Clonal selection is thought to cause mutations of antigen-binding affinity in memory cells during clonal expansion so that memory cells have greatly increased antigen-binding affinity than the effector cells during the first response. This assumes that random mutations resulted in lymphocytes that were autoreactive instead of reactive to non-self antigens.įollowing an adaptive immune response, memory cells are able to respond to a new infection of the same pathogen much more quickly than the original effector T cells during the formation of the adaptive immune response. Here, the body’s own epitopes are presented to the infant lymphocytes those that react are recognized as auto-reactive and destroyed before they (and their future cloned daughter cells) can leave and wreak havoc in the body. It is also assumed that most lymphocytes never encounter the antigen for which they bear a receptor.Ĭlonal selection may also be used during negative selection during T cell maturation. During antigen presentation, pre-existing lymphocytes that bear that antigen receptor are merely selected because they can bind with that antigen. The theoretical basis of clonal selection is the assumption that lymphocytes bearing an antigen receptor for an antigen exist long before antigen presentation occurs, explained by the idea of random mutations (VDJ recombination) that occur during lymphocyte maturation. This mass production is termed “clonal expansion,” in which daughter cells proliferate into several generations of clones of the original parent cells. In clonal selection, an antigen is presented to many circulating naive B and (via MHC) T cells, and the lymphocytes that match the antigen are selected to form both memory and effector clones of themselves.
Clonal selection assumes that lymphocytes are selected during antigen presentation because they already have receptors for that antigen. T and B cells are able to respond to nearly all of the world’s vast variety of antigens upon presentation. Clonal selection: The idea that lymphocytes have antigen-specific binding receptors before they encounter with an antigen, and are selected to proliferate because they have the specific antigen receptor needed during an adaptive immune response.Ĭlonal selection is an theory that attempts to explain why lymphocytes are able to respond to so many different types of antigens.Many subsets of helper T cells are created during T cell differentiation and perform vastly different functions for the immune system.During T cell differentiation, the naive T cell becomes a blast cell that proliferates by clonal expansion and differentiates into memory and effector T cells.Clonal selection may explain why memory cells can initiate secondary immune responses more quickly than the primary immune response, due to increased binding affinity from clonal expansion.After antigen presentation, selected lymphocytes undergo clonal expansion because they have the needed antigen receptor. Clonal selection is the theory that specific antigen receptors exist on lymphocytes before they are presented with an antigen due to random mutations during initial maturation and proliferation.Clonal selection is used during negative selection to destroy lymphocytes that may be able to bind with self antigens.
The thymocytes progress from double negative cells to become double-positive thymocytes (CD4+CD8+), and finally mature to single-positive (CD4+CD8- or CD4-CD8+). All T cells originate from hematopoietic stem cells in the bone marrow and generate a large population of immature thymocytes.