MODULATION OF MURINE CELLULAR IMMUNE-RESPONSES AND CYTOKINES BY SALIVARY-GLAND EXTRACT OF THE BLACK FLY SIMULIUM-VITTATUM

Salivary gland extract (SGE) of the blood-feeding black fly Simulium vittatum is known to modulate immunological responses. In the present study, the ability of S. vittatum SGE to modulate responses during heterologous antigenic challenge was investigated in a murine model, with particular emphasis on characterizing the patterns of cytokine response. Mice were injected repeatedly with SGE or saline (sham), then challenged with the T dependent antigen ovalbumin (OVA) to generate antigen-specific lymphoblasts. Spleen cells from OVA-primed mice were then co-cultured with OVA in vitro to stimulate cytokine secretion. Cells from mice that had been injected with SGE prior to OVA challenge produced lower levels of interleukins 5 and 10 (IL-5 and IL-10) in in vitro culture, when stimulated with OVA, compared to mice that had been sham-injected with saline. Levels of IFN-gamma IL-2 and IL-4 did not differ significantly between SGE- and saline-injected groups. Mice injected repeatedly with SGE prior to OVA challenge had fewer circulating eosinophils than sham-injected mice, while other leukocyte levels were unaffected by SGE. Prior exposure to SGE did not affect levels of serum IgE or IgA significantly. The effect of SGE on the ability of murine spleen cells to respond in vitro to the recombinant cytokines IL-2 and IL-4 was also investigated. Naive spleen cells pre-incubated with SGE proliferated less in response to both IL-2 and IL-4 in in vitro culture than cells pre-incubated with saline as a control. Residual levels of IL-4 were higher in culture supernatants of SGE-treated cells following cytokine stimulation, suggesting that SGE had inhibited the cells' ability to utilize exogenous IL-4. This report emphasizes that immunological studies of vector-borne diseases should not overlook the important contribution of the vector to host immunocompetence. Results are discussed with particular emphasis on the use of murine models in studies of onchocerciasis.