CD28 and generalized anxiety disorder: The majority of research studies have demonstrated that patients with GAD have higher than normal blood levels of inflammatory cytokines, that the degree of clinical anxiety symptoms is significantly and positively correlated with the patient’s age (33), peripheral blood levels of IL-2, IL-4, and TF-alpha, and that CD28+ CD4+ T cells inhibit persistent inflammatory processes, thereby reducing the negative symptoms associated with GAD (34).