathogens encounter immune factors of the insect that range from soluble cytotoxic peptides to phagocytic hemocytes. A prominent location for these encounters is the surface of the heart. Specifically, periostial hemocytes aggregate in the extracardiac regions that flank the heart's ostia (the periostial regions) and phagocytoze pathogens in areas of high flow of hemolymph. This review summarizes the biology of the immune and circulatory systems of insects, including how these two systems have co-adapted to fight infection. This review also compares the immune and circulatory systems of insects to that of crustaceans, and details how attachment of hemocytes to cardiac tissues and the biology of the lymphoid organ demonstrate that dynamic interactions between the immune and circulatory systems also occur in lineages of crustaceans.