BIOL 2005 Lecture Notes - Thymocyte, T-Cell Receptor, Clonal Deletion
30 Jan 2013
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Document Summary
Tolerance unresponsiveness to a particular ag (usually self) self-tolerance is learned by developing immune system. Freemartin condition in twin cattle: burnet hypothesis dizygotic twins sharing a placenta will therefore share rbc"s developing/immature lymphocytes are subject to clonal. Deletion in presence if self-antigens are recognized must occur during fetal development or early neonatal period after that, ability to become tolerance falls off rapidly. T-cells more important than b-cells for tolerance. Central tolerance generated during lymphocyte development involves clonal deletion. Peripheral tolerance generated after lymphocytes have matured involves anergy (inactivation) T-cell development: occus in thymus in 3 stages: tcr gene rearrangments resulting in productive a /b dimers on cell surface have many more v/j segments than g /d. This prevents a /b and g /d co-expression and g /d. Positive selection recognize foreign antigens in presence of self mhc: acquisition of mature effector function either cd4 or cd8 is inactivated a d. Negative selection occurs after tcr receptor expression.
