Cytotoxic T-lymphocyte associated protein 4

Cytotoxic T-lymphocyte associated protein 4, (CTLA-4) also known as CD152 (cluster of differentiation 152), is a protein receptor that functions as an immune checkpoint and downregulates immune responses. CTLA-4 is constitutively expressed in regulatory T cells but only upregulated in conventional T cells after activation – a phenomenon which is particularly notable in cancers.

Source: Wikipedia — Cytotoxic T-lymphocyte associated protein 4 (CC BY-SA 4.0)