-developing called thymocytes

-derived from multipotent hematopoeitic stem cells in bone marrow that migrate to thymus for development

-rearrangment in thymus

-negative and positive selection in thymus

-immature thymocytes in cortex, mature thymocytes in medulla

-located anterior thorax, just above heart

-numerous lobules

-outer cortical region: thymic cortex

-inner cortical region: medulla

-epithelia: thymic stroma

-mutation where thymus does not form properly

-produce B cells but few T cells

-side effect of mutation: no hair

-transplant thymus grafts and T cells develop in thymus

-sever combined immunodeficiency

-absent or atypical B and/or T cells (defect in VDJ rearrangement)

-if transplant bone marrow grafts, normal T cells develop

-MHCI interaction causes CD8 expression to continue and CD4 to cease

-MHCII causes CD4 to continue and CD8 to cease