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. 2019 Jun 6;10:609. doi: 10.3389/fphar.2019.00609

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Copyright © 2019 Liao, Wang, Liao, Li and Niu

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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T cell activation regulated by CTLA-4 and CD28. (A) Simultaneous recognition of a specific major histocompatibility complex (MHC)–peptide complex by the T cell receptor (TCR) and of CD80/CD86 by the co-stimulatory receptor CD28 results in T cell activation. Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) is a CD28 homologue expressed on the surface of T lymphocytes with higher affinity for CD80/CD86. When CTLA-4 competitively binds to CD80/CD86, signal 2 required for T cell activation reduces, which eventually leads to T cell anergy. (B) The blockade of CTLA-4 signaling restores signal 2 in response to binding of CD28 with CD80/CD86 thus promoting T cell activation and proliferation.