Naslov
Dynamics of positive and negative selection in the thymus: review and hypothesis

Autori
Marušić-Galešić, Suzana ; Pavelić, Krešimir

Izvornik
Immunology letters (0165-2478) 24 (1990), 3; 149-154

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
thymus ; selection

Sažetak
T cells recognized with a single receptor both a product of antigens processed by antigen presenting cells (APC1) and a self-marker molecule, encoded by the major histocompatibility complex (MHC, a property termed MHC-restricted recognition of antigen) [1–5]. During their differentiation in the thymus, T cells “learn” what to regard as self-MHC molecules, and only the cells once able to recognized antigen in the context of self-MHC will be “positively selected” to exit the thymus. The cells, once capable of reacting to self molecules, do not exit the thymus They are “negatively selected” (deleted). Both “positive” and “negative” selection depends on the T-cell-receptor (TCR) specificity. Furthermore, the TCR specificity determines the final phenotype of the mature T cells ; namely, the cells with receptors specific for the MHC-class I molecule will acquire the CD4−CD8+ phenotype, while the cells with receptors specific for the MHC-class II molecule will acquire the CD4+ CD8− phenotype. However, a few mature T cells in the periphery do not follow the rule: CD4 expression class II restriction and CD8 expression class I restriction. We believe that these T lymphocytes have a receptor with very high affinity for one class of MHC molecules and crossreact with another class of MHC molecules (with somewhat lower affinity). The majority of T lymphocytes with such receptors bind the thymic MHC molecule, for which they have the highest affinity. Since this affinity is too high for further differentation, such clones are deleted in the thymus. However, a small fraction of these cells bind the alternative class of MHC molecules, due to cross-reactivity of their receptors. This interaction allows positive selection of the cells and leads to the expression of an accessory molecule specific for the MHC molecule which mediated differentiation.

Izvorni jezik
Engleski

Znanstvena područja
Temeljne medicinske znanosti

POVEZANOST RADA