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CD Markers

CD28


Reviewers: Nat Pernick, M.D. (see Reviewers page)
Revised: 20 January 2011, last major update January 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

General
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● Receptor important in CD4+ T cell activation

Physiology
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● T cells require 2 signals for full activation: (1) binding of the antigen/MHC complex on the antigen presenting cell to the T cell receptor; (2) interaction of CD28 with its ligands CD80 (B7-1) or CD86 (B7-2), found on activated B cells and called a costimulation signal
● The costimulatory signal induces T cell activation and survival, interleukin-2 production, T-helper type 2 development and clonal expansion
● CD28 is a constitutive, high abundance, low affinity receptor; its binding also increases expression of CTLA4 (CD152), a structurally related cell surface receptor on T cells which competes with CD28 for the same ligands, but has opposite effects (J Clin Immunol 2002;22:1, Curr Pharm Des 2006;12:149)
● CD8+, CD28+ T cells are antigen specific cytotoxic T cells (class I restricted), and constitute 90% of CD8+ T cells
● CD8+, CD28- T cells are suppressor T cells; increased in various infectious diseases and autoimmune diseases and associated with aging

Diagrams
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Costimulation

Competition between CTLA4 and CD28 for same ligands

   

CD28 costimulation is also required for proper memory cell activation

Clinical features
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● An imbalance in CTLA-4/CD28 expression at the maternal-fetal interface may confer susceptibility to unexplained pregnancy loss (Int J Gynaecol Obstet 2006;93:123)
● Loss of T cell CD28 expression is associated with aging, and the frequency of CD28(null) T cells predicts immune incompetence in elderly; these T cells are functionally active and long-lived, but have no/limited proliferative capacity (Trends Immunol 2009;30:306)

Uses
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● No significant clinical use by pathologists

Positive staining - normal
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● CD4+ T cells (95%), CD8+ T cells (50%); activated B cells, thymocytes, plasma cells (some)

Positive staining - disease
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● Myeloma (95%)

Additional references
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MIM 186760, Blood 2005;105:13

End of CD Markers > CD28


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