Comparative Immunopathology of Toxoplasma gondii Natural Infections in Marmosets ( Callithrix spp.) and Howler Monkeys ( Alouatta spp.), Brazil

INTRODUCTION: Neotropical primates (NTPs) present varying susceptibility to toxoplasmosis caused by Toxoplasma gondii, but their immunopathogenic responses remain poorly understood. MATERIALS AND METHODS: Local immune responses were characterized in the liver, spleen, and central nervous system (CNS) of 50 naturally infected NTPs (31 Callithrix spp.; 19 Alouatta spp.) by immunohistochemistry. Splenic white pulp morphometry, CD3+ T lymphocyte, Iba1+ macrophage/microglia, polymorphonuclear neutrophil quantification, and IFN-γ and IL-10 semi-quantification were performed. RESULTS: Both genera exhibited splenic white pulp hyperplasia. Within genera, marmosets showed predominant CD3+ infiltrates in the spleen and histiocytic infiltrates in the liver and CNS, whereas howler monkeys exhibited predominantly histiocytic infiltrates in all tissues. Between genera, marmosets had significantly higher splenic CD3+ T-cell (p < 0.05), Iba1+ macrophage (p = 0.030), and IFN-γ (p = 0.018) immunolabeling than howler monkeys.