Final answer:
The property that allows lymphocytes to not attack the body's own cells is self-tolerance. It is a crucial aspect of immune regulation, maintained by Treg cells promoting immune tolerance to avoid autoimmune reactions.
Step-by-step explanation:
The property of lymphocytes that prevents them from attacking the body's own cells is known as self-tolerance. This vital immune system function is integral to preventing autoimmune diseases where the body's immune system erroneously targets its own tissues. Within the maturation process of T and B lymphocytes, mechanisms are in place to establish immune tolerance, allowing these cells to distinguish between harmless self-antigens and potentially dangerous foreign antigens. Regulatory T (Treg) cells play a crucial role in promoting this tolerance by suppressing local inflammation and inhibiting the secretion of stimulatory immune factors, thus ensuring the immune system's focus remains on actual pathogens, not the body's own cells.