Human immune response to salivary proteins of wild-caught Phlebotomus papatasi

Abstract

Phlebotomine sand flies are the known vectors of Leishmania parasites. New approaches in vaccination against Leishmania have investigated the possibility of integrating Phlebotomus papatasi salivary proteins to enhance the immune response and protect against the transmission of the infection. The aim of the present study was to screen human immune responses to wild sand fly saliva and evaluate immunogenic salivary proteins. Blood samples were collected from donors in control and sand fly infested areas. Antibodies specific for sand fly antigens in donor plasma were probed using immunoblotting. In addition, recall proliferation capability of peripheral blood mononuclear cells (PBMC) was tested after sand fly salivary homogenates stimulation. The significant immunogenic salivary proteins (SPs) identified by immunoblotting were SP28, SP32, and SP36. A specific proliferative response of PBMC after stimulation with sand fly salivary homogenates was evident in donors that have antibody responses against sand fly salivary proteins. Individuals with antibody recognition to a higher number of salivary proteins (i.e., 3 or more SP bands) showed lower PBMC proliferative responses after in vitro stimulation with salivary gland homogenates (SGH) only in the sand fly infested, leishmaniasis free area. Interestingly, the presence of a humoral immune response to many SP antigens inversely correlates with a strong cell-mediated immune response (CMI). It was also noticed that some other heavily expressed antigens, in sand fly salivary homogenate, lack or have weak humoral immune reactivity in exposed individuals. Therefore, considering these antigens alone as CMI activators, without including the immunodominant humoral immune response proteins, needs future investigation.

Keywords: Leishmania; Leishmania major; Phlebotomus papatasi; Proliferation; Salivary proteins; Sand fly.