The role of saliva of Anopheles stephensi in inflammatory response: identification of a high molecular weight neutrophil chemotactic factor

Abstract

Mosquito bites can elicit dermal hypersensitivity reactions, but little is known about the chemotactic factors for host leukocytes in mosquito saliva. In this study, we determined that saliva from a malarial vector mosquito, Anopheles stephensi, possesses intense neutrophil chemotactic activity. In contrast, the midgut extract had only marginal neutrophil chemotactic activity. Eosinophil chemotactic activity was detected in the midgut but not in the saliva. According to the results of size-exclusion HPLC on a G3000SW column and Western blot analysis, the apparent molecular weight (MW) of the main neutrophil chemotactic factor (NCF) was estimated to be 200 kDa. NCF could bind with IgG from the pooled serum of Solomon islanders, whereas not with that of healthy Japanese. NCF activity was increased upon heating to 56 degrees C for 30 min or protease digestion, whereas it was affected by periodate treatment. Protease-digested NCF and naive NCF bound to lentil lectin-Sepharose, and both were eluted with a competitive sugar, methyl-alpha-D-glucoside. These results indicate that A. stephensi saliva-derived NCF is a high MW glycoprotein, and its protein moiety is important for neutrophil chemotactic activity. This NCF is thought to contribute to the inflammatory reactions through the accumulation of neutrophils at the site of the mosquito bite.

Anopheles Mosquito Bites Activate Cutaneous Mast Cells Leading to a Local Inflammatory Response and Lymph Node Hyperplasia

“…A high m.w. glycoprotein from A. stephensi saliva endowed with a direct neutrophil chemotactic activity has been observed in vitro (43). Possibly due to differences in terms of dose and freshness of saliva mediators, our work in vivo does not support these observations because mosquito bites failed to induce neutrophil infiltration in mast cell-deficient mice and rather emphasizes a critical role of mast cells in the accumulation of neutrophils at the site of mosquito bite.…”

Members of the Salivary Gland Surface Protein (SGS) Family Are Major Immunogenic Components of Mosquito Saliva

“…There is now a strong body of evidence supporting an immunomodulatory effect by mosquito saliva, although the identity of these immunomodulatory proteins has not been determined (10). One such factor is a large immunogenic protein from Anopheles stephensi that possesses neutrophil chemotactic activity (9). Another large immunomodulatory protein was discovered from A. aegypti saliva, is about 387 kDa, and significantly lowers cytokine release and the proliferation of murine T-and B-cells (20).…”

“…A candidate is gSG6, a protein found only in mosquitoes of the genus Anopheles that has shown promise in several laboratory and field studies (6,7). The identification of other mosquito-specific (and genus-specific) salivary immunogens should improve this epidemiological method, and published data suggest that there are other yet unidentified saliva proteins that are more immunogenic than gSG6 (8,9).…”

Mast Cell-Dependent Down-Regulation of Antigen-Specific Immune Responses by Mosquito Bites

“…Recently, saliva from Anopheles stephensi has been shown to contain a high m.w. glycoprotein endowed with an intense neutrophil chemotactic activity which contributes to the inflammatory reaction through the accumulation of neutrophils at the site of the mosquito bite (5). Mosquito bites can elicit both immediate (6) as well as delayed hypersensitivity reactions (7).…”