Ly6C super(+) monocyte efferocytosis and cross-presentation of cell-associated antigens

Recently it was shown that circulating Ly6C super(+) monocytes traffic from tissue to the draining lymph nodes (LNs) with minimal alteration in their overall phenotype. Furthermore, in the steady state, Ly6C super(+) monocytes are as abundant as classical dendritic cells (DCs) within the draining LNs, and even more abundant during inflammation. However, little is known about the functional roles of constitutively trafficking Ly6C super(+) monocytes. In this study we investigated whether Ly6C super(+) monocytes can efferocytose (acquire dying cells) and cross-present cell-associated antigen, a functional property particularly attributed to Batf3 super(+) DCs. We demonstrated that Ly6C super(+) monocytes intrinsically efferocytose and cross-present cell-associated antigen to CD8 super(+) T cells. In addition, efferocytosis was enhanced upon direct activation of the Ly6C super(+) monocytes through its corresponding TLRs, TLR4 and TLR7. However, only ligation of TLR7, and not TLR4, enhanced cross-presentation by Ly6C super(+) monocytes. Overall, this study outlines two functional roles, among others, that Ly6C super(+) monocytes have during an adaptive immune response.