CD28 and idiopathic pulmonary fibrosis: Fibroblasts express MHC-I and MHC-II and can cross-present antigens to T cells; however, fibroblasts lack expression of typical costimulatory molecules CD80/86 and IPF T cells exhibit much lower expression of CD28 (81), making IPF fibroblasts unable to activate T cells but rather able to induce T cell anergy or Treg cells (82).