Differential modulation of murine cellular immune responses by salivary gland extract of Aedes aegypti.

The ability of salivary gland extract (SGE) of Aedes aegypti to modulate cellular immune responses was investigated in a mouse model. Cytokine production was induced in naive and antigen-primed murine (BALB/c) spleen cells in vitro by stimulation with the T cell mitogen concanavalin A or the T cell-dependent antigen ovalbumin (OVA), respectively. Inclusion of Ae. aegypti SGE in in vitro culture with naive cells caused significant suppression of the cytokines interleukin-2 (IL-2) and interferon gamma in culture supernatants, while levels of other cytokines (IL-4 and IL-5) were unaffected by SGE. In contrast, SGE did not affect cytokine production by antigen-activated cells derived from OVA-primed mice. To determine whether SGE could inhibit the responsiveness of cells to exogenous cytokine stimuli, optimized quantities of lymphocyte growth factor cytokines IL-2 and IL-4 were added to SGE-treated spleen cells and the degree of cellular proliferation was determined. Cellular proliferation in response to IL-2 was markedly suppressed by prior exposure of cells to SGE, while the proliferative response to IL-4 was also affected by SGE but to a lesser extent. These results confirm that mosquito SGE can modulate host immune responses, and suggest that in Ae. aegypti modulation is directed primarily against cytokines associated with type 1 lymphocyte responses. The mode of immunomodulation and the possible relevance of these results to vector-borne disease research are discussed.