CD Markers
CD28

Author: Nat Pernick, M.D. (see Authors page)

Revised: 22 December 2015, last major update September 2014

Copyright: (c) 2003-2015, PathologyOutlines.com, Inc.

PubMed Search: CD28[title]

Definition / General
  • Receptor important in CD4+ T cell activation, IL2 production and T helper 2 development (OMIM #186760)
  • Plays a critical role in controlling the adaptive arm of the immune response (Blood 2005;105:13)
Pathophysiology
  • 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; loss of CD28 expression in T cells is associated with various infectious and autoimmune diseases and aging:
Diagrams / Tables

Costimulation

Competition between CTLA4 and CD28 for same ligands

CD28 costimulation is also required for proper memory cell activation

Clinical Features
Uses by Pathologists
  • No significant clinical use by pathologists
Positive Staining - Normal
  • CD4+ T cells (95%), CD8+ T cells (50%); activated B cells, thymocytes and plasma cells (some)
Positive Staining - Disease