Research brief Schistosoma mansoni: Melatonin enhances efficacy of cercarial and soluble worm antigens in the induction of protective immunity against infection in the hamster Maha F.M. Soliman * , Nahla S. El Shenawy, Shimaa E. El Arabi Zoology Department, Faculty of Sciences, Suez Canal University, El Da aeri kilo4, Ismailia, Egypt Received 13 September 2007; received in revised form 25 January 2008; accepted 29 January 2008 Available online 6 February 2008 Abstract Based on the beneficial influence of melatonin administration on the course of schistosomiasis and on its possible action on the immune system, we aimed in this study to establish an immunization program using Schistosoma mansoni adult worm antigen (SWAP) and cercarial antigen (CAP) alone or concurrently with melatonin treatment, for 30 successive days, in an attempt to enhance their effi- cacy against the infection in hamsters. Results showed that the worm reduction percentages were 53.8%, 67.01%, 56.4% and 99.3% for CAP, CAP + melatonin, SWAP, SWAP + melatonin, respectively, indicating that melatonin enhanced efficacy of SWAP but only pro- duced a slight increase in efficacy of CAP. Highly significant reductions in egg load in the liver and alteration in the oogram pattern with a high percentage of immature eggs and few dead eggs were recorded in the groups that received melatonin treatment suggesting a pos- sible role for melatonin in the regulation of egg production and development. On the other hand, melatonin clearly improved the oxi- dative status in the immunized groups. No antibody (Ab) response was recorded in the groups immunized with SWAP + melatonin while low Ab level was seen in the other melatonin-treated group. In addition to the antioxidant properties of melatonin, our results suggested that the early and continuous melatonin administration may result in immunomodulatory actions which in turn enhanced the efficacy of SWAP and CAP in different ways. This indicates the importance of further investigation of the mechanisms of melatonin action and the possible application in a vaccination program. Ó 2008 Elsevier Inc. All rights reserved. Index Descriptors and Abbreviations: Schistosomiasis; Immunization; Antigens; Melatonin 1. Introduction Despite three decades of widespread, safe and effective chemotherapy (praziquantel), the number of people with schistosomiasis worldwide remains at about 200 million (Wilson and Coulson, 2006). The good safety, and broad therapeutic profile of praziquantel and the sharp reduction in its price have stalled the improvement and advancement of other potential control options for schistosomiasis, such as vaccines (Utzinger et al., 2007) or new tools for treat- ment (Soliman and Ibrahim, 2005). Evidence of praziquan- tel resistance and the high rates of re-infection which demand repeated treatment, have highlighted the need for vaccines that provide long term immunity. Consequently, an effective schistosome vaccine is a desirable control tool but progress towards that goal has been slow (Wilson and Coulson, 2006; Uribe et al., 2007). Different Schistosoma mansoni antigens including adult worm antigen (SWAP), cercarial antigen (CAP), egg anti- gen (EAP) and lung-stage antigen (SLAP) have been used to immunize experimental animals against S. mansoni either alone, in combination or with adjuvants (Blanton et al., 1991; Tendler et al., 1991; Bahia-Oliveira et al., 1992; El Ridi et al., 1993; Akhiani et al., 1997; Ashour et al., 2004; Afifi et al., 2006). Unfortunately, these studies 0014-4894/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.exppara.2008.01.013 * Corresponding author. E-mail address: maha_soliman@hotmail.com (M.F.M. Soliman). www.elsevier.com/locate/yexpr Available online at www.sciencedirect.com Experimental Parasitology 119 (2008) 291–295