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. Author manuscript; available in PMC: 2013 Apr 1.
Published in final edited form as: Curr Opin Immunol. 2012 Jan 9;24(2):207–212. doi: 10.1016/j.coi.2011.12.009

Figure 1.

Figure 1

PD-1 and CTLA-4 play distinct roles in regulating T cell immunity. CTLA-4 modulates the early phases of activation of naïve or memory T cells in response to TCR stimulation by MHC-peptide complexes displayed by antigen presenting cells (“signal 1”). In contrast, PD-1 is expressed on antigen-experienced T cells in the periphery, and serves to limit the activity of T cells at the time of an inflammatory response, thereby protecting normal tissues from collateral destruction. DC, dendritic cell.