Immunological mechanisms involved in macrophage activation and polarization in schistosomiasis

Human schistosomiasis is caused by helminths of the genus Schistosoma. Macrophages play a crucial role in the immune regulation of this disease. These cells acquire different phenotypes depending on the type of stimulus they receive. M1 macrophages can be ‘classically activated’ and can display a proinflammatory phenotype. M2 or ‘alternatively activated’ macrophages are considered anti-inflammatory cells. Despite the relevance of macrophages in controlling infections, the role of the functional types of these cells in schistosomiasis is unclear. This review highlights different molecules and/or macrophage activation and polarization pathways during Schistosoma mansoni and Schistosoma japonicum infection. This review is based on original and review articles obtained through searches in major databases, including Scopus, Google Scholar, ACS, PubMed, Wiley, Scielo, Web of Science, LILACS and ScienceDirect. Our findings emphasize the importance of S. mansoni and S. japonicum antigens in macrophage polarization, as they exert immunomodulatory effects in different stages of the disease and are therefore important as therapeutic targets for schistosomiasis and in vaccine development. A combination of different antigens can provide greater protection, as it possibly stimulates an adequate immune response for an M1 or M2 profile and leads to host resistance; however, this warrants in vitro and in vivo studies.

Praziquantel: An update on the mechanism of its action against schistosomiasis and new therapeutic perspectives

Praziquantel (PZQ) is the drug of choice for the treatment of all forms of schistosomiasis, although its mechanisms of action are not completely understood. PZQ acts largely on adult worms. This narrative literature review describes what is known about the mechanisms of action of PZQ against schistosomes from in vitro and in vivo studies and highlights the molecular targets in parasites and immune responses induced in definitive hosts by this drug. Moreover, new therapeutic uses of PZQ are discussed. Studies have demonstrated that in addition to impacting voltage-operated Ca2 + channels, PZQ may interact with other schistosome molecules, such as myosin regulatory light chain, glutathione S-transferase, and transient receptor potential channels. Following PZQ administration, increased T regulatory type 1 (Tr1) cell differentiation and decreased inflammation were observed, indicating that PZQ promotes immunoregulatory pathways. Although PZQ is widely used in mass drug administration schemes, the existence of resistant parasites has not been proven; however, it is a concern that should be constantly investigated in human populations. In addition, we discuss studies that evaluate health applications of PZQ (other than helminth infection), such as its effect in cancer therapy and its adjuvant action in vaccines against viruses.

Molluscicidal activity of monoterpenes and their effects on inhibition of acetylcholinesterase activity on Biomphalaria glabrata, an intermediate host of Schistosoma mansoni

The molluscicidal action of essential oils have been attributed to the most prevalent terpene compounds. However, molluscicidal properties, mode of action, and toxicity to non-target organisms remain unclear. In this study, the molluscicidal potential of four monoterpenes (camphor, thymol, α-pinene, and 1,8-cineole) against the snail Biomphalaria glabrata, an intermediate host of Schistosoma mansoni, was analyzed. The molluscicide activity of each monoterpene was assessed by the standardized test of the World Health Organization (WHO) and the monoterpenes considered active against B. glabrata were analyzed as inhibitors of the enzymatic activity of acetylcholinesterase (AChE) extracted from snails. In addition, acute toxicity to non-target organisms was assessed against Danio rerio fish. The results show that camphor and 1,8-cineole monoterpenes did not induce snail mortality. Thymol and α-pinene were active against B. glabrata, inducing mortality in concentration-dependent patterns and showing a lethal effect in concentrations compatible with that recommended by the WHO (LC₉₀ of 7.11 and LC₉₀ 10.34 μg ∙ mL^-1, respectively). The toxic action of thymol and α-pinene on snails indicates that these monoterpenes may account for or largely contribute to the molluscicidal activity of essential oils that contain them as major compounds. Thymol and α-pinene inhibit the AChE of B. glabrata at concentrations higher than those used in the molluscicide test. These monoterpenes show low toxicity to non-target organisms compared to the commercial molluscicide niclosamide. Knowledge about monoterpene toxicity against B. glabrata contributes to its potential use in molluscicidal formulations and in alternatives to the control of snails that host intermediate S. mansoni, a crucial action in the prevention and transmission of schistosomiasis, a neglected tropical disease.