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 v ittatum is known to modulate immunological responses. In the present s tudy, the ability of S. vittatum SGE to modulate responses during hete rologous antigenic challenge was investigated in a murine model, with particular emphasis on characterizing the patterns of cytokine respons e. Mice were injected repeatedly with SGE or saline (sham), then chall enged 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 fro m 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 cu lture, when stimulated with OVA, compared to mice that had been sham-i njected with saline. Levels of IFN-gamma IL-2 and IL-4 did not differ significantly between SGE- and saline-injected groups. Mice injected r epeatedly with SGE prior to OVA challenge had fewer circulating eosino phils than sham-injected mice, while other leukocyte levels were unaff ected 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 sple en cells to respond in vitro to the recombinant cytokines IL-2 and IL- 4 was also investigated. Naive spleen cells pre-incubated with SGE pro liferated less in response to both IL-2 and IL-4 in in vitro culture t han cells pre-incubated with saline as a control. Residual levels of I L-4 were higher in culture supernatants of SGE-treated cells following cytokine stimulation, suggesting that SGE had inhibited the cells' ab ility to utilize exogenous IL-4. This report emphasizes that immunolog ical studies of vector-borne diseases should not overlook the importan t contribution of the vector to host immunocompetence. Results are dis cussed with particular emphasis on the use of murine models in studies of onchocerciasis.