Leishmania (V.) braziliensis and Leishmania(L.) amazonensis are the most pathogenic agents of American Cutaneous Leishmaniasis in Brazil, causing a wide spectrum of clinical and immunopathological manifestations, including: localized cutaneous leishmaniasis (LCL^DTH+/++), borderline disseminated cutaneous leishmaniasis (BDCL^DTH±), anergic diffuse cutaneous leishmaniasis (ADCL^DTH-), and mucosal leishmaniasis (ML^DTH++++). It has recently been demonstrated, however, that while L. (V.) braziliensis shows a clear potential to advance the infection from central LCL (a moderate T-cell hypersensitivity form) towards ML (the highest T-cell hypersensitivity pole), L. (L.) amazonensis drives the infection in the opposite direction to ADCL (the lowest T-cell hypersensitivity pole). This study evaluated by immunohistochemistry the expression of Toll-like receptors (TLRs) 2, 4, and 9 and their relationships with CD4 and CD8 T-cells, and TNF-α, IL-10, and TGF-β cytokines in that disease spectrum. Biopsies of skin and mucosal lesions from 43 patients were examined: 6 cases of ADCL, 5 of BDCL, and 11 of LCL caused byL. (L.) amazonensis; as well as 10 cases of LCL, 4 of BDCL, and 6 of ML caused byL. (V.) braziliensis. CD4⁺ T-cells demonstrated their highest expression in ML and, in contrast, their lowest in ADCL. CD8⁺ T-cells also showed their lowest expression in ADCL as compared to the other forms of the disease. TNF-α⁺showed increased expression from ADCL to ML, while IL-10⁺and TGF-β⁺ showed increased expression in the opposite direction, from ML to ADCL. With regards to TLR2, 4, and 9 expressions, strong interactions of TLR2 and 4 with clinical forms associated with L. (V.) braziliensis were observed, while TLR9, in contrast, showed a strong interaction with clinical forms linked to L. (L.) amazonensis. These findings strongly suggest the ability of L. (V.) braziliensis and L. (L.) amazonensis to interact with those TLRs to promote a dichotomous T-cell immune response in ACL.

Canine visceral leishmaniasis (CVL) is recognizable by characteristic signs of disease and is highly lethal. The infection, however, may be quite inapparent in some seropositive dogs, and this has raised the polemic question as to whether or not such animals can be a source of infection for Lutzomyia longipalpis, the vector of American visceral leishmaniasis (AVL). In this study we have examined 51 dogs with acute CVL from an AVL area in Pará State, northern Brazil, and compared the parasite density, amastigotes of Leishmania (L.) infantum chagasi, in the skin, lymph node and viscera of symptomatic with that of nine asymptomatic but seropositive dogs (IFAT-IgG). Post-mortem biopsy fragments of these tissues were processed by immunohistochemistry, using a polyclonal antibody against Leishmania sp. The X² and Mann Whitney tests were used to evaluate the means of infected macrophage density (p < 0.05). There was no difference (p > 0.05) in the skin (10.7/mm² x 15.5/mm²) and lymph node (6.3/mm² x 8.3/mm²), between asymptomatic and symptomatic dogs, respectively. It was higher (p < 0.05), however, in the viscera of symptomatic (5.3/mm²) than it was in asymptomatic (1.4/mm²) dogs. These results strongly suggest that asymptomatic or symptomatic L. (L.) i. chagasi-infected dogs can serve as a source of infection, principally considering the highest (p < 0.05) parasite density from skin (10.7/mm² x 15.5/mm²), the place where the vetor L. longipalpis takes its blood meal, compared with those from lymph node (6.3/mm² x 8.3/mm²) and viscera (1.4/mm²x 5.3/mm²).

The treatment of leishmaniasis has limitations due to drug toxicity and the increasing resistance of the parasite. In this study, we analyze the role of oxidative stress in the pathogenesis and treatment of leishmaniasis, as well as in new therapeutic alternatives of natural origin. The evasion mechanisms against the host immune response involve surface molecules present in the parasite, which modulate oxidative stress to ensure its survival. Drug treatment requires strict monitoring to minimize adverse reactions and ensure patient safety, as mechanisms such as lipid peroxidation, mitochondrial dysfunction, and depletion of antioxidant defenses are associated with drug toxicity. Plant-derived products with antileishmanial activity impact the parasite’s redox balance, inducing apoptosis and reducing its parasitic load. Most studies are still in preliminary stages, making in vivo assays and clinical studies essential, along with the development of accessible formulations. Oxidative stress is involved in the pathogenesis of leishmaniasis, as Leishmania manipulates the host’s redox balance to survive. It also contributes to drug toxicity, as antimonials and amphotericin B increase reactive oxygen species, causing cellular damage. Several plant-derived compounds have demonstrated antileishmanial activity by modulating oxidative stress and promoting parasite apoptosis. Examples include alkaloids from Aspidosperma nitidum, lignans from Virola surinamensis, flavonoids from Geissospermum vellosii, and triterpenoids such as β-sitosterol. Although these compounds show promising selectivity, most studies remain in preliminary stages, requiring in vivo assays and clinical studies to confirm efficacy and safety, as well as the development of affordable formulations.

We present here a cross-sectional study analyzing the IgG1 and IgG2 immune responses to natural canine Leishmania (L.) infantum chagasi-infection and their relationships with delayed-type hypersensitivity (DTH) in 50 mongrel dogs with previous positive serodiagnoses (IFAT-IgG) (56% with subclinical status [= apparently healthy] and 44% clinically sick), living in endemic areas for visceral leishmaniasis in the Brazilian Amazon. IgG1 and IgG2 responses were measured using commercial polyclonal antibodies in ELISA, while DTH was elicited by intradermal skin test using cultured promastigotes L. (L.) i. chagasi-antigen. Data analyses used Chi-square and Pearson's r coefficient (95% confidence interval). Regarding DTH and the clinical statuses of dogs, it was noted that 100% of the animals showing positive DTH (n = 8) were from the subclinical group, while 100% showing negative DTH were from the clinically sick group; higher IgG2 than IgG1 responses were observed in both clinical groups. However, when this comparison was made between the subclinical and sick groups, higher IgG1 responses were noted in the dogs from the sick rather than the subclinical group, while no differences were noted between the IgG2 responses in the dogs from both clinical groups. Additionally, we found lower IgG1 responses in dogs from the subclinical group showing positive DTH than in the dogs from the subclinical or sick groups with negative DTH; no differences were found between the IgG2 responses of these two clinical groups. These findings suggest that the IgG1, but not the IgG2, response is associated with susceptibility to canine visceral leishmaniasis (CVL). Nous présentons ici une étude transversale analysant les réponses immunitaires IgG1 et IgG2 à l'infection canine naturelle par Leishmania (L.) infantum chagasi et leurs relations avec une hypersensibilité retardée (HR) chez 50 chiens errants avec des sérologies positives antérieures (IFAT-IgG) (56 % avec statut sous-clinique [= apparemment en bonne santé] et 44 % malades cliniquement) vivant dans une zone endémique de leishmaniose viscérale dans l'Amazonie brésilienne. Les réponses IgG1 et IgG2 ont été mesurées en utilisant des anticorps polyclonaux commerciaux en ELISA, tandis que l'HR a été provoquée par un test cutané intradermique utilisant un antigène de promastigotes cultivés de L. (L.) i. chagasi. Les analyses de données ont utilisé le coefficient de Chi-carré et Pearson (intervalle de confiance de 95 %). En ce qui concerne l'HR et les états cliniques des chiens, on a noté que 100 % (n = 8) des animaux présentant une HR positive provenaient du groupe sous-clinique, tandis que 100 % montrant une HR négative provenaient du groupe cliniquement malade. Des réponses IgG2 supérieures aux IgG1 ont été observées dans les deux groupes cliniques. Cependant, lorsque cette comparaison a été faite entre les groupes sous-clinique et malade, des réponses IgG1 plus élevées ont été observées chez les chiens du groupe malade que chez le groupe sous-clinique, alors qu'aucune différence n'a été notée entre les réponses IgG2 chez les chiens des deux groupes cliniques. En outre, nous avons trouvé des réponses IgG1 plus faibles chez les chiens du groupe sous-clinique présentant une HR positive que chez les chiens des groupes sous-cliniques ou malades avec HR négative. Aucune différence n'a été trouvée entre les réponses IgG2 de ces deux groupes cliniques. Ces résultats suggèrent fortement que la réponse IgG1, mais pas IgG2, est associée à une susceptibilité à la leishmaniose viscérale canine.