T cell Recognition of Antigens

Question 1

what are the 3 types of professional APCs?

Answer 1

DCs, macrophages, B cells

Question 2

where do T cells “monitor” for antigens?

Answer 2

intracellular compartments

Question 3

where does T-cell development occur?

Answer 3

thymus

Question 4

what is the makeup of TCRs?

Answer 4

generally, they have an alpha and beta chain

Question 5

in the thymus, what are the 2 rounds of selection that T cells undergo?

Answer 5

positive selection- make sure they respond to MHC complexes

negative selection- make sure they don’t respond to tightly to MHC complexes (autoimmunity)

Question 6

hypervariable regions in the TCR

Answer 6

within the alpha and beta chains, there is a constant region and a variable region. each V region has 3 hypervariable regions, the most important of which is CDR3

these regions are responsible for recognizing antigens and MHC molecules

Question 7

signal 1

Answer 7

this is provided in CD4 t cells by interacting with peptide:MHC2 complexes

provided in CD8 t cells by interacting with peptide:MHC1 complexes

Question 8

signal 2 (costimulations)

Answer 8

provided by APCs via interaction of B7 on the APC and CD28 on the T cell

Question 9

anergy

Answer 9

only receiving signal 1; leads to inactivation

Question 10

describe the formation of immunological synapse

Answer 10

when T cells and APCs meet via MHC/TCR, they release chemokines that recruit and activate integrins on the T cell. the integrins bind to the APC. additional MHCs and TCRs are recruited into this synapse to prolong the interaction

Question 11

describe the importance of IL2 in t cell activation

Answer 11

activated T cells (primarily Cd4) secrete IL2 that acts in paracrine and autocrine fashion to induce clonal proliferation

Question 12

describe the importance of CTLA-4 in t cell suppression

Answer 12

activated t cells begin expressing CTLA-4, which also interacts with B7 on APCs (with higher affinity than CD28). CTLA-4 has an inhibitory effect on t cells and help control t cell activation after the infection has cleared.

Question 13

define superantigen

Answer 13

nonspecifically bind to and activate b-chain on TCRs, leading to polyclonal expansion. subsequent chemokine release leads to uncontrollable immunological cascades that can result in death (ie toxic shock)