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The role of salivary and intestinal complement system inhibitors in the midgut protection of triatomines and mosquitoes.

Barros VC, Assumpção JG, Cadete AM, Santos VC, Cavalcante RR, Araújo RN, Pereira MH, Gontijo NF - PLoS ONE (2009)

Bottom Line: Both, saliva and intestinal contents from all triatomines were able to inhibit C3b deposition in the classical and alternative pathways.None of the material extracted from the intestinal cell membranes from the triatomines inhibited C3b deposition in the classical pathway.The existence of complement inhibitors may have important biological consequences which are discussed in detail.

View Article: PubMed Central - PubMed

Affiliation: Department of Parasitology, Federal University of Minas Gerais (UFMG), Belo Horizonte, Minas Gerais, Brazil.

ABSTRACT
Saliva of haematophagous arthropods contain biomolecules involved directly or indirectly with the haematophagy process, and among them are encountered some complement system inhibitors. The most obvious function for these inhibitors would be the protection of the midgut against injury by the complement. To investigate this hypothesis, Triatoma brasiliensis nymphs were forced to ingest human serum in conditions in which the protection of midgut by the inhibitors is bypassed. In these conditions, the anterior midgut epithelium was injured by the complement, causing cell death. Once some insects such as Aedes aegypti have no salivary inhibitors, we hypothesized the existence of intestinal inhibitors. The inhibitory activity was investigated in the intestine of A. aegypti as well as in the saliva and intestine of other three triatomine species (T. brasiliensis, T. infestans and Rhodnius prolixus) using an immunological method able to determine the level of deposition of some complement factors (C1q, C3b, or C4b) on the surface of complement activator molecules linked to microplates. This methodology permitted to identify which points along the activation phase of the complement cascade were inhibited. As expected, soluble contents of A. aegypti's intestine was capable to inhibit C3b deposition by the classical and alternative pathways. Saliva or soluble intestinal contents, obtained from triatomines were unable to inhibit C1q deposition by the classical pathway. C4b deposition by the classical pathway was inhibited by the intestinal contents from the three triatomines. On the other hand, only T. brasiliensis saliva inhibited C4b deposition. Both, saliva and intestinal contents from all triatomines were able to inhibit C3b deposition in the classical and alternative pathways. None of the material extracted from the intestinal cell membranes from the triatomines inhibited C3b deposition in the classical pathway. The existence of complement inhibitors may have important biological consequences which are discussed in detail.

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Protection of anterior midgut of T. brasiliensis against the complement system.A- MAC deposition onto the anterior midgut wall after normal blood ingestion, B- natural fluorescence observed on the midgut wall, C- Apparatus used for the forced feeding procedure, D- MAC deposition onto the anterior midgut wall after forced feeding of 50 µL of normal human sera, E- Increased deposition of MAC onto the anterior midgut wall after forced feeding of 50 µL of 2 fold concentrated normal human sera, F- MAC deposition onto the anterior midgut wall after forced feeding of 50 µL of inactivated 2 fold concentrated normal human sera, G- Cell death in the anterior midgut epithelium after forced feeding of 2 fold concentrated normal human serum containing propidium iodide. H- Absence of cell death after forced feeding of inactivated 2 fold concentrated normal human sera containing propidium iodide.
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pone-0006047-g001: Protection of anterior midgut of T. brasiliensis against the complement system.A- MAC deposition onto the anterior midgut wall after normal blood ingestion, B- natural fluorescence observed on the midgut wall, C- Apparatus used for the forced feeding procedure, D- MAC deposition onto the anterior midgut wall after forced feeding of 50 µL of normal human sera, E- Increased deposition of MAC onto the anterior midgut wall after forced feeding of 50 µL of 2 fold concentrated normal human sera, F- MAC deposition onto the anterior midgut wall after forced feeding of 50 µL of inactivated 2 fold concentrated normal human sera, G- Cell death in the anterior midgut epithelium after forced feeding of 2 fold concentrated normal human serum containing propidium iodide. H- Absence of cell death after forced feeding of inactivated 2 fold concentrated normal human sera containing propidium iodide.

Mentions: When fourth instar nymphs of T. brasiliensis ingested blood from human voluntaries, no marked areas in the anterior midgut (crop) were seen (Figure 1-A) except for the natural intestine fluorescence (Figure 1-B). In this case, we can attribute the absence of attack to an effective concentration of salivary and intestinal inhibitors acting together inside the anterior midgut (it is important to consider that, in triatomines, saliva is regularly ingested during a blood meal [15]). To investigate the importance of the complement inhibitors in protecting the anterior midgut, we forced the insects to ingest sera in a condition in which saliva ingestion is drastically reduced. This forced feeding procedure was accomplished by using the apparatus shown in Figure 1-C. In this condition, practically only intestinal inhibitors would be available to protect the intestinal epithelium and they were not enough to do it. The nearly absence of saliva in the forced fed nymphs was confirmed by using the salivary enzyme apyrase as a saliva tracker (Figure 2). According to Figure 1-D, the epithelium of the anterior midgut was slightly marked by MAC proteins after the forced feeding with 50 µL of normal human serum. The marking intensity increased considerably when nymphs were forced to feed the same volume of two fold concentrated sera (Figure 1-E). No marks were observed when insects were forced to ingest 50 µL of inactivated two fold concentrated human sera (Figure 1-F) except for the natural fluorescence similar to that in Figure 1-B.


The role of salivary and intestinal complement system inhibitors in the midgut protection of triatomines and mosquitoes.

Barros VC, Assumpção JG, Cadete AM, Santos VC, Cavalcante RR, Araújo RN, Pereira MH, Gontijo NF - PLoS ONE (2009)

Protection of anterior midgut of T. brasiliensis against the complement system.A- MAC deposition onto the anterior midgut wall after normal blood ingestion, B- natural fluorescence observed on the midgut wall, C- Apparatus used for the forced feeding procedure, D- MAC deposition onto the anterior midgut wall after forced feeding of 50 µL of normal human sera, E- Increased deposition of MAC onto the anterior midgut wall after forced feeding of 50 µL of 2 fold concentrated normal human sera, F- MAC deposition onto the anterior midgut wall after forced feeding of 50 µL of inactivated 2 fold concentrated normal human sera, G- Cell death in the anterior midgut epithelium after forced feeding of 2 fold concentrated normal human serum containing propidium iodide. H- Absence of cell death after forced feeding of inactivated 2 fold concentrated normal human sera containing propidium iodide.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2698215&req=5

pone-0006047-g001: Protection of anterior midgut of T. brasiliensis against the complement system.A- MAC deposition onto the anterior midgut wall after normal blood ingestion, B- natural fluorescence observed on the midgut wall, C- Apparatus used for the forced feeding procedure, D- MAC deposition onto the anterior midgut wall after forced feeding of 50 µL of normal human sera, E- Increased deposition of MAC onto the anterior midgut wall after forced feeding of 50 µL of 2 fold concentrated normal human sera, F- MAC deposition onto the anterior midgut wall after forced feeding of 50 µL of inactivated 2 fold concentrated normal human sera, G- Cell death in the anterior midgut epithelium after forced feeding of 2 fold concentrated normal human serum containing propidium iodide. H- Absence of cell death after forced feeding of inactivated 2 fold concentrated normal human sera containing propidium iodide.
Mentions: When fourth instar nymphs of T. brasiliensis ingested blood from human voluntaries, no marked areas in the anterior midgut (crop) were seen (Figure 1-A) except for the natural intestine fluorescence (Figure 1-B). In this case, we can attribute the absence of attack to an effective concentration of salivary and intestinal inhibitors acting together inside the anterior midgut (it is important to consider that, in triatomines, saliva is regularly ingested during a blood meal [15]). To investigate the importance of the complement inhibitors in protecting the anterior midgut, we forced the insects to ingest sera in a condition in which saliva ingestion is drastically reduced. This forced feeding procedure was accomplished by using the apparatus shown in Figure 1-C. In this condition, practically only intestinal inhibitors would be available to protect the intestinal epithelium and they were not enough to do it. The nearly absence of saliva in the forced fed nymphs was confirmed by using the salivary enzyme apyrase as a saliva tracker (Figure 2). According to Figure 1-D, the epithelium of the anterior midgut was slightly marked by MAC proteins after the forced feeding with 50 µL of normal human serum. The marking intensity increased considerably when nymphs were forced to feed the same volume of two fold concentrated sera (Figure 1-E). No marks were observed when insects were forced to ingest 50 µL of inactivated two fold concentrated human sera (Figure 1-F) except for the natural fluorescence similar to that in Figure 1-B.

Bottom Line: Both, saliva and intestinal contents from all triatomines were able to inhibit C3b deposition in the classical and alternative pathways.None of the material extracted from the intestinal cell membranes from the triatomines inhibited C3b deposition in the classical pathway.The existence of complement inhibitors may have important biological consequences which are discussed in detail.

View Article: PubMed Central - PubMed

Affiliation: Department of Parasitology, Federal University of Minas Gerais (UFMG), Belo Horizonte, Minas Gerais, Brazil.

ABSTRACT
Saliva of haematophagous arthropods contain biomolecules involved directly or indirectly with the haematophagy process, and among them are encountered some complement system inhibitors. The most obvious function for these inhibitors would be the protection of the midgut against injury by the complement. To investigate this hypothesis, Triatoma brasiliensis nymphs were forced to ingest human serum in conditions in which the protection of midgut by the inhibitors is bypassed. In these conditions, the anterior midgut epithelium was injured by the complement, causing cell death. Once some insects such as Aedes aegypti have no salivary inhibitors, we hypothesized the existence of intestinal inhibitors. The inhibitory activity was investigated in the intestine of A. aegypti as well as in the saliva and intestine of other three triatomine species (T. brasiliensis, T. infestans and Rhodnius prolixus) using an immunological method able to determine the level of deposition of some complement factors (C1q, C3b, or C4b) on the surface of complement activator molecules linked to microplates. This methodology permitted to identify which points along the activation phase of the complement cascade were inhibited. As expected, soluble contents of A. aegypti's intestine was capable to inhibit C3b deposition by the classical and alternative pathways. Saliva or soluble intestinal contents, obtained from triatomines were unable to inhibit C1q deposition by the classical pathway. C4b deposition by the classical pathway was inhibited by the intestinal contents from the three triatomines. On the other hand, only T. brasiliensis saliva inhibited C4b deposition. Both, saliva and intestinal contents from all triatomines were able to inhibit C3b deposition in the classical and alternative pathways. None of the material extracted from the intestinal cell membranes from the triatomines inhibited C3b deposition in the classical pathway. The existence of complement inhibitors may have important biological consequences which are discussed in detail.

Show MeSH
Related in: MedlinePlus