Effects of Dermacentor andersoni (Acari: Ixodidae) salivary gland extracts on Bos indicus and B. taurus lymphocytes and macrophages: in vitro cytokine elaboration and lymphocyte blastogenesis.

Cattle and laboratory animal species-acquired resistance to tick infestation has an immunological basis involving antigen presenting cells, B-lymphocytes, T-lymphocytes, and cytokines. Tick infestation has been shown to impair guinea pig antibody responses to a thymic-dependent antigen and in vitro responsiveness of lymphocytes to T-cell mitogens. Tick salivary gland extracts inhibited in vitro proliferative responses of normal murine lymphocytes to the T-cell mitogen concanavalin A (Con A) and enhanced reactivity of normal B-lymphocytes to the mitogen E. coli lipopolysaccharide (LPS). Salivary gland extracts collected daily during engorgement were shown to inhibit normal murine macrophage elaboration of interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF) as well as murine T-lymphocyte production of interleukin-2 (IL-2) and interferon-gamma (IFN-G). Peripheral blood mononuclear cells collected from purebred Bos indicus and B. taurus were significantly inhibited in their in vitro responses to Con A by salivary gland extracts prepared daily from female Dermacentor andersoni stiles during the course of engorgement. Percentage of suppression of Con A responsiveness was similar for both B. indicus and B. taurus cells. The overall responsiveness of B. indicus derived T cells is significantly greater than that of similar cells from B. taurus, when mean counts per minute of methyl-tritiated-thymidine incorporation were compared for both groups. Cells of B. indicus origin were 34.5% more reactive. In vitro responsiveness of the same cell populations to LPS were significantly enhanced by the presence of tick salivary gland extracts. B. indicus lymphocyte reactivity to LPS was significantly greater (42.9%) than that of similar B. taurus cells in the absence of salivary gland extracts. B. indicus and B. taurus macrophage elaboration of IL-1 were suppressed in a similar manner by tick salivary gland extracts prepared on days 5-9 of engorgement. B. indicus macrophages produced more IL-1 than similar cells of B. taurus origin either in the presence (45.6%) or absence (43.0%) of LPS. Macrophages derived from both genetic backgrounds were significantly suppressed in their LPS induced production of TNF in the presence of tick salivary gland extracts collected on days 0-9 of engorgement. B. indicus might be able to develop more vigorous immune responses to foreign immunogens presented to the animal during tick feeding.