Is tolerance innate or acquired?
The phenomenon of tolerance is present in both innate and adaptive immune systems. We are protected from the innate immune system by specific mechanisms that block its activities, such as membrane complement regulatory proteins that protect self-tissues from the alternative complement pathway. The adaptive immune system “learns” to be tolerant of some specific antigens, such as self-tissues, just as it learns to be “intolerant” of many foreign antigens. When discussing autoimmune disorders, we often narrow our perspective to the tolerance of autoantigens, such as an individual’s own nucleoproteins or cell-surface molecules, by the adaptive immune system. However, the phenomenon of tolerance is not limited to autoantigens. In fact, tolerance to exogenous antigens, such as dietary proteins, is just as crucial for the survival of an individual as “self-tolerance.”