Percentage of inhibition of the complement system by saliva from <i>Triatoma brasiliensis, T. infestans</i> and <i>Rhodnius prolixus</i>.

<p>(n) = number of independent experiments performed for each treatment.</p><p>Asterisk (*) indicates statistical difference from control (P<0.05).</p><p>AP: Alternative Pathway, CP: Classical Pathway.</p

Influence of pH in the operation of the human complement system.

<p>Operation of the classical (A) and alternative (B) pathways at different pHs when compared with the control at pH 7.4 (100%).</p

Scheme of the activation phase of the complement system showing the points potentially targeted by the inhibitors.

<p>The classic pathway is initiated by the binding of C1q, C1r and C1s (the C1 complex) to antibodies linked to the activation surface. The proteolytic activity of C1r is automatically activated by interaction with C1q. C1r then cleaves and activates C1s, which is another serine protease. C1s acts specifically on C2 and C4 activating them. Once cleaved, the fragment C4b is capable to bind covalently to the activation surface creating a binding site to C2a. The active serine protease C2a, in the C4b-C2a complex, acts on C3 producing C3b molecules which are also capable to bind covalently to the activation surface nearby its site of activation. The complex C4b-C2a-C3b acts as a C3 convertase as well as a C5 convertase generating the MAC. For activation of the alternative pathway, a small fraction of C3 present in the extracelular fluids slowly undergoes spontaneous reaction with H₂O molecules generating C3-H₂O. These molecules can interact with the protein B generating the B-C3-H₂O complex which is a substrate for D, a plasmatic serine protease. The Bb-C3-H₂O complex acts on C3 cleaving it to C3b and C3a. Most of the C3b molecules generated will combine with H₂O or other self molecules becoming inactive. On the other hand, if a C3b molecule is generated near an adequate surface such as a bacterium, it will covalently bind to it creating a binding site for factor B. The C3b-B complex is activated by the protease D generating C3b-Bb, an efficient protease capable to activate other C3 molecules. The complex C3b-Bb-C3b is an efficient C3 convertase as well as a C5 convertase generating the MAC. To simplify, the lectin pathway as well as the normal regulatory proteins were omitted.</p

Apyrase activity from the crop soluble contents of <i>Rhodnius prolixus</i> after artificial and forced feeding.

<p>The activity was expressed as ng of inorganic phosphate (Pi) released in a minute by 1/12 of anterior midgut contents±standard error. The T test indicated a significant difference between groups (P<0.05).</p

Protection of anterior midgut of <i>T. brasiliensis</i> against the complement system.

<p>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.</p

Influence of pH in the activation of complement system from different hosts.

<p>Activation of classical (A) and alternative (B) pathways from the serum of dogs, guinea pigs, rats and chickens at pH 7.4 and 8.15. </p

Kinetic lysis of <i>L. infantum</i> promastigotes by different concentrations of chicken sera in the presence and absence of <i>L. longipalpis</i> saliva.

<p>The results are expressed as the mean of the percentage of live cells ± SD. Three replicates were performed for each experiment.</p

Kinetic lysis of <i>L. infantum</i> promastigotes by chicken sera.

<p>Effect of different concentrations of chicken sera (<b>A</b>) and different incubation temperatures (<b>B</b>) on the viability of <i>L. Infantum</i> promastigotes. The results are expressed as the mean of the percentage of live cells ± SD. Three replicates were performed for each experiment. </p

Effect of <i>L. longipalpis</i> saliva on the C3b deposition of classical and alternative complement pathways of dogs and guinea pigs at pHs of 7.4 and 8.15.

<p>The guinea pig alternative pathway could not be assessed at a pH of 8.15 because the alkalinisation itself affects the pathway's efficiency in a way that the difference between the positive and negative controls is undetectable. The results are expressed as the mean of percentage of C3b deposition ± SD. Three replicates were performed per experiment.</p

Effect of <i>L. longipalpis</i> saliva on the classical pathway of the complement system from different hosts at pH 7.4 and pH 8.15.

<p>Effect of <i>L. longipalpis</i> saliva on the classical pathway of the complement system from different hosts at pH 7.4 and pH 8.15.</p