Relationships between Distinct Blood Monocyte Subsets and Migrating Intestinal Lymph Dendritic Cells In Vivo under Steady-State Conditions

Abstract

The origins of dendritic cells (DCs) are poorly understood. In inflammation, DCs can arise from blood monocytes (MOs), but their steady-state origin may differ, as shown for Langerhans cells. Two main subsets of MOs, defined by expression of different chemokine receptors, CCR2 and CX3CR1, have been described in mice and humans. Recent studies have identified the inflammatory function of CCR2highCX3CR1low MOs but have not defined unambiguously the origin and fate of CCR2lowCX3CR1high cells. In this study, we show that rat MOs can also be divided into CCR2highCX3CR1low(CD43low) and CCR2lowCX3CR1high(CD43high) subsets with distinct migratory properties in vivo. Using whole body perfusion to obtain MOs, including the marginating pool, we show by adoptive transfer that CD43low MOs can differentiate into CD43high MOs in blood without cell division. By adoptive transfer of blood MOs followed by collection of pseudoafferent lymph, we show for the first time that a small proportion of intestinal lymph DCs are derived from CCR2lowCX3CR1high(CD43high) blood MOs in vivo under steady-state conditions. This study confirms one of the possible origins of CCR2lowCX3CR1high blood MOs and indicate that they may contribute to migratory intestinal DCs in vivo in the absence of inflammatory stimuli.