Natural human humoral response to salivary gland proteins of Anopheles mosquitoes in Thailand

During blood feeding, arthropod vectors inject saliva into vertebrate hosts. The saliva is biochemically complex and pharmacologically active, and may play an important role in pathogen transmission. To examine whether mosquito saliva could elicit humoral immune response in humans under natural conditions, we have collected sera from malaria patients, healthy villagers, and people from a non-malarious region in Thailand. Here we have demonstrated that anti-Anopheles salivary protein antibodies occurred predominantly in patients with acute Plasmodium falciparum or P. vivax malaria, whereas people from a non-malarious area had no such antibodies. Besides, antibody levels against mosquito salivary proteins in malaria patients were highly variable, which may be related to the levels of mosquito exposure. Despite variability, patients’ sera with high IgG titers consistently detected several proteins in Anopheles dirus salivary gland protein extracts. Immunohistochemical staining of Anopheles salivary glands with human sera showed that the salivary gland-specific IgGs reacted strongly with the median lobe. Comparison using Anopheles and Aedes salivary proteins suggests that the anti-salivary protein antibodies detected in malaria patients were Anopheles-specific, consistent with the major malaria vector status of An. dirus in this area.