The peripheral T cell compartment consists of quiescent “naïve” cells that are characterized by surface expression of CD62L, “activated” cells that express CD44 in response to external stimulating signals [such as antigen or cytokines released in response to lymphopenia (43)], and “memory phenotype” cells that have completed homeostatic proliferation and express both CD62L and CD44. This evidence concerns the gene SELL and lymphopenia.