CD28 and common variable immunodeficiency: This is the first study comparing migratory function of granulocytes, oxidative burst activity of phagocytic cells, surface integrin expressions on neutrophils and lymphocytes, natural killer (NK) cell numbers and cytotoxic activity, natural killer T cells, lymphocyte subsets such as CD8+CD28+, CD4+CTLA-4+ cells in CVID patients (n: 20) and healthy controls (n: 26).