Lecture 10: T Cells

Question 1

what does CD stand for

Answer 1

cluster determinant

Question 2

what are the types of T cells

Answer 2

• CD4 helper

- CD8 cytotoxic

Question 3

where are T cells found

Answer 3

• produced in bone marrow

- migrate to thymus during infection

Question 4

what is the role of the thymus

Answer 4

educates thymocytes:

• selection of cells that are likely to be useful
• removal of cells that are likely to be self reactive

Question 5

features of T cell receptors

Answer 5

• constant region that interacts with lymphocyte
• variable region that interacts with antigen and produced by somatic recombination
• receptor fixed on surface of T cell
• recognises peptides of antigens, presented by MHC molecules

Question 6

what is the class I pathway

Answer 6

• host cell synthesises viral proteins and passes them through the ER and Golgi to the cytoplasm
• a sample of these passes through the proteosome
• proteins degraded into peptides and transported back to ER through TAP transporter
• in ER, peptides loaded onto MHCI molecules
• CD8 T cell recognises peptide as foreign and kills target cell

Question 7

what is a proteosome

Answer 7

tubular organelle lined with digestive enzymes

Question 8

what is the class II pathway

Answer 8

• macrophages and dendrite cells sample antigens from extracellular space by endocytosis
• antigen taken into intracellular vesicles containing proteases which degrade the antigen into peptide fragments
• these vesicles fuse with vesicles containing MHCII molecules
• present these to CD4 T cells

Question 9

how do B cells present antigens

Answer 9

• antigen is bound by B cell surface receptor
• antigen internalised and degraded into peptide fragments
• fragments bind to MHCII and are transported to cell surface
• are antigen-specific, so only present antigens that bind to their antibody receptor

Question 10

how do CD4 cells help in B cell maturation

Answer 10

• when activated by the class II pathway, T cells provide signals to B cells via cytokines and juxtacrine signalling
• stimulates B cell to respond to antigen, proceed to affinity maturation and switch to another isotype

Question 11

how do CD4 T cells help macrophages

Answer 11

• if a macrophage is unable to kill a pathogen, it presents the antigens on its surface which are recognised by CD4 T cell
• activates macrophage by cytokine and juxtacrie signalling
• macrophages fuse to form giant multinucleated cell which makes granulomas

Question 12

what is T cell clonal selection like

Answer 12

• like B cells, T cells with the most compatible receptors are selected for survival and after infection a few remain as memory cells
• however, receptors don’t mutate like in B cells

Question 13

contrast innate immunity and adaptive immunity

Answer 13

I: granulocytes, NK cells, barriers and soluble mediators
A: T and B cells
I: recognises antigens non-specifically using PRRs
A: recognises antigens specifically
I: receptors germline-encoded
A: receptors produced by somatic recombination
I: receptors are same on all cells
A: receptors clonally selected

Question 14

contrast B cells and T cells

Answer 14

B: develop in bone marrow
T: originate in bone marrow, develop in thymus
B: recognise whole antigen
T: recognise peptide from processed antigen
B: receptor on cell surface and secreted into blood
T: receptor on cell surface only
B: mutate receptor during affinity maturation
T: no mutation

Question 15

contrast MHC class I and II

Answer 15

I: present in all nucleated cells
II: only in antigen presenting cells
I: presents intracellular antigen 
II: presents extracellular antigen
I: assembled and located in ER
II: assembled in ER, located in endosomes