An In Vitro Feline Macrophage Model as a Tool to Study Leishmania Infection and Glucuronoxylomannan-Mediated Modulation

Feline leishmaniasis is an emerging zoonotic disease, yet the cellular and immunological mechanisms underlying Leishmania infection in cats remain poorly understood. In this study, we established and characterized Fcwf-4 feline macrophages as an in vitro model of Leishmania amazonensis infection and investigated the immunomodulatory effects of glucuronoxylomannan (GXM), the major capsular polysaccharide of Cryptococcus neoformans. Fcwf-4 macrophages were infected with L. amazonensis promastigotes and evaluated at 2, 24, and 48 h post-infection. Parasite burden, macrophage viability, nitric oxide (NO), and reactive oxygen species (ROS) production were assessed in the presence or absence of GXM. Fcwf-4 macrophages supported L. amazonensis infection throughout the experimental period, with a progressive decrease in the infection index, indicating partial control of parasite burden over time. Notably, the presence of GXM increased the infection index without compromising macrophage viability, suggesting that enhanced parasite persistence resulted from immunomodulation rather than cytotoxicity. LPS stimulation enhanced NO and ROS production, whereas L. amazonensis infection selectively reduced NO production, indicating impairment of macrophage effector responses. Further, GXM suppressed ROS production, including basal ROS levels, suggesting an additional inhibitory effect on macrophage oxidative responses. Collectively, these findings provide experimental evidence that Fcwf-4 could be useful as a tool to study feline macrophage–Leishmania interactions in vitro and co-infection-associated immunomodulation.