CD28 and CTLA4 coordinately regulate airway inflammatory cell recruitment and T-helper cell differentiation after inhaled allergen.

Airway inflammation after inhaled allergen exposure requires the recruitment, activation, and differentiation of antigen-specific T cells into T helper (Th) 2 effector cells. These processes are regulated not only by antigen engagement of the T-cell receptor, but also by specific accessory molecules on the surface of the T cell. We examined how the balance of signals derived through the CD28 and cytotoxic T-lymphocyte antigen (CTLA) 4 receptors modulate the outcome of inhaled antigen exposure in a murine model of allergic airway inflammation. Mice deficient in CD28 have defective Th2 cell development and failed to develop inflammation after sensitization and inhaled challenge with ovalbumin. Prevention of B7-CTLA4 interactions in CD28-deficient mice restored lymphocyte but not eosinophil recruitment to the airway. Analysis of cytokine gene expression revealed that T cells from CD28-deficient mice failed to differentiate into Th2 cells in either the presence or absence of B7-dependent signals, and therefore did not recruit eosinophils to the airway. Thus, the processes of T-cell recruitment to the airway and T-cell differentiation have distinct requirements for signals mediated through the CD28 and CTLA4 receptors, demonstrating that these receptors are important regulatory components in the development of allergic airway inflammation.