A Protocol for Collecting and Staining Hemocytes from the Yellow Fever Mosquito Aedes aegypti
Summary
A simplified yet accurate method to collect and stain mosquito hemocytes is described. Our method combines the simplicity of perfusion with the accuracy of high injection techniques to isolate clean preparations of hemocytes in Aedes mosquitoes. This method facilitates studies requiring knowledge of the types of hemocytes and their abundance.
Abstract
Mosquitoes are vectors for a number of disease-causing pathogens such as the yellow fever virus, malaria parasites and filarial worms. Laboratories are investigating anti-pathogen components of the innate immune system in disease vector species in the hopes of generating transgenic mosquitoes that are refractory to such pathogens1, 2. The innate immune system of mosquitoes consists of several lines of defense 3. Pathogens that manage to escape the barrier imposed by the epithelium-lined mosquito midgut 4 enter the hemolymph and encounter circulating hemocytes, important cellular components that encapsulate and engulf pathogens 5, 6. Researchers have not found evidence for hematopoietic tissues in mosquitoes and current evidence suggests that the number of hemocytes is fixed at adult emergence and numbers may actually decline as the mosquito ages 7. The ability to properly collect and identify hemocytes from medically important insects is an essential step for studies in cellular immunity. However, the small size of mosquitoes and the limited volume of hemolymph pose a challenge to collecting immune cells.
Two established methods for collecting mosquito hemocytes include expulsion of hemolymph from a cut proboscis 8, and volume displacement (perfusion), in which saline is injected into the membranous necklike region between the head and thorax (i.e., cervix) and the perfused hemolymph is collected from a torn opening in a distal region of the abdomen 9, 10. These techniques, however, are limited by low recovery of hemocytes and possible contamination by fat body cells, respectively 11. More recently a method referred to as high injection/recovery improved recovery of immunocytes by use of anticoagulant buffers while reducing levels of contaminating scales and internal tissues 11. While that method allows for an improved method of collecting and maintaining hemocytes for primary culture, it entails a number of injection and collecting steps that are not necessary if the downstream goal is to collect, fix and stain hemocytes for diagnostics. Here, we demonstrate our method of collecting mosquito hemolymph that combines the simplicity of perfusion, using anticoagulant buffers in place of saline solution, with the accuracy of high injection techniques to isolate clean preparations of hemocytes in Aedes mosquitoes.
Protocol
Discussion
The hemocyte collection method described here is modified from previously published methods and allows one to isolate clean preparations of hemocytes from Aedes mosquitoes with fewer steps. While our particular interest lies in characterizing hemocyte populations in Aedes mosquitoes, we believe this technique can be applied to other mosquito groups after initial trials are conducted to determine proper injection volumes. Our protocol uses anticoagulant buffers in place of saline solution and yield…
Divulgations
The authors have nothing to disclose.
Acknowledgements
Authors would like to thank John Frey and Ben Peterson for mosquito rearing. We also thank Christine Davis and Gary Radice for help with hemocyte micrographs. This research was funded by University of Richmond Arts & Science summer fellowship to A. A. Qayum and faculty grant to A. Telang.
Materials
| Name of the reagent | Company | Catalogue number | Comments (optional) |
|---|---|---|---|
| Schneider’s Medium | Sigma-Aldrich | S0146 | |
| Fetal bovine serum | Sigma-Aldrich | F0643 | |
| Hema3 stain kit | Fisher | 123-869 | |
| Glass needles (borosilicate with filament) |
Sutter Instrument | BF100-78-10 | 1.0mm O.D. and 0.78mm I.D. |
| Needle puller | Sutter Instruments | Model P-87 | |
| MicroInjector | Tritech Research | MINJ-PD | |
| Needle holder | Tritech Research | MINJ-4 |
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