Immunology Unit 12

thymocytes

daughter cells in the thymus and they develop into T cells

thymus

site of T cell maturation; only lymphoid organ that does not have lymphoid follicles

cortico-medullary junction

where thymocytes start

thymic nurse cells

hold thymic lymphoblasts and induce them to become thymocytes; without these cells there is no development of thymocytes

thymic stroma

also known as thymic nurse cells

DN2 thymocytes

found in the capsular region of the cortex; these are not yet committed cells if taken out of the thymus

CD44+/CD25+ double negative thymocytes

DN2

DN3

CD44-/CD25+ pre-TCR+ double negative thymocytes

pre-T cell receptor

expresses the TCR beta and pre-T cell receptor alpha which allows for assembly and testing of the functional rearrangement of TCR beta

B cells

have two attempts at VDJ

T cells

have four attempts since there are two constant gene segments each with their own D and J segments

DN4

CD44 double negative thymocytes

TCR alpha

rearranges both genes at the same time; allows for very rapid screening of the genes; continues until both alleles are no longer able to be recombined until positive selection occurs

nonfunctional TCR

many of the TCRs that are generated will no longer recognize MHC at all

positive selection

screens for TCRs that can interact with MHC class I or MHC class II; if the cell cannot interact properly with the cortical epithelial cells then they will undergo apoptosis

autoreactive TCR

TCR is generated and reacts to host antigens

negative selection

screens TCRs that interact with host antigen displayed by antigen presenting cells in the thymus

cortical epithelial cells

function as antigen presenting cells expressing both MHC class I and MHC class II with a variety of host peptides; important for positive selection

single positive thymocytes

screened for interaction with MHC class I or class II; results in either a CD4 or CD8 T cell

dendritic cells

screen thymocytes as they enter to medulla from the cortex

medullary epithelial cells, macrophages, and dendritic cells

all express MHC class I and MHC class II; express B7 to interact with CD28; phagocytic and internalize antigen

AIRE

gene known as an autoimmune regulator; important for the expression of non-thymic genes in the thymus

hassall’s corpuscle

contain degenerating epithelial cels rich in high molecular weight cytokeratins; important for generating self antigens presented by neighboring dendritic cells

regulatory T cells

very small population of autoreactive T cells that inhibit T cell responses in the periphery; leave as memory cells

invariant NKT cells

bind to CD1 recognize lipid antigens and leave thymus as memory cells

peripheral tolerance

interacts too strongly with dendritic cells and become anerguc or undergo apoptosis

gamma delta T cells

do not express CD4 or CD8; not MHC class restricted; subgroups of both innate and adaptive; important for detecting epithelial stress and promoting inflammation

15

peak size of thymus is at this age; after this very few mature T cells are produced

tolerance

lack of immune response to self antigens

auto-antigens

self-antigens are also known as this

autoimmunity

immunity to self anitgens is known as this

autoimmune polyglandular syndrome

lack of central tolerance in the thymus; autoimmune disease affecting multiple glands of the bod; reduced thyroid function, stunted growth, abnormal puberty, etc.

rheumatoid factor

antibodies to self IgG

rheumatoid arthritis

chronic inflammation but is normally short lived as the immune complexes are rapidly cleared and stimulation of B cells ceases

immunologically privileged sites

some areas of the body that do not allow for entry of immune cells; unless damage or severe infections these areas see little immune cells

sympathetic opthalmia

one eye is damaged/ruptured and an immune response develops that leads to an autoimmune response to the second eye; can lead to total blindness

CD4+/CD25+ regulatory T cells

recognize self-anitgen; function by supressing the immune response mediated by thymocytes and anitgen presenting cells

TH3 and TR1 cells

found in mucosal immune system; important for oral tolerance to the food we ear and to a very limited extent of our normal flora

clonal exhaustion

chronic infections, persistent antigen can lead to reduced T cell function; prevents a never ending immune response