Schistosoma mansoni: pH dependence of cercarial eicosanoid production, penetration, and transformation

Abstract

The pH dependence of Schistosoma mansoni cercarial penetration and transformation was determined using a gelatin:agar matrix, containing 3m M linoleate, as a penetration substrate. Penetration was largely unaffected by pH, approaching 100% over the pH range of 5.4 to 8.2, while transformation had an optimum pH range between 6.2 and 7.4. Within this pH range, between 74 and 89% of cercariae lost their tails. Outside this range, transformation decreased to 0% above pH 7.8 and dropped to 57% at pH 5.4. Esculetin, a lipoxygenase inhibitor, also incorporated into the agangelatin plates at a concentration of 1 m M, had little effect on cercarial penetration, except between pH 6.5 and 6.65, where penetration rates fell to 50% at pH 6.63. Transformation, however, was inhibited by esculetin, except between pH 6.5 and 6.8, where transformation was statistically equivalent to controls ( P = 0.064, two-tailed Student's t test). Cercarial eicosanoid production measured at pH 6.55 and 7.2 in the presence and absence of 1 m M esculetin has led to the tentative identification of a 5-lipoxygenase product associated with cercarial penetration: LTB 4 or 6-trans LTB 4, a breakdown product of LTB 4. We discuss the importance of pH control in cercarial experiments as well as the possible modulatory role skin pH (surface, epidermal, and dermal) may have in regulating cercarial eicosanoid production.