Antigen recognition by lymphocytes I

Question 1

what are lymphocytes

Answer 1

A type of immune cell that is made in the bone marrow and is found in the blood and in lymph tissue

Question 2

what are the two types of lymphocytes

Answer 2

B and T

Question 3

what do B lymphocytes make

Answer 3

antibodies

Question 4

what do T lymphocytes do

Answer 4

help kill tumor cells and help control immune responses

Question 5

Coordination of immune response

Answer 5

T cell-independent antigens only produce IgM antibodies in small amounts

Vast majority of antibody responses require T cells to help

All T cells are specific for one antigenic determinant binding of antigen Clonal expansion

Question 6

T cell receptor (TCR)

Answer 6

1. Structure on T cell surface that recognises antigen
2. Structurally related to immunoglobulin Fab region
3. Recognizes antigen in form of a complex offoreign peptide bound to an MHC molecule

Question 7

what is TCR similar to

Answer 7

Fab fragments of an antibody but not identical

Question 8

what bond links alpha and beta chains

Answer 8

disulphide bridges

Question 9

what do the majority of t cells have

Answer 9

αβ TCR

Question 10

Major t cell classes

Answer 10

T cells fall into two major classes, which have different effector functions and are distinguished by the expression of the cell-surface proteins CD4 and CD8

Question 11

on helper t cells TCR is associated with what

Answer 11

CD4 + CD3

Question 12

on cytotoxic t cells TCR is associated with what

Answer 12

CD8+CD3

Question 13

what is required to make an effective response to an antigen

Answer 13

CD4 and CD8

Question 14

what do cd4 and cd8 mediate

Answer 14

additional contacts with MHC molecules

Question 15

cd4 and tcr binding

Answer 15

when cd4 and TCR bind simultaneously to the same MHC class 11: peptide complex, the T cell is about 100x more sensitive to the antigen than if cd4 were absent

Question 16

Summary I

Answer 16

Every lymphocyte is specific for a single antigenic structure

There are many variants (1011) of both B and T cells, each with a uniqueantigen specificity

The receptor for antigen on a B cell (BCR) is a form of the antibody it is programmed to make

The receptor for antigen on a T cell is the T cell receptor (TCR)

Lymphocytes are activated by binding antigen, which triggers them to divide to form a clone of antigen-specific cells

Activated B cells become plasma cells, secreting antibody specific for the antigen

While not identical, TCR is structurally related to immunoglobulin Fab

TCR recognises a combination of MHC plus processed antigen throughthe CDRs of its variable domains

Question 17

summary 2

Answer 17

Helper T cells and cytotoxic T cells are major subsets of T cells

Helper T cells express CD3 & CD4; Cytotoxic T cells express CD3 & CD8

TCR on helper T cells recognises combination of antigenic peptide + MHCClass II on antigen presenting cells (APC)

CD4 also makes contact with MHC class II on antigen presenting cell

Adhesion molecules LFA-1 and ICAM-1 serve as accessory moleculesforming additional adhesive interactions between T cells and APC

Outcome is that APC delivers three kinds of signal to T cell – resulting inactivation, survival and differentiation

After binding antigen, CD4+ T cells secrete cytokines which coordinateimmune response, aiding B cells to make robust antibody response