Summary T cell development

T Cell Development

 Stem cells are in the bone marrow and differentiate into precursor cells
 These migrate to the thymus
 In the thymus they undergo TCR recombination, positive and negative selection
 The mature T cells then migrate to secondary lymphatic organs like the blood,
lymph nodes and spleen

Positive and Negative Selection

 Selection between T helper and cytotoxic T may be down to microRNAs
 Thymocytes start off as CD4/CD8-
 TCR-β chain recombination takes place and thymoxytes become CD4/CD8+
 TCR-α chain recombination takes place and thymoxytes become CD4/CD8/TCR+
 Positive and negative selection then takes place
 T helper cells are CD4+/CD8-/TCR+
 Cytotoxic T cells are T helper cells are CD4-/CD8+/TCR+
 TCR and MHC binding:
 No selection due to no binding= T cell apoptosis
 Negative selection is due to strong binding= T cell apoptosis
 Positive selection is due to weak binding=T cell survival
 Aim is to produce T cells that wont recognise self MHC molecules so have a weak
affinity

Secondary Lymphatic Organs




 T cells in lymph activated by dendritic cells that migrate from infected sites

, Dendritic Cells

 Best antigen presenting cell for T cells
 Immature cells are in tissue
 Mature cells in lymph tissue
 Stimulated through cytokines like TNF




 Receptors: MHC-1, MHC-II, ICAM-1, ICAM-II, LFA-1 and B7.1

How Are TCRs Activated




Co-Stimulation of T Cells