To investigate the modulatory effect of B-1 cells on murine peritoneal macrophages infected with Leishmania major (L. major) in vitro. Peritoneal macrophages obtained from BALB/c and BALB/c XID mice were infected with L. major and cultured in the presence or absence of B-1 cells obtained from wild-type BALB/c mice. Intracellular amastigotes were counted, and interleukin-10 (IL-10) production was quantified in the cellular supernatants using an enzyme-linked immunosorbent assay. The levels of the lipid mediator prostaglandin E2 (PGE₂) were determined using a PGE₂ enzyme immunoassay kit (Cayman Chemical, Ann Arbor, MI), and the number of lipid bodies was quantified in the cytoplasm of infected macrophages in the presence and absence of B-1 cells. Culturing the cells with selective PGE₂-neutralizing drugs inhibited PGE₂ production and confirmed the role of this lipid mediator in IL-10 production. In contrast, we demonstrated that B-1 cells derived from IL-10 KO mice did not favor the intracellular growth of L. major. We report that B-1 cells promote the growth of L. major amastigotes inside peritoneal murine macrophages. We demonstrated that the modulatory effect was independent of physical contact between the cells, suggesting that soluble factor(s) were released into the cultures. We demonstrated in our co-culture system that B-1 cells trigger IL-10 production by L. major-infected macrophages. Furthermore, the increased secretion of IL-10 was attributed to the presence of the lipid mediator PGE₂ in supernatants of L. major-infected macrophages. The presence of B-1 cells also favors the production of lipid bodies by infected macrophages. In contrast, we failed to obtain the same effect on parasite replication inside L. major-infected macrophages when the B-1 cells were isolated from IL-10 knockout mice. Our results show that elevated levels of PGE₂ and IL-10 produced by B-1 cells increase L. major growth, as indicated by the number of parasites in cell cultures.

Cryptococcus neoformans is a lethal fungus that primarily affects the respiratory system and the central nervous system. One of the main virulence factors is the capsule, constituted by the polysaccharides glucuronoxylomannan (GXM) and glucuronoxylomanogalactan (GXMGal). Polysaccharides are immunomodulators. One of the target cell populations for modulation are macrophages, which are part of the first line of defense and important for innate and adaptive immunity. It has been reported that macrophages can be modulated to act as a “Trojan horse,” taking phagocytosed yeasts to strategic sites or having their machinery activation compromised. The scarcity of information on canine cryptococcosis led us to assess whether the purified capsular polysaccharides from C. neoformans would be able to modulate the microbicidal action of macrophages. In the present study, we observed that the capsular polysaccharides, GXM, GXMGal, or capsule total did not induce apoptosis in the DH82 macrophage cell line. However, it was possible to demonstrate that the phagocytic activity was decreased after treatment with polysaccharides. In addition, recovered yeasts from macrophages treated with polysaccharides after phagocytosis could be cultured, showing that their viability was not altered. The polysaccharides led to a reduction in ROS production and the mRNA expression of IL-12 and IL-6. We observed that GXMGal inhibits MHC class II expression and GXM reduces ERK phosphorylation. In contrast, GXMGal and GXM were able to increase the PPAR-γ expression. Furthermore, our data suggest that capsular polysaccharides can reduce the microbicidal activity of canine macrophages DH82.

Cryptococcus neoformans is a fungus that mainly affects the respiratory system and the central nervous system. One of the main virulence factors is the capsule, constituted by the polysaccharides glucuronoxylomannan (GXM) and glucuronoxylomanogalactan (GXMGal). Polysaccharides are immunomodulators. One of the target cell populations for modulation are macrophages, part of the first line of defense, important for innate and adaptive immunity. It has been reported that macrophages can be modulated to act as a "Trojan horse" taking phagocytosed yeasts to strategic sites or having their machinery activation compromised. The scarcity of information on canine cryptococcosis led us to assess whether the purified capsular polysaccharides from C. neoformans would be able to modulate the microbicidal action of macrophages. In the present study, we observed that the capsular polysaccharides, GXM, GXMGal or capsule total did not present toxic effects for the DH82 macrophage cell line. However, it was possible to demonstrate that phagocytic activity was decreased after treatment with polysaccharides. In addition, yeasts recovered from macrophages treated with the polysaccharides, after phagocytosis, could be cultured, showing that their viability was not altered. The polysaccharides led to a reduction in ROS production and the expression of IL-12 and IL-6. We observed that GXMGal inhibits MHC class II expression and GXM reduces ERK phosphorylation. In contrast, GXMGal and GXM were able to increase the PPAR- expression. Furthermore, our data suggests that capsular polysaccharides can reduce the microbicidal activity of canine macrophages DH82.

Cryptococcosis is a disease originating in the lungs, often seen in immunosuppressed patients. In severe cases, it can lead to meningoencephalitis and can be fatal. Biochemical studies have shown that the capsule of Cryptococcus neoformans is predominantly composed of glucuronoxylomannan (GXM), with glucuronoxylomannogalactan (GXMGal) present in smaller amounts. These polysaccharides have different effects on the immune system, with GXM mainly having anti-inflammatory properties, while GXMGal is more pro-inflammatory. Myeloid-derived suppressor cells (MDSCs) are a diverse group of immature myeloid cells, including progenitor cells and precursors of macrophages, granulocytes, and dendritic cells at different stages of development. MDSCs are known to suppress immune responses in various diseases, including bacterial and fungal infections, through mechanisms such as the inhibition of T cell proliferation. In this study, we show that infection with either B3501 or CAP67 strains results in the accumulation of granulocytic MDSC precursors in bronchoalveolar cavities. The MDSCs recruited by the B3501 strain suppress T cell proliferation, while those recruited by the CAP67 strain do not. Furthermore, we observed the expression of PD-L1 on these MDSCs, suggesting a potential mechanism of immunosuppression during infection. These findings reveal how the polysaccharides of C. neoformans might weaken the host’s immune defense.

Leishmania spp. are obligatory intracellular parasites that primarily infect macrophages. The macrophage immune response plays a pivotal role in determining the control or progression of infection. “M1-like” macrophages mediate parasite clearance through the production of nitric oxide, pro-inflammatory cytokines, and reactive oxygen species, whereas “M2-like” macrophages contribute to infection progression by exerting anti-inflammatory effects. The capsular polysaccharides Glucuronoxylomannan (GXM) and glucuronoxylomannogalactan (GXMGal) from Cryptococcus neoformans are capable of immunomodulating the macrophage response. GXM exhibits immunoregulatory activity, whereas GXMGal induces a pro-inflammatory response. Although the activity of these polysaccharides has been studied in cryptococcosis, their immunomodulatory potential in other infectious models remains largely unexplored. Here, we investigated the effects of GXM and GXMGal on Leishmania major infection in murine peritoneal macrophages. Murine peritoneal macrophages were infected with L. major and, 24 h post-infection, treated with 50 μg of either GXM or GXMGal. Our data revealed that GXM treatment enhanced L. major infection, while GXMGal treatment had no significant effect on the parasitic load in infected macrophages.

The interactions between cell and cellular matrix confers plasticity to each body tissue, influencing the cellular migratory capacity. Macrophages rely on motility to promote their physiological function. These phagocytes are determinant for the control of invasive infections, and their immunological role largely depends on their ability to migrate and adhere to tissue. Therefore, they interact with the components of the extracellular matrix through their adhesion receptors, conferring morphological modifications that change their shape during migration. Nevertheless, the need to use in vitro cell growth models with the conditioning of three-dimensional synthetic matrices to mimic the dynamics of cell-matrix interaction has been increasingly studied. This becomes more important to effectively understand the changes occurring in phagocyte morphology in the context of infection progression, such as in Chagas disease. This disease is caused by the intracellular pathogen Trypanosoma cruzi, capable of infecting macrophages, determinant cells in the anti-trypanosomatid immunity. In the present study, we sought to understand how an in vitro extracellular matrix model interferes with T. cruzi infection in macrophages. Using different time intervals and parasite ratios, we evaluated the cell morphology and parasite replication rate in the presence of 3D collagen I matrix. Nevertheless, microscopy techniques such as scanning electron microscopy were crucial to trace macrophage-matrix interactions. In the present work, we demonstrated for the first time that the macrophage-matrix interaction favors T. cruzi in vitro replication and the release of anti-inflammatory cytokines during macrophage infection, in addition to drastically altering the morphology of the macrophages and promoting the formation of migratory macrophages.