35. Cell-mediated immunity Flashcards
(64 cards)
pathway of how T CELLS are formed (5 steps)
1.HAEMATOPOEITIC STEM CELLS in BONE MARROW
- DIFFERENTIATE into LYMPHOID PROGENITORS
- become PRO-T CELLS which MIGRATE TO THYMUS
- known as THYMOCYTES in thymus
- MATURE to become T CELLS
how do thymocytes MATURE to become T CELLS
- creating DIVERSITY within ANTIGEN BINDING REGIONS of T cell RECEPTORS
REARRANGE T cell ANTIGEN RECEPTOR GENES RANDOMLY to form unique antigen binding pocket
REARRANGE V (variable) D (diversity) and J (joining) GENE SEGMENTS RANDOMLY
for both ALPHA and BETA CHAINS
what is EDUCATION of T CELLS
many REACT STRONGLY with SELF ANTIGENS and are DELETED
all RECEPTOR proteins on any ONE LYMPHOCYTE (clone) have
the SAME EPITOPE SPECIFICITY
majority of T CELLS express a … T CELL ANTIGEN RECEPTOR
ALPHA BETA T cell antigen receptor
(alpha and beta chains)
- CD4+
- CD8+
approx 5% of T cells express which T-cell Receptor
gamma-delta
(very low number, unclear function)
T CELLS REQUIRE
ANTIGEN PRESENTATION on MHC molecules on antigen-presenting cells or virus-infected cells
- cannot recognise free antigens
CD8+ T CELLS recognise
ENDOGENOUS antigens (inside cell)
presented on MHC CLASS I
CD4+ T CELLS recognise
EXOGENOUS antigens (captures from outside cell)
presented on MHC CLASS II
T cells develop as Thymocytes in the Thymus and interact with…
STROMAL CELLS
which ACTIVATES them
- gives rise to ALPHA BETA T cells
what is CD3
common cell surface MARKER found on ALL T-Cells
what is an Immature DOUBLE-NEGATIVE THYMOCYTE
LACKS EXPRESSION of CD4 & CD8 RECEPTORS
subdivided into expression of CD44, CD25
DN4: EXPRESS BOTH CD44, CD25
DN3: EXPRESS CD25, LACK CD44
what is an Immature DOUBLE-POSITIVE THYMOCYTE
EXPRESS CD4 & CD8 RECEPTORS
rearrange t cell receptor alpha chain loci
migrate to thymus - mature
downregulation of either CD4 or CD8
what happens to T-Cells that REACT too STRONGLY to SELF-ANTIGENS or MHC
undergo APOPTOSIS
- DELETION
what on the T cell forms a COMPLEX to recognised the presented ANTIGEN
T-cell RECEPTOR
CD8/CD4
CD3
how do T and B CELL RECEPTORS have VARIABLE REGION - UNIQUE antigen-binding pocket
by VDJ RECOMBINATIONS
SIMILARITIES between T and B CELL RECEPTORS
-CONSTANT and VARIABLE regions
- 2 DIFFERENT CHAINS
DIFFERENCES between T and B CELL RECEPTORS
B CELL:
Recognise free antigen
Receptor SECRETED (antibodies)
T CELL:
Recognise MHC-bound peptides
Not secreted
what happens when T-CELLS ENCOUNTER specific presented ANTIGEN in lymphoid tissue
becomes ACTIVATED
undergoes PROLIFERATION : CLONAL EXPANSION
& DIFFERENTIATION into
EFFECTOR CELLS and MEMORY CELLS
T cell pathway
development - maturation - activation - action
- T-cell precursors migrate from bone marrow to thymus and REARRANGE its T-cell receptor genes
- VDJ Rearrangement - SELECTION - immature T-cells that recognise self-antigens too strongly are REMOVED.
only thymocytes with LOW AFFINITY to self-antigens/MHC MATURE - Mature T-cells exit thymus and encounter foreign ANTIGEN in lymphoid organs - ACTIVATED
- PROLIFERATION and DIFFERENTIATION to eliminate infection (as either CD4+ or CD8+)
FUNCTIONS of CD8 T-CELLS
- Detect and eliminate VIRUS-INFECTED CELLS before they can shed virus particles to infect other cells
- Recognise and kill “altered-self” cells e.g. TUMOUR CELLS
- Produce CYTOTOXIC MOLECULES that trigger APOPTOSIS
- RELEASE CYTOKINES (attract macrophages)
- Recognise foreign peptides bound to MHC CLASS I proteins
- Clonal expansion and differentiation into activated cells and memory cells
how do CD8 T CELLS DESTROY TUMOURS
INDUCE APOPTOSIS
presenting ANTIGEN on MHC CLASS 1 to Naïve CD8 T CELLS causes
CLONAL EXPANSION & DIFFERENTIATION into
ACTIVATED CYTOTOXIC T CELLS
& MEMORY CYTOTOXIC T CELLS
CD8 CYTOTOXIC T-cells ELIMINATE pathogen-infected cells by releasing
CYTOLYTIC GRANULE CONTENTS:
- PERFORIN
- GRANZYMES
- GRANULYSIN
