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CTLA-4 (CD152) can inhibit T cell activation by two different mechanisms depending on its level of cell surface

B M Carreno1, F Bennett, T A Chau

  • 1Genetics Institute, Inc., Cambridge, MA 02140, USA.

Journal of Immunology (Baltimore, Md. : 1950)
|July 21, 2000
PubMed

Insights

Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4) down-regulates T cell activation through two distinct mechanisms: a negative signal requiring its cytoplasmic region or B7 sequestration, depending on cell surface levels.

Area of Science:

  • Immunology
  • Cellular Biology
  • Molecular Biology

Background:

  • Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4) is a key regulator of T cell activation.
  • Two primary mechanisms, negative signaling and competitive antagonism of CD28:B7 costimulation, have been proposed for CTLA-4's inhibitory function.

Purpose of the Study:

  • To elucidate the distinct contributions of CTLA-4's negative signaling and B7 sequestration mechanisms in T cell activation.
  • To investigate the role of the CTLA-4 cytoplasmic region in mediating these inhibitory functions.

Main Methods:

  • Utilized T cell lines engineered to express human CTLA-4 with mutations in its cytoplasmic region.
  • Assessed the impact of CTLA-4 engagement on IL-2 production under both B7-independent and B7-dependent costimulation conditions.

Main Results:

  • CTLA-4-mediated inhibition of IL-2 production under B7-independent costimulation required the CTLA-4 cytoplasmic region.
  • Under B7-dependent costimulation, CTLA-4's inhibition of IL-2 production was dependent on cell surface levels and did not require the cytoplasmic region.

Conclusions:

  • CTLA-4 employs dual mechanisms for T cell activation down-regulation: negative signaling and B7 sequestration.
  • The operational mechanism depends on CTLA-4 surface expression levels, potentially leading to rapid inhibition or T cell anergy.

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