Researchers who studied the blood of people aged 110 and older found something that runs counter to the standard account of how the immune system ages. Instead of a uniform decline, one rare and powerful population of immune cells had expanded dramatically, with the expansion appearing to begin around age 100.
The cells are CD4 cytotoxic T lymphocytes, a hybrid type that combines the coordinating role of helper T cells with the ability to directly destroy other cells. They make up under 5 percent of T cells in most people. In this study, the median share was about 4 percent among the youngest participants, 9.6 percent among those aged 100 to 109, and 17.6 percent among those aged 110 and older.
