Splenic macrophage functional profile and its role in the immunopathogenesis of canine visceral leishmaniasis.

Introduction: Visceral leishmaniasis (VL) represents a major public health challenge, with the spleen frequently identified as one of the primary target organs. Dogs recognized as urban reservoir hosts, commonly harbor chronic infections characterized by elevated parasite burdens across multiple tissues. This study aims to analyze functional markers of M1 and M2 responses, as well as PD-L1+ macrophages in the spleens of naturally infected dogs with Leishmania infantum, and to correlate these findings with splenic white pulp disorganization, parasitic load, and clinical severity. Methods: Thirty-four VL-infected dogs were enrolled, each undergoing clinical evaluation to determine a clinical severity score. Histopathological analyses were performed to evaluate splenic white pulp disorganization, while quantitative PCR and immunohistochemistry were employed to assess parasite burden. Immunological markers were analyzed via immunohistochemistry, immunofluorescence, and flow cytometry. Results: Splenic white pulp disorganization was observed in most animals, indicating marked tissue disruption. Immunostaining demonstrated the presence of NOS2 Conclusion: The persistent presence of CD206, CD68