Blood feeding induces hemocyte proliferation and activation in the African malaria mosquito, Anopheles gambiae Giles

Abstract

Malaria is a global public health problem, especially in sub-Saharan Africa, where the mosquito Anopheles gambiae Giles serves as the major vector for the protozoan Plasmodium falciparum Welch. One determinant of malaria vector competence is the mosquito's immune system. Hemocytes are a critical component as they produce soluble immune factors that either support or prevent malaria parasite development. However, despite their importance in vector competence, understanding of their basic biology is just developing. Applying novel technologies to the study of mosquito hemocytes, we investigated the effect of blood meal on hemocyte population dynamics, DNA replication and cell cycle progression. In contrast to prevailing published work, the data presented here demonstrate that hemocytes in adult mosquitoes continue to undergo low basal levels of replication. In addition, blood ingestion caused significant changes in hemocytes within 24 h. Hemocytes displayed an increase in cell number, size, granularity and Ras-MAPK signaling as well as altered cell surface moieties. As these changes are well-known markers of immune cell activation in mammals and Drosophila melanogaster Meigen, we further investigated whether a blood meal changes the expression of hemocyte-derived immune factors. Indeed, hemocytes 24 h post-blood meal displayed higher levels of critical components of the complement and melanization immune reactions in mosquitoes. Taken together, this study demonstrates that the normal physiological process of a blood meal activates the innate immune response in mosquitoes. This process is likely in part regulated by Ras-MAPK signaling, highlighting a novel mechanistic link between blood feeding and immunity.

Hemocyte differentiation mediates the mosquito late-phase immune response against Plasmodium in Anopheles gambiae

“…4C). In GFP-silenced mosquitoes fed with the noninvasive MAOP parasite, ∼25% of the perfused hemocytes incorporated the EdU label, similar to previous reports that demonstrated that blood feeding promotes hemocyte proliferation (19,23). When GFP-silenced mosquitoes were fed with wild-type parasites, ookinete traversal triggered a significant increase in EdU-labeled hemocytes, but this increase was abrogated by LL3 silencing (Fig.…”

“…Hemocytes appear to be the primary phagocytic cells that eliminate bacterial pathogens (29) and are thought to produce several hemolymph components involved in pathogen recognition and immune clearance (4,30). Evidence suggests that hemocytes undergo proliferation and an increase in overall hemocyte numbers in response to a blood meal (19,23), as well as aggregate in response to immune challenge (24). Following a Plasmodium-infected blood meal, mosquito hemocyte transcripts respond specifically to parasite infection, suggesting that hemocytes may have an integral role in modulating mosquito immunity (22,31).…”

“…EdU assays were performed in GFP-or LL3-silenced mosquitoes with the Click-iT EdU Alexa Fluor 594 Imaging kit (Invitrogen) similar to the procedures previously described (19). Approximately 18 h after infection with MAOP or wild-type P. berghei (corresponding to the onset of ookinete invasion), mosquitoes were injected with 20 μM EdU in PBS and allowed to recover under standard insectary conditions.…”

“…S1). Staining with FITC-conjugated wheat germ agglutinin (WGA) was used to identify hemocytes (18,19). Minimal levels of LL3 were detected in hemocytes from naïve or MAOP-infected mosquitoes.…”

The effect of Beauveria bassiana infection on cell mediated and humoral immune response in house fly, Musca domestica L.

“…The immune system relies upon the actions of several types of immune cells called hemocytes, which are primary regulators of these immune responses (Tsakas and Marmaras 2010;Bhikshapati et al 2012). Hemocytes kill pathogens either by phagocytosis, encapsulation, production of free radicals of nitrogen and oxygen, or by the production of soluble antimicrobial factors (Rodrigues et al 2010;Bryant and Michel 2014). The immune system of insect identifies invading microorganism using pattern recognition receptors (PRRs) encoded on their germ line, which is then countered by both humoral and cellular reaction ( González-Chávez et al 2009).…”