Interestingly, CD4+ T‐helper (TH) cells, particularly TH1 cells, are increased in the peripheral blood of PD patients (Baba et al., 2005) and TH1 cells recruit CD8+ cytotoxic T cells which are the predominant T‐cell infiltrate in the brain in PD patients at post‐mortem and in MPTP‐lesioned animals (Brochard et al., 2009), providing further support for an adaptive CD4+ TH cell mediated immune response in PD. The gene discussed is CD4; the disease is Parkinson disease.