Summary

Parasitic helminths (metazoa) and protozoa are vastly diverse groups of eukaryotic organisms that cause various diseases in humans and animals. The complex interactions between hosts and parasites remain a puzzling question. Control of parasitic infections requires an efficient immune response that must be balanced against destructive pathological consequences. Parasites elicit humoral and cellular immune responses in infected hosts. However, immunological protection against parasitic infections is much less efficient than that against bacteria or viruses. The complex antigenic and structural nature of parasites impedes the immune response from being directed against a specific antigen. Besides, most parasitic infections are chronic and show a degree of host specificity. This entry collection aims to unravel the panoply of the less-explored activities of nitric oxide (NO) and neutrophil extracellular traps (NETs) against different parasitic elements.

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Topic Review
Nitric Oxide Synthase in Experimental Chronic Toxoplasmosis
The coccidian protozoan Toxoplasma gondii (T. gondii) is among the most prevalent zoonotic parasites worldwide. Nitric oxide (NO) production by macrophages is considered a critical microbicidal mechanism against various intracellular pathogens, including T. gondii. While the role of the inducible nitric oxide synthase isoenzyme (iNOS) has been widely investigated in both acute and chronic T. gondii infections, the specific functions of the neuronal (nNOS) isotype in the antiparasitic immune response, particularly during chronic toxoplasmosis, remain largely uncovered. Hence, this report seeks to bridge the gap regarding the potential participation of nNOS in experimental chronic T. gondii infection. Methods: The study included 56 Swiss albino mice, equally allocated into four experimental groups: (G1) negative control, (G2) infected control, (G3) infected-L-arginine-treated, and (G4) infected-7-Nitroindazole-treated. All groups except (G1) were orally infected with the avirulent (ME49) T. gondii strain. Nine weeks post-infection, all mice were euthanized for parasitological, histopathological, immunohistochemical, and biochemical analyses. Results: The NO donor, L-arginine, induced a significant reduction in the number of T. gondii cysts, together with strong nNOS immunoreactivity in the brain sections of the treated mice. Conversely, the highest parasitic burden was observed following selective nNOS inhibition with 7-Nitroindazole, exacerbating parasite-induced pathology. Conclusions: The neuronal isotype serves as a critical source of NO production during the chronic stage of T. gondii infection, thereby enhancing parasite elimination and contributing to host tissue protection.
  • 55
  • 03 Nov 2026
Topic Review
The Dichotomous Nature of Nitric Oxide in Trichinosis
The exact role of nitric oxide (NO) in the complex interplay between the host and Trichinella spiralis (T. spiralis) parasite remains uncovered. While much has been revealed about the role of the inducible isoenzyme (iNOS) in different parasitic infections, research is slowly progressing toward understanding the neuronal enzyme (nNOS)-derived impacts on trichinosis. This study aims to clarify the dual nature of (NO) during the enteral phase of experimental trichinosis by examining the participation of both iNOS and nNOS in T. spiralis-infected mice. The experimental design included 48 male Swiss albino mice divided into six groups: (G1) negative control, (G2) infected control, (G3) infected–Albendazole-treated, (G4) infected-infected–L-arginine-treated, (G5) infected–Aminoguanidine-treated, and (G6) infected–7-Nitroindazole-treated. On the seventh day post-infection, the study groups underwent parasitological (adult worm count), histopathological, immunohistochemical, and biochemical assessments. Our results showed that (nNOS) predominance during the enteral phase of trichinosis enhanced parasitic clearance. Conversely, NO produced by iNOS was not essential for worm expulsion but contributed to T. spiralis-mediated enteropathy. Nitric oxide seems to play a puzzling role in T. spiralis infection. While (iNOS) is known for eliminating numerous infections, this is the first example we are aware of where the activity of the neuronal isoform (nNOS) is required in trichinosis.
  • 111
  • 03 Nov 2026
Topic Review
NETosis in Parasitic Infections
Neutrophils are the key players in the innate immune system, being weaponized with numerous strategies to eliminate pathogens. The production of extracellular traps is one of the effector mechanisms operated by neutrophils in a process called NETosis. Neutrophil extracellular traps (NETs) are complex webs of extracellular DNA studded with histones and cytoplasmic granular proteins.
  • 1.1K
  • 03 Nov 2026

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