The Effects of 20-Hydroxyecdysone and Juvenile Hormone III on Tick Cells

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Abstract
Two cell lines isolated from Rhipicephalus appendiculatus (RAE 25) and Anocentor (= Dermacentor) nitens (ANE 58) responded to the invertebrate hormones 20-hydroxyecdysone (20-HE) and juvenile hormone III (JH III) in vitro. In the presence of 0.2 or 2 nM 20-HE the cells of the continuous line RAE 25 attached to the culture substrate at a rate of 9%/h for the 1st 8 h, as did cells in growth medium. High concentration, 20 or 200 nM of 20-HE, reduced the rate of cell attachment to 6%/h, and in the higher hormone concentration the cells ceased to attach after 4 h. Low concentrations (0.2 and 2 nM) of 20-HE stimulated the growth of the RAE 25 line (P < 0.02), but 200 nM or more inhibited growth (P < 0.001). Twenty-HE suppressed the growth of the young line ANE 58 in a dose-dependent manner, but the decrease in cell growth was less pronounced than in RAE 25. Ten to 100 times more (2 and 20 .mu.M) 20-HE was needed to achieve significant growth suppression (P < 0.025 and < 0.005). The growth of both lines declined (P < 0.01) by 20% (RAE 25) or 30% (ANE 58) when the medium contained 38 .mu.M of JH III. The bimodal growth response of line RAE 25 to 20-HE also occurred in the presence of 3.8 and 38 .mu.M JH III, and 2 nM 20-HE counteracted the suppressive effect of 38 .mu.M JH III. Under the influence of 20-HE, the epithelial-like RAE 25 cells aggregated, detached and formed vesicles after certain times, depending on hormone concentration: 5-6 days with 2 nM, 2 days with 20 nM, and 1 day with 200 nM or more. The hemocytelike cells of ANE 58 were less sensitive to 20-HE. In the presence of 2-20 .mu.M 20-HE, the pseudopodia retracted and 70% of the cell population detached. The responses of acarine cells to the hormones 20-HE and JH III are contrasted with those reported for insect cells in culture.

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