The Involvement of the Omentum in Defensive Peritoneal Mechanisms: New Evidence from Dogs Naturally Infected with Leishmania infantum.

The omentum is an important immune surveillance organ located in the abdominal cavity, especially noteworthy in diseases displaying tropism for the mononuclear phagocyte system, such as canine leishmaniosis (CanL). In this context, this study aimed to evaluate the immune-inflammatory response of the omentum in dogs naturally infected with Leishmania infantum through systemic inflammatory biomarkers and anatomopathological alterations. A total of 40 dogs were investigated, comprising 10 seronegative animals and 30 symptomatic seropositive dogs with CanL. Following clinical and laboratory evaluations, median celiotomy was performed and omental samples sent to histopathological analyses. Infected dogs displayed normocytic normochromic anemia, dysproteinemia, hypoalbuminemia, hyperglobulinemia, significant reductions in albumin-to-globulin ratios (AGR), and increased neutrophil-to-albumin ratios (NAR), with these as the main inflammatory biomarkers. Microscopically, chronic inflammatory infiltrates presenting a predominant lymphoplasmacytic pattern were observed, associated with hyperemia, fibrosis, and granulomas, in addition to the presence of amastigote Leishmania spp. forms within the macrophage cytoplasm. A strong association was observed between histological inflammation grade and inflammatory pattern, whereas erythrogram parameters showed progressive reductions with increasing inflammatory grades. The omentum is, thus, noted as actively participating in CanL immunopathogenesis, acting as a potential niche for parasite persistence and a complementary indicator of systemic disease severity, while AGR and NAR demonstrate potential diagnostic and prognostic value for the clinical monitoring of canine leishmaniosis.