The sustainable role of parasites in modulating environment, immune system and gut microbiota

Abstract

Parasites are known as detrimental organism due to their adverse effects on human and animal health. However, besides negative effects, they play critical roles in various ecological and physiological processes. For example, they serve as bio accumulators that help control pollution. Cestodes such as Paraotigmatobothrium and Anthrobothrium species carry high levels of lead and cadmium than the tissues of their host fish. Recent researches have revealed that parasites present in fish species like Oreochromis niloticus, Parachanna obscura, and Clarias gariepinus are capable of accumulating higher levels of heavy metals which affects the overall burden in aquatic system. On the other hand, parasites plays significant role in the modulation of immune system by various pathways. Anti-inflammatory protein-2 (AIP-2) is a hookworm protein which is responsible for expansion of regulatory T cells (Tregs), resulting in reduction of inflammation in animal models of colitis. Similarly, Transforming Growth Factor-β mimic (TGM) obtained from Heligmosomoides polygyrus Tregs by binding with TGF-β receptors (TGFβR). Both TGFβR-I and TGFβR-II receptor chains can independently and firmly bind to TGM. But TGF-β directly binds with TGFβR-II chain, which then phosphorylates TGFβR-I. Another example is P53, a Trichuris muris derived protein, which plays a significant role in suppression of type 2 immune responses by trapping interleukin-13 (IL-13) in extracellular matrix. This trapping of cytokine is facilitated by thrombospondin-like binding motif present in p53. Helminths play a significant therapeutic role in autoimmune disorders, such as alleviation of multiple sclerosis and ulcerative colitis by regulating immune responses. A study in Argentina revealed that gastrointestinal helminth infection causes high levels of IL-10 and TGF-β resulting suppression of multiple sclerosis. Similarly, experimental infection with Trichuris trichiura has alleviated the symptoms of ulcerative colitis. Parasites also have the potential to alter the host gut physiology and microbial dynamics. The physiological processes like cell proliferation, apoptosis, and cell activity are influenced by the presence of Trichuris in large intestine. Furthermore, certain species of protozoa have significant effect on gut health and microbial balance by altering the Firmicutes-to-Bacteriodetes ratio. Parasites are necessary for one health by playing crucial role in supporting environment and animal and human health, yet in moderate concentration.