CD4 and amyotrophic lateral sclerosis: In fact, when lacking CD4+ T cells, ALS mouse microglial cells display decreased levels of trophic factors such as insulin like growth factor 1 (IGF-1), GDNF, and BDNF; increased levels of proinflammatory cytokines such as IL-6 and TNF-α; and elevated levels of NADPH-oxidase 2, which is known to enhance microglial release of ROS (Beers et al., 2008; Chiu et al., 2008).