Neutrophil extracellular traps (NETs) are a defense mechanism against pathogens. They are composed of DNA and various proteins and have the ability to hinder microbial spreading and survival. However, NETs are not only related to infections but also participate in sterile inflammatory events. In addition to DNA, NETs contain histones, serine proteases, cytoskeletal proteins and antimicrobial peptides, all of which have immunomodulatory properties that can augment or decrease the inflammatory response. Extracellular localization of these molecules alerts the immune system of cellular damage, which is triggered by recognition of damage-associated molecular patterns (DAMPs) through specific pattern recognition receptors. However, not all of these molecules are DAMPs and may have other immunophysiological properties in the extracellular space. The release of NETs can lead to production of pro-inflammatory cytokines (due to TLR2/4/9 and inflammasome activation), the destruction of the extracellular matrix, activation of serine proteases and of matrix metallopeptidases (MMPs), modulation of cellular proliferation, induction of cellular migration and adhesion, promotion of thrombogenesis and angiogenesis and disruption of epithelial and endothelial permeability. Understanding the dynamics of NET-associated molecules, either individually or synergically, will help to unravel their role in inflammatory events and open novel perspectives for potential therapeutic targets. We here review molecules contained within NETS and their immunophysiological roles.

Exosomes are extracellular microvesicles of endosomal origin (multivesicular bodies, MVBs) constitutively released by eukaryotic cells by fusion of MVBs to the plasma membrane. The exosomes from Leishmania parasites contain an array of parasite molecules such as virulence factors and survival messengers, capable of modulating the host immune response and thereby favoring the infection of the host. We here show that exosomes of L. mexicana amastigotes (aExo) contain the virulence proteins gp63 and PP2C. The incubation of aExo with bone marrow‐derived macrophages (BMMs) infected with L. mexicana led to their internalization and were found to colocalize with the cellular tetraspanin CD63. Furthermore, aExo inhibited nitric oxide production of infected BMMs, permitting enhanced intracellular parasite survival. Expressions of antigen‐presenting (major histocompatibility complex class I, MHC‐I, and CD1d) and costimulatory (CD86 and PD‐L1) molecules were modulated in a dose‐dependent fashion. Whereas MHC‐I, CD86 and PD‐L1 expressions were diminished by exosomes, CD1d was enhanced. We conclude that aExo of L. mexicana are capable of decreasing microbicidal mechanisms of infected macrophages by inhibiting nitric oxide production, thereby enabling parasite survival. They also hamper the cellular immune response by diminishing MHC‐I and CD86 on an important antigen‐presenting cell, which potentially interferes with CD8 T cell activation. The enhanced CD1d expression in combination with reduction of PD‐L1 on BMMs point to a potential shift of the activation route towards lipid presentations, yet the effectivity of this immune activation is not evident, since in the absence of costimulatory molecules, cellular anergy and tolerance would be expected.

Porphyromonas gingivalis is a keystone pathogen associated with periodontitis development, a chronic inflammatory pathology characterized by the destruction of the supporting teeth structure. Macrophages are recruited cells in the inflammatory infiltrate from patients with periodontitis. They are activated by the P. gingivalis virulence factors arsenal, promoting an inflammatory microenvironment characterized by cytokine production (TNF-α, IL-1β, IL-6), prostaglandins, and metalloproteinases (MMPs) that foster the tissular destruction characteristic of periodontitis. Furthermore, P. gingivalis suppresses the generation of nitric oxide, a potent antimicrobial molecule, through its degradation, and incorporating its byproducts as a source of energy. Oral antimicrobial peptides can contribute to controlling the disease due to their antimicrobial and immunoregulatory activity, which allows them to maintain homeostasis in the oral cavity. This study aimed to analyze the immunopathological role of macrophages activated by P. gingivalis in periodontitis and suggested using antimicrobial peptides as therapeutic agents to treat the disease.

Morales-Primo AU, et al. Immune Netw. 2024 Mar;24(2):e14. https://doi.org/10.4110/in.2024.24.e14

Pentavalent antimonials are the first-line treatment for localized cutaneous leishmaniasis. However, they have disadvantages such as their elevated toxicity, high costs, and parenteral application. Plant-derived compounds may be an alternative treatment against this disease. Previous in vitro studies have shown that (3S)-16,17-didehydrofalcarinol (1), a polyacetylene oxylipin isolated from Tridax procumbens, is active against Leishmania mexicana. We have analyzed the mechanism of action of compound 1, evaluating reactive oxygen species production, apoptosis of L. mexicana, cytotoxicity in murine macrophages, and its efficacy in controlling the disease progression and parasite load when applied topically in C57BL/6 mice infected with L. mexicana. Results show that parasites incubated with 1.6 μM compound 1 significantly increased reactive oxygen species production (p ≤ 0.05). The percentage of apoptosis also increased significantly (p ≤ 0.05) and did not affect the viability of macrophages. The application of the topical formulations with 0.5% and 0.75% compound 1 for 7 weeks reduced disease progression and parasite load. We demonstrate that compound 1 generates the death of L. mexicana by apoptosis through reactive oxygen species production. We conclude that compound 1 can be used a possible alternative treatment for localized cutaneous leishmaniasis, enabling a less painful and more accessible therapy.