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.

Glycine, a non-essential amino acid, plays diverse biological roles, including antimicrobial and anti-inflammatory activities, cytoprotective effects, neurotransmitter functions, and potential anticancer properties. The potential of glycine supplementation in parasitic diseases, such as leishmaniasis, remains underexplored. Leishmania mexicana, a protozoan parasite, is a causative agent of cutaneous leishmaniasis, characterized by chronic lesions and significant immunopathology. This study investigates the impact of glycine supplementation on disease progression and parasite control in a BALB/c mouse model of L. mexicana infection. BALB/c mice were infected with L. mexicana and received glycine-supplemented drinking water ad libitum, beginning on the day of infection. Glycine supplementation exhibited a protective effect, as evidenced by significantly reduced lesion sizes and decreased parasite burdens. Cytokine profiling of spleen cells from glycine-treated mice revealed an immunomodulatory effect, characterized by increased interleukin-10 (IL-10) production and decreased tumor necrosis factor-alpha (TNF-α) levels upon stimulation with L. mexicana promastigote antigens. In vitro studies showed that glycine supplementation inhibited promastigote and amastigote growth in a dose-dependent manner. Macrophages cultured in glycine-enriched media showed reduced parasite recovery from infected macrophages. Importantly, no cytotoxic effects were observed in cultured host cells. Histological analysis of tissue lesions showed a lower parasite burden and diminished inflammatory infiltrate in glycine-treated mice. The histological analysis of liver and kidney tissues from glycine-supplemented mice showed no detectable histopathological alterations in liver or kidney at the tested doses. These findings suggest that glycine may represent a promising anti-Leishmania agent for controlling disease progression. Glycine’s dual ability to modulate host immune responses and directly inhibit parasite growth highlights the potential benefits of early glycine supplementation in cutaneous leishmaniasis.