Abstract
Invertebrates are becoming more popular models for research on the immune system. The innate immunity possessed by insects shows both structural and functional similarity to the resistance displayed by mammals, and many processes occurring in insect hemocytes are similar to those that occur in mammals. The humoral immune response in insects acts by melanization, clotting and the production of reactive oxygen species and antimicrobial peptides, while the cellular immunity system is based on nodulation, encapsulation and phagocytosis. An increasingly popular insect model in biological research is Galleria mellonella, whose larvae are sensitive to infection by the entomopathogenic fungus Conidiobolus coronatus, which can also be dangerous to humans. One group of factors that modulate the response of the immune system during infection in mammals are heat shock proteins (HSPs). The aim of this study was to investigate whether infection by C. coronatus in G. mellonella hemolymph is accompanied by an increase of HSP90, HSP70, HSP60 and HSP27. Larvae (five-day-old last instar) were exposed for 24 hours to fully-grown and sporulating fungus. Hemolymph was collected either immediately after termination of exposure (F24) or 24 hours later (F48). The concentration of the HSPs in hemolymph was determined using ELISA. Immunolocalization in hemocytes was performed using fluorescence microscopy and flow cytometry. HSP90, HSP70, HSP60 and HSP27 were found to be present in the G. mellonella hemocytes. HSP60 and HSP90 predominated in healthy insects, with HSP70 and HSP27 being found in trace amounts; HSP60 and HSP27 were elevated in F24 and F48, and HSP90 was elevated in F48. The fungal infection had no effect on HSP70 levels. These findings shed light on the mechanisms underlying the interaction between the innate insect immune response and entomopathogen infection. The results of this innovative study may have a considerable impact on research concerning innate immunology and insect physiology.
Highlights
Over the past decades, immunological studies have tended to favor the use of murine and rat models
The effects of C. coronatus infection on the amounts of four heat shock proteins (HSPs) (90, 70, 60, and 27) in hemocytes were examined in three groups of G. mellonella larvae
All samples were subjected to examination by fluorescence microscopy, flow cytometry and ELISA
Summary
Immunological studies have tended to favor the use of murine and rat models. As the use of such animals is expensive and laborious, and large numbers of animals have to be maintained to obtain statistically relevant data, there is a growing need for other models such as those based on invertebrates [1,2,3,4]. In contrast to many other alternative invertebrate models, they can grow in a wide temperature range (18–37 ̊C) [7,8,9,10]. This feature is useful in immunological research because it allows to conduct tests at a temperature of 37 ̊C prevailing in the body of mammals
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