Salivary gland extract of Rhipicephalus appendiculatus ticks inhibits in vitro transcription and secretion of cytokines and production of nitric oxide by LPS-stimulated JA-4 cells

Abstract

There is increasing evidence that compounds in tick saliva and salivary gland extract (SGE) have a suppressive effect on host immunity and that tick-borne pathogens exploit this situation to their benefit thus causing diseases. We have demonstrated that SGE derived from Rhipicephalus appendiculatus ticks has a suppressive effect on a macrophage like cell line, JA-4, in terms of secretion as well as mRNA transcription of three cytokines. Percent suppression of cytokine secretion by JA-4 cells cultured in the presence of lipopolysaccharide (LPS) and SGE in comparison to JA-4 cells cultured in the presence of LPS alone was 67.8, 89.1 and 82.0% for IL-1α, TNF-α and IL-10, respectively ( P<0.05). A similar pattern of results was demonstrated in terms of mRNA transcription where SGE-induced suppression was 36.9% for IL-1α, 25.0% for TNF-α and 31.5% for IL-10 ( P<0.05). In addition, we have demonstrated that SGE partially inhibited nitric oxide production by JA-4 activated with LPS. The results of the present study suggest that tick salivary gland compounds may exert their effect in vivo by blocking the functions of macrophages in the transcription of cytokines and production of nitric oxide. This SGE-induced immunomodulation may comprise a major gateway in the facilitation of tick feeding and transmission of pathogens in hosts.