Morphological and Ultrastructural Characterization of Hemocytes in an Insect Model, the Hematophagous Dipetalogaster maxima (Hemiptera: Reduviidae)

Abstract

Hemocytes, the cells present in the hemolymph of insects and other invertebrates, perform several physiological functions, including innate immunity. The current classification of hemocyte types is based mostly on morphological features; however, divergences have emerged among specialists in triatomines, the insect vectors of Chagas’ disease (Hemiptera: Reduviidae). Here, we have combined technical approaches in order to characterize the hemocytes from fifth instar nymphs of the triatomine Dipetalogaster maxima. Moreover, in this work we describe, for the first time, the ultrastructural features of D. maxima hemocytes. Using phase contrast microscopy of fresh preparations, five hemocyte populations were identified and further characterized by immunofluorescence, flow cytometry and transmission electron microscopy. The plasmatocytes and the granulocytes were the most abundant cell types, although prohemocytes, adipohemocytes and oenocytes were also found. This work sheds light on a controversial aspect of triatomine cell biology and physiology setting the basis for future in-depth studies directed to address hemocyte classification using non-microscopy-based markers.

An Efficient and Simple Method for Collecting Haemolymph of Cerambycidae (Insecta: Coleoptera) Adults

“…Haemolymph smears collected by the tearing method showed more fat cells in the field of view ( Figure 4 B,E,H). The haemolymph smear obtained by double centrifugation showed more blood coagulation after staining and greater heterogeneity ( Figure 4 C,F,H) [ 25 ].…”

Does Bacillus thuringiensis Affect the Stress and Immune Responses of Rhynchophorus ferrugineus Larvae, Females, and Males in the Same Way?

“…In particular, spherulocytes are involved in the coagulation process and are fragile cells that break easily during sampling procedures [ 54 ]. Prohemocytes have features of precursor cells which are able to differentiate into other hemocyte categories and are the smallest cells in hemolymph [ 54 , 55 ]. Their role and modulation after Bt treatment in R. ferrugineus needs to be more thoroughly investigated.…”

Immune Reactions of Vector Insects to Parasites and Pathogens

“…The haemocytes of triatomines have been described in detail by some authors although there can be some variations from species to species and according to the preparation technique used [ 112 ]. In most studies, prohaemocytes, plasmatocytes, granular cells, oenocytoids and adipohaemocytes are recognised [ 112 , 113 ] with giant cells and cystocytes also identified in R. prolixus and Dipetalogaster maxima [ 112 , 113 ] ( Table 2 ). The more recent study of the haemocytes of D. maxima also used immunofluorescence and flow cytometry analysis and seemed to confirm the classification of cell types described above.…”

“…Coagulation of insect haemolymph occurs in most studies of different species and is an essential process limiting the excess loss of haemolymph and preventing the entry of parasites and pathogens. Haemolymph coagulation has been reported in mosquitoes [ 114 ], triatomines [ 112 , 113 ], blackflies [ 104 ], tsetse flies [ 12 ] and lice [ 115 ]. It basically occurs in two phases, initially involving the cross-linking of clot components from the plasma and haemocytes and depending on transaminase activity followed by phenoloxidase hardening and melanising the soft clot material [ 116 ].…”