19 - specific immune response

Question 1

what is an antigen?

Answer 1

a molecule that induces a specific immune response

Question 2

what are the 2 arms of specific immunity?

Answer 2

humoural

cell-mediated

Question 3

humoural specific immunity

Answer 3

transferred with serum

directed against ‘free antigens’

mediated by antibodies secreted by B lymphocytes

Question 4

cell-mediated specific immunity

Answer 4

transferred by cells

directed against cell-associated antigens - intracellular pathogens
• intracellular pathogens are not free-floating
• we need a cell-mediated response to deal with them

mediated by T lymphocytes

Question 5

what is humoural specific immunity mediated by?

Answer 5

antibodies (Ig)
• bind to epitopes on Ag
• can act alone
• can act as adaptors

Question 6

what does the immune response used depend on?

Answer 6

• organism
• environment
• status of individual
• delivery of organism

Question 7

what is cell-mediated specific immunity mediated by?

Answer 7

T lymphocytes
• recognise epitopes presented on MHC molecules
• CD8+ - cytotoxic T cells
• CD4+ - T helper cells

Question 8

T cell sub-sets

Answer 8

classified based on surface markers/function:
• T helper cells 
• cytotoxic T cells 
• T regulatory cells 
• memory T cells 
• NKT cells

Question 9

how do antibodies increase inflammation by innate responses?

Answer 9

IgE
• mast cell degranulation
• histamine

IgM and IgG
• complement activation
• C3a and C5a - inflammatory mediators

Question 10

how do T cells increase inflammation by innate responses?

Answer 10

produce inflammatory cytokines

eg. TNF-alpha

Question 11

what are the 2 states of lymphocytes?

Answer 11

normal small lymphocytes
• resting

large lymphocytes
• active

Question 12

normal small lymphocytes (resting)

Answer 12

pale blue cytoplasm and dense, dark stained nucleus

size of nucleus is approximately the same as a normal RBC

16-46% in a normal adult blood smear
• increased in disease

Question 13

large lymphocytes (active)

Answer 13

larger cell with more abundant and granular cytoplasm

a small lymphocyte, B cell or T cell, becomes a large lymphocyte as it is stimulated to proliferate

such a cell can be shown to be able to incorporate tritiated thymidine, a marker of active DNA synthesis

Question 14

what are the 2 stages of differentiation by T and B lymphocytes undergo?

Answer 14

1) differentiate from pluripotent stem cells in bone marrow
2) undergo further differentiation in response to antigen

therefore a specific response is an adaptive response

Question 15

what happens after differentiation?

Answer 15

proliferation - clonal selection

Question 16

features of specific immunity

Answer 16

clonally distributed receptors

low frequency of cells specific for any Ag

response takes time to develop

Ag induces effector and memory lymphocyte formation

Question 17

immunological memory

Answer 17

on subsequent encounters with the antigen a secondary response occurs

due to memory B and T cells - an expanded population specific for antigen

Question 18

B lymphocyte antigen receptors

Answer 18

B cell receptor (BCR/sIg), surface anchored Ig binds free antigen

Question 19

T lymphocyte antigen receptors

Answer 19

T cell receptor (TCR)

binds complex of antigenic peptide plus MHC - T cells can only recognise proteins

T cells express a TCR which always remains anchored to the cell surface

Question 20

clonal selection

Answer 20

1) removal of potentially self-reactive immature lymphocytes by clonal deletion
2) pool of mature naive lymphocytes
3) proliferation and differentiation of activated specific lymphocytes to form a clone of effector cells

Question 21

principle of antibody production

Answer 21

each resting B cell is specific to 1 antigen

contact with antigen activates B cell which divides

differentiates into plasma cells secreting antibody with same specificity as sIg

Question 22

what is bone marrow?

Answer 22

soft spongey, highly cellular tissue that fills the internal cavity of bones

Question 23

what is the thymus?

Answer 23

vascular tissue

only 2-3% of T cells produced actually make it - inefficient but need to get rid of them so they don’t react

Question 24

secondary (peripheral) lymphoid tissues

Answer 24

lymph nodes, spleen, mucosal associated lymph tissue (MALTs), blood, lymphatics

lymphocytes recirculate and if they meet antigen, undergo clonal expansion and differentiation

immune responses occur in the secondary lymphoid tissues

Question 25

basic structure of a lymph node

Answer 25

inner = medulla 
middle = paracortex
outer = cortex 

they have a good blood supply - need to be able to bring the antigen in but also bring the cells in once they develop in bone marrow and thymus

Question 26

structure of the spleen

Answer 26

a spongey soft organ about the size of a persons fist

located in the upper left part of the abdomen, just under the rib cage

consists of white pulp (mainly lymphocytes) that functions similar to the nodules of the lymph nodes

red pulp contains mainly RBCs and macrophages - main function is to phagocytose old RBCs

Question 27

mucosa associated lymphoid tissue (MALT)

Answer 27

non-encapsulated submucosal lymphoid nodules and diffuse lymphocytic infiltrates in the submucosa of the intestinal and respiratory tracts

gut-associated lymphoid tissue (GALT)

bronchus-associated lymphoid tissue (BALT)