Netosis is a recently described type of neutrophil death occurring with the release to the extracellular milieu of a lattice composed of DNA associated with histones and granular and cytoplasmic proteins. These webs, initially named neutrophil extracellular traps (NETs), ensnare and kill microorganisms. Similarly, other cell types, such as eosinophils, mast cells, and macrophages, can also dye by this mechanism; thus, it was renamed as ETosis, meaning death with release of extracellular traps (ETs). Here, we review the mechanism of NETosis/etosis, emphasizing its role in diseases caused by protozoan parasites, fungi, and viruses.

Feline leukemia virus (FeLV), a common, naturally occurring gammaretrovirus in domestic cats, is associated with degenerative diseases of the haematopoietic system, immunodeficiency and neoplasia. FeLV infection causes an important suppression of neutrophil function, leading to opportunistic infections. Recently, a new microbicidal mechanism named NETosis was described in human, bovine and fish neutrophils, as well as in chicken heterophils. The purpose of the present study was to characterize NETosis in feline neutrophils, as well as to evaluate neutrophil function in FeLV naturally infected symptomatic and asymptomatic cats through the phagocytosis process, release of neutrophil extracellular traps (NETs) and myeloperoxidase (MPO) activity. The results showed that feline neutrophils stimulated with protozoa parasites released structures comprising DNA and histones, which were characterized as NETs by immunofluorescence. Quantification of NETs after neutrophil stimulation showed a significant increase in NET release by neutrophils from FeLV− and FeLV+ asymptomatic cats compared with FeLV+ symptomatic cats. Moreover, the number of released NETs and MPO activity in unstimulated neutrophils of FeLV+ symptomatic cats were higher than those in unstimulated neutrophils from FeLV− and FeLV+ asymptomatic cats. This study reports, for the first time, NET release by feline neutrophils, along with the fact that NET induction may be modulated by a viral infection. The results indicate that the NET mechanism appears to be overactivated in FeLV+ cats and that this feature could be considered a marker of disease progression in FeLV infection.

Resveratrol is a polyphenol found in black grapes and red wine and has many biological activities. In this study, we evaluated the effect of resveratrol alone and in association with amphotericin B (AMB) against Leishmania amazonensis . Our results demonstrate that resveratrol possesses both antipromastigote and antiamastigote effects, with 50% inhibitory concentrations (IC ₅₀ s) of 27 and 42 μM, respectively. The association of resveratrol with AMB showed synergy for L. amazonensis amastigotes, as demonstrated by the mean sums of fractional inhibitory index concentration (mean ΣFIC) of 0.483, although for promastigotes, this association was indifferent. Treatment with resveratrol increased the percentage of promastigotes in the sub-G ₀ /G ₁ phase of the cell cycle, reduced the mitochondrial potential, and showed an elevated choline peak and CH ₂ -to-CH ₃ ratio in the nuclear magnetic resonance (NMR) spectroscopy analysis; all these features indicate parasite death. Resveratrol also decreased the activity of the enzyme arginase in uninfected and infected macrophages with and without stimulation with interleukin-4 (IL-4), also implicating arginase inhibition in parasite death. The anti- Leishmania effect of resveratrol and its potential synergistic association with AMB indicate that these compounds should be subjected to further studies of drug association therapy in vivo .

Leishmaniases is a tropical disease caused by protozoa of the genusLeishmaniafor which the current treatment is expensive, besides increasing reports of parasite resistance. This study investigated the anti-Leishmania amazonensisactivity of the essential oil fromAloysia gratissima(AgEO) and guaiol, the major sesquiterpene constituent in the oil. Our results showed that AgEO killed promastigotes and intracellular amastigotes at an IC₅₀of 25 and 0·16µg mL⁻¹, respectively, while guaiol killed amastigotes at an IC₅₀of 0·01µg mL⁻¹. Both AgEO and guaiol were safe for macrophages up to 100µg mL⁻¹, as evaluated by the dehydrogenase activity, membrane integrity and phagocytic capacity. AgEO and guaiol did not induce nitrite oxide (NO) in resting macrophages and inhibited the production of NO in lipopolysaccharide-stimulated macrophages. The ultrastructural analysis suggested that AgEO and guaiol act directly on parasites, affecting promastigotes kinetoplast, mitochondrial matrix and plasma membrane. Together, these results pointed out that AgEO and guaiol could be promising candidates to develop anti-Leishmaniadrugs.