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

There is increasing evidence that compounds in tick saliva and salivary gla nd extract (SGE) have a suppressive effect on host immunity and that tick-b orne pathogens exploit this situation to their benefit thus causing disease s. We have demonstrated that SGE derived from Rhipicephalus appendiculatus ticks has a suppressive effect on a macrophage like cell line, JA-4, in ter ms of secretion as well as mRNA transcription of three cytokines. Percent s uppression of cytokine secretion by JA-4 cells cultured in the presence of lipopolysaccharide (LPS) and SGE in comparison to JA-4 cells cultured in th e presence of LPS alone was 67.8, 89.1 and 82.0% for IL-1 alpha, TNF-alpha and IL- 10, respectively (P < 0.05) A similar pattern of results was demons trated in terms of mRNA transcription where SGE-induced suppression was 36. 9% for IL-1 alpha, 25.0% for TNF-alpha and 31.5% for IL-10 (P < 0.05). In a ddition, we have demonstrated that SGE partially inhibited nitric oxide pro duction by JA-4 activated with LPS. The results of the present study sugges t that tick salivary gland compounds may exert their effect in vivo by bloc king the functions of macrophages in the transcription of cytokines and pro duction of nitric oxide. This SGE-induced immunomodulation may comprise a m ajor gateway in the facilitation of tick feeding and transmission of pathog ens in hosts. (C) 2001 Elsevier Science B.V. All rights reserved.