Distinguishing self from nonself

The specific, or adaptive, immune system is characterized by memory, specificity, and the ability to distinguish self from nonself. The important cells of the adaptive immune system are the lymphocytes and antigen-presenting cells that are... 

This provides potential defensive proteins directed at almost every imaginable invader. It also ensures that every individual has a set of proteins that labels its own cells as "self," and that virtually every individual on earth has cell surface proteins different from those of every other person. In both the innate and adaptive responses the immune system must carefully distinguish "self" from "nonself."36 37 In the innate system this discrimination developed during evolution of the host and its pathogens. In the adaptive system it depends upon interaction of the T cells with surface molecules, primarily those of the major histocompatibility complex (MHC). 

T cells derive their name from the location of their production — the thymus, a small organ situated just above the heart. Examination of the developmental pathways leading to the production of mature cytotoxic and helper T cells reveals the selection mechanisms that are crucial for distinguishing self from nonself These selection criteria are quite stringent approximately 98% of the thymocytes, the precursors of T cells, die before the completion of the maturation process. 

The specific, or adaptive, immune system is characterized by memory, specificity, and the ability to distinguish self from nonself. The important cells of the adaptive immune system are the lymphocytes and antigen-presenting cells that are part of nonspecific immunity. The lymphocytes, which originate from pluripotent stem cells located in the hematopoietic tissues of the liver (fetal) and bone marrow, are composed of two general cell types T and B cells. The T cells differentiate in the thymus and are... 

Self Is Distinguished from Nonself by the Display of Peptides on Cell Surfaces... 

Note that the self-complementary and nonself-complementary processes of the same molecularity (n) give identical expressions for the van t Hoff enthalpy of the melting process, but not for the equilibrium constant. The factors in the expressions for K arise from the indistinguishability of 2A monomers in a process like A2 = 2A, while the A and B monomers in an AB = A + B process are distinguishable. 

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