Some of the major subsets of CD4 T cells, including their specific products (cytokines), the characteristic transcription factors and cytokines critical for their fate determination and some of their functions are summarized Figure 1A. Failure to activate an appropriate T cell response can lead to chronic infection, while exaggerated T cell responses can cause excessive tissue damage and are associated with inflammatory and autoimmune diseases. The gene discussed is CD4; the disease is autoimmune disease.