A protocol for collecting and staining hemocytes from the yellow fever mosquito Aedes aegypti

Insights from the shotgun-based proteomics analysis of Biomphalaria glabrata

Biomphalaria glabrata is an important host in the transmission of human schistosomiasis in the Caribbean and South America. Therefore, it is of interest to analyse the proteome data of Biomphalaria glabrata hemolymph to identify immunity related proteins in host-pathogen relationship. We used shotgun proteomic and bioinformatic analyses of the non-depleted and depleted [0.5 and 0.75% Trifluoroacetic acid (TFA) depletion] hemolymph of B. glabrata (LE strain). Analysis showed 148 proteins from the hemolymph. 148 were obtained from the 0.5% TFA-depleted sample. 62 proteins follow this from the 0.75% TFA-depleted sample. However, only 59 were found from non-depleted hemolymph. A number of proteins were identified from the hemolymph of this schistosomiasis snail vector linked to immunity related functions. This provides insights to the understanding of schistosome-snail interaction.

Mosquito age and avian malaria infection

Background

The immune system of many insects wanes dramatically with age, leading to the general prediction that older insects should be more susceptible to infection than their younger counterparts. This prediction is however challenged by numerous studies showing that older insects are more resistant to a range of pathogens. The effect of age on susceptibility to infections is particularly relevant for mosquitoes given their role as vectors of malaria and other diseases. Despite this, the effect of mosquito age on Plasmodium susceptibility has been rarely explored, either experimentally or theoretically.

Methods

Experiments were carried out using the avian malaria parasite Plasmodium relictum and its natural vector in the field, the mosquito Culex pipiens. Both innate immune responses (number and type of circulating haemocytes) and Plasmodium susceptibility (prevalence and burden) were quantified in seven- and 17-day old females. Whether immunity or Plasmodium susceptibility are modulated by the previous blood feeding history of the mosquito was also investigated. To ensure repeatability, two different experimental blocks were carried out several weeks apart.

Results

Haemocyte numbers decrease drastically as the mosquitoes age. Despite this, older mosquitoes are significantly more resistant to a Plasmodium infection than their younger counterparts. Crucially, however, the age effect is entirely reversed when old mosquitoes have taken one previous non-infected blood meal.

Conclusions

The results agree with previous studies showing that older insects are often more resistant to infections than younger ones. These results suggest that structural and functional alterations in mosquito physiology with age may be more important than immunity in determining the probability of a Plasmodium infection in old mosquitoes. Possible explanations for why the effect is reversed in blood-fed mosquitoes are discussed. The reversal of the age effect in blood fed mosquitoes implies that age is unlikely to have a significant impact on mosquito susceptibility in the field.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0912-z) contains supplementary material, which is available to authorized users.

Use of Galleria mellonella as a model organism to study Legionella pneumophila infection

Legionella pneumophila, the causative agent of a severe pneumonia named Legionnaires' disease, is an important human pathogen that infects and replicates within alveolar macrophages. Its virulence depends on the Dot/Icm type IV secretion system (T4SS), which is essential to establish a replication permissive vacuole known as the Legionella containing vacuole (LCV). L. pneumophila infection can be modeled in mice however most mouse strains are not permissive, leading to the search for novel infection models. We have recently shown that the larvae of the wax moth Galleria mellonella are suitable for investigation of L. pneumophila infection. G. mellonella is increasingly used as an infection model for human pathogens and a good correlation exists between virulence of several bacterial species in the insect and in mammalian models. A key component of the larvae's immune defenses are hemocytes, professional phagocytes, which take up and destroy invaders. L. pneumophila is able to infect, form a LCV and replicate within these cells. Here we demonstrate protocols for analyzing L. pneumophila virulence in the G. mellonella model, including how to grow infectious L. pneumophila, pretreat the larvae with inhibitors, infect the larvae and how to extract infected cells for quantification and immunofluorescence microscopy. We also describe how to quantify bacterial replication and fitness in competition assays. These approaches allow for the rapid screening of mutants to determine factors important in L. pneumophila virulence, describing a new tool to aid our understanding of this complex pathogen.

A simple protocol for extracting hemocytes from wild caterpillars

Insect hemocytes (equivalent to mammalian white blood cells) play an important role in several physiological processes throughout an insect's life cycle. In larval stages of insects belonging to the orders of Lepidoptera (moths and butterflies) and Diptera (true flies), hemocytes are formed from the lymph gland (a specialized hematopoietic organ) or embryonic cells and can be carried through to the adult stage. Embryonic hemocytes are involved in cell migration during development and chemotaxis regulation during inflammation. They also take part in cell apoptosis and are essential for embryogenesis. Hemocytes mediate the cellular arm of the insect innate immune response that includes several functions, such as cell spreading, cell aggregation, formation of nodules, phagocytosis and encapsulation of foreign invaders. They are also responsible for orchestrating specific insect humoral defenses during infection, such as the production of antimicrobial peptides and other effector molecules. Hemocyte morphology and function have mainly been studied in genetic or physiological insect models, including the fruit fly, Drosophila melanogaster, the mosquitoes Aedes aegypti and Anopheles gambiae and the tobacco hornworm, Manduca sexta. However, little information currently exists about the diversity, classification, morphology and function of hemocytes in non-model insect species, especially those collected from the wild. Here we describe a simple and efficient protocol for extracting hemocytes from wild caterpillars. We use penultimate instar Lithacodes fasciola (yellow-shouldered slug moth) (Figure 1) and Euclea delphinii (spiny oak slug) caterpillars (Lepidoptera: Limacodidae) and show that sufficient volumes of hemolymph (insect blood) can be isolated and hemocyte numbers counted from individual larvae. This method can be used to efficiently study hemocyte types in these species as well as in other related lepidopteran caterpillars harvested from the field, or it can be readily combined with immunological assays designed to investigate hemocyte function following infection with microbial or parasitic organisms.

A quantitative assay for the juvenile hormones and their precursors using fluorescent tags

BACKGROUND

The juvenile hormones (JHs) are sesquiterpenoid compounds that play a central role in insect reproduction, development and behavior. The lipophilic nature of JHs and their precursors, in conjunction with their low concentration in tissues and susceptibility to degradation had made their quantification difficult. A variety of methods exist for JH quantification but few can quantify on the femtomole range. Currently applied methods are expensive and time consuming. In the present study we sought to develop a novel method for accurate detection and quantification of JHs and their precursors.

METHODS

A sensitive and robust method was developed to quantify the precursor, farnesoic acid (FA) and juvenile hormone III (JH III) in biological samples. The assay is based on the derivatization of analytes with fluorescent tags, with subsequent analysis by reverse phase high performance liquid chromatography coupled to a fluorescent detector (HPLC-FD). The carboxyl group of FA was derivatized with 4-Acetamido-7-mercapto-2,1,3-benzoxadiazole (AABD-SH). Tagging the epoxide group of JH III required a two-step reaction: the opening of the epoxide ring with sodium sulfide and derivatization with the fluorescent tag 4-(N,N-Dimethylaminosulfonyl)-7-(N-chloroformylmethyl-N-methylamino)-2,1,3-benzoxadiazole (DBD-COCl).

CONCLUSIONS

The method developed in the present study showed high sensitivity, accuracy and reproducibility. Linear responses were obtained over the range of 10-20 to 1000 fmols. Recovery efficiencies were over 90% for JH III and 98% for FA with excellent reproducibility.

SIGNIFICANCE

The proposed method is applicable when sensitive detection and accurate quantification of limited amount of sample is needed. Examples include corpora allata, hemolymph and whole body of female adult Aedes aegypti and whole body Drosophila melanogaster. A variety of additional functional groups can be targeted to add fluorescent tags to the remaining JH III precursors.