MODULATION OF MURINE IMMUNOLOGICAL RESPONSES BY SALIVARY-GLAND EXTRACT OF SIMULIUM-VITTATUM (DIPTERA, SIMULIIDAE)

The influence of Simulium vittatum Zetterstedt salivary gland extract on several immunological mechanisms was investigated in murine model h osts (laboratory mice). These mechanisms included the expression of ma jor histocompatibility complex class II cell surface molecules, the in vitro mitogen responsiveness of lymphoid cells, and the antibody resp onses to heterologous foreign antigens (sheep erythrocytes). Experimen ts were designed to determine the influence of salivary gland extract following in vivo inoculation or in vitro inclusion in cell culture. I n vivo inoculation of salivary gland extract reduced the percentage of Ia+ cells in spleen cell populations, although this difference was am eliorated by a 2 d in vitro culture per-iod, regardless of whether sal ivary gland extract was included in culture. Salivary gland extract ha d no effect on Ia expression by cells derived from regional lymph node s or the skin (epidermis). In vivo inoculation with salivary gland ext ract did not affect the responsiveness of splenic lymphocytes to mitog ens, whereas in vitro exposure to salivary gland extract reduced both T and B cell mitogenesis. Finally, antibody responses to sheep erythro cytes were enhanced if salivary gland extract was included as a coinoc ulant, although this was expressed only at the systemic level regardle ss of the route of antigen delivery. In light of these results, immuno modulatory functions of black fly saliva are postulated; they are oper ative at different levels on different subcompartments of the immune s ystem, possibly via cytokine modulation.