Nonpathogenic SIV Infection in Sooty Mangabeys Is Characterized by a Lack of Activation and Expansion of Monocytes.

INTRODUCTION: Natural hosts of simian immunodeficiency virus (SIV), including sooty mangabeys (SMs), maintain high viremia without progressing to AIDS and AIDS-associated histopathogenesis. The mechanisms underlying this protection and lack of pathogenesis remain incompletely understood, particularly in relation to monocyte/macrophage activation. METHODS: Plasma soluble CD163 (sCD163), monocyte CD163 expression, and monocyte subset phenotypes were quantified in uninfected and naturally SIV-infected SMs and compared with uninfected and SIV-infected rhesus macaques (RMs). Flow cytometry and multivariate analyses were used to assess monocyte activation and subset distribution. RESULTS: sCD163 levels and CD163 surface expression were increased in SIV-infected RMs but not SMs. SIV-infected SMs exhibited reduced CD14+CD16+ monocyte expansion and lower expression of CD64, MAC387, CD11b, and CCR2 compared with SIV-infected RMs. Machine learning identified CD14+CD16+CCR8+ monocytes as the top discriminator of SIV infection in SMs. CONCLUSION: These findings indicate a lack of monocyte activation in SMs that correlates with non-pathogenic infection.