Saliva of the Yellow Fever mosquito, Aedes aegypti, modulates murine lymphocyte function

Abstract

Saliva of many vector arthropods contains factors that inhibit haemostatic responses in their vertebrate hosts. Less is known about the effect of vector saliva on host immune responses. We investigated the effect of Aedes aegypti salivary gland extracts on antigen-stimulated responses of transgenic OVA-TCR DO11 mouse splenocytes in vitro. T-cell proliferation was inhibited in a dose-dependent manner, with greater than 50% inhibition at 0.3 salivary gland pair (SGP) equivalents/mL. LPS-stimulated B-cell proliferation was also inhibited. Secretion of the Th1 cytokines IL-2 and IFN-gamma was reduced by 50% or more with 0.45-0.6 SGP/mL, as was secretion of the pro-inflammatory cytokines GM-CSF and TNF-alpha, and the Th2 cytokine IL-5. The Th2 cytokines IL-4 and IL-10 were similarly reduced with 0.6-2 SGP/mL. Inhibition of lymphocyte function involved modulation of viable T-cells at low salivary gland extract (SGE) concentrations, and decreased viability at higher concentrations. Dendritic cells were not killed by salivary gland extracts at concentrations as high as 25 salivary gland pairs/mL, but secretion of IL-12 was inhibited by 87% following exposure to 0.6 SGP/mL. Activity is present in saliva and extracts of female but not male salivary glands, and it is depleted from salivary glands of blood-fed mosquitoes. The activity is denatured by boiling and by digestion with the protease papain, indicating a protein; gel filtration HPLC indicates a mass of about 387 kDa. These results suggest that A. aegypti saliva exerts a marked immunomodulatory influence on the environment at the bite site.

The enhancement of arbovirus transmission and disease by mosquito saliva is associated with modulation of the host immune response

“…This pattern suggests that at the immediate feeding site, an immunosuppressed environment is created, whereas more distal regions with decreasing saliva concentrations experience a dysregulation of the immune response. A 387 kDa protein was implicated in this observed activity (Wasserman et al 2004). Depinay et al (2006) observed a suppression of antibody-specific T cell responses mediated by Anopheles stephensi saliva and dependent on mast cells and IL-10 expression.…”

“…It is now clear that the feeding of mosquitoes has an immunomodulatory effect on their hosts (Billingsley et al 2006, Cross et al 1994, Depinay et al 2006, Wanasen et al 2004, Wasserman et al 2004, Zeidner et al 1999. The presence of this activity in vector saliva is a reflection of the inherent overlapping and interconnected nature of the host haemostatic and inflammatory/immunological responses and the intrinsic need to prevent these host defences from disrupting successful feeding.…”

“…pipiens, an ornithophilic species (Wang 1975), has less immunomodulatory effect on mammals (Wanasen et al 2004). Parallel work by Wasserman et al (2004) demonstrated that T-and B-cell proliferation was inhibited in a dose dependent manner from concentrations as low as 0.15 salivary gland pairs (SGP)/ml. Each mosquito possesses a pair of salivary glands, and it has been estimated that mosquitoes inject about 50-60% of their active salivary factors during a feed and re-ingest approximately 20%, leaving roughly 30-40%, or the equivalent of 0.3-0.4 SGP, in the skin (Wasserman et al 2004).…”

“…Parallel work by Wasserman et al (2004) demonstrated that T-and B-cell proliferation was inhibited in a dose dependent manner from concentrations as low as 0.15 salivary gland pairs (SGP)/ml. Each mosquito possesses a pair of salivary glands, and it has been estimated that mosquitoes inject about 50-60% of their active salivary factors during a feed and re-ingest approximately 20%, leaving roughly 30-40%, or the equivalent of 0.3-0.4 SGP, in the skin (Wasserman et al 2004). Lower concentrations of SGE inhibited T H 1 cytokines (IL-2 and IFN-γ) and T cell proliferation, while higher concentrations suppressed T H 1, T H 2 (IL-4 and IL-10), and proinflammatory (granulocyte macrophage colony stimulating factor and TNF-α) cytokines and decreased T cell viability.…”

“…Mosquitoes, like all haematophagous arthropods, have evolved mechanisms to effectively neutralize host haemostatic responses, based upon the release of saliva into the feeding site. Saliva is a pharmacologic cocktail of secreted molecules, principally proteins, that can affect vascular constriction, blood coagulation, platelet aggregation, inflammation, immunity, and angiogenesis (Arca et al 1999, Arca et al 2002, Arca et al 2005, Billingsley et al 2006, Calvo et al 2004, Calvo et al 2006a, Calvo et al 2006b, Calvo and Ribeiro 2006, Champagne 2004, Champagne et al 1995, Cross et al 1994, James et al 1991, Kerlin and Hughes 1992, Mellink and Vos 1977, Ribeiro 1987, 1989b, 1992, Ribeiro et al 2000, Ribeiro and Francischetti 2001, 2003, Ribeiro and Nussenzveig 1993, Ribeiro et al 1994, Stark and James 1998, Suwan et al 2002, Valenzuela et al 2002, Wanasen et al 2004, Wasserman et al 2004, Zeidner et al 1999. The saliva of all species of haematophagous arthropod analyzed to date contains at least one anticlotting, one anti-platelet, and one vasodilatory substance.…”