Ly6C

Ly6C is a member of the lymphocyte antigen 6 (Ly6) family of cell-surface proteins. It is a small, approximately 12 kDa glycosylphosphatidylinositol (GPI)-anchored glycoprotein characterized by a cysteine-rich, three-finger fold. Ly6C is encoded by a Ly6 family gene and is expressed on various leukocytes in mice, where it serves as a prominent surface marker for identifying subsets of myeloid cells.

In mice, Ly6C expression distinguishes monocyte subsets: Ly6C high (Ly6C^hi) inflammatory monocytes and Ly6C low (Ly6C^lo) patrolling monocytes. Ly6C^hi monocytes rely on CCR2 for egress from the bone marrow and are rapidly recruited to sites of infection or tissue damage, where they can differentiate into macrophages or dendritic cells. Ly6C^lo monocytes patrol the vasculature, monitor endothelial integrity, and contribute to tissue repair. The marker is also variably expressed on some dendritic cells and T cell subsets, reflecting broader roles in immune cell trafficking.

Ly6C is GPI-anchored to the cell surface and can be released by enzymatic cleavage, allowing potential soluble functions. Expression levels can be modulated during inflammation, infection, and injury, influencing recruitment and differentiation of monocyte populations.

In humans, there is no direct, widely used Ly6C homolog for routine immune phenotyping. Human monocyte subsets are typically defined by CD14 and CD16 expression. As a result, findings from Ly6C-based mouse studies require careful translation to human biology. Ly6 family members remain important tools for studying cell signaling, adhesion, and localization in the immune system.