antibodies and the immune system

Question 1

name two types of immunity

Answer 1

innate / nonspecific immunity, present at birth

adaptive / specific immunity, involves memory component

Question 2

first line of defence

Answer 2

innate immunity: skin (epidermis) and mucous membranes
+ nose hairs, cilia in upper respiratory tract

act as physical and chemical barriers - prevent easy access of microorganisms

Question 3

name the two main responses for second line of defence

Answer 3

cell intrinsic responses (innate) - cells recognise they have been infected and take measures to kill the invader
1. interferons
2. complement

Question 4

what are interferons and what is their role?

Answer 4

proteins produced by infected lymphocytes, macrophages and fibroblasts alerting immune system / preventing replication in neighbouring uninfected cells

Question 5

describe the role of complement

Answer 5

preteins in blood plasma / PM, enhance immune reactions and promotes phagocytosis via cascades

Question 6

three pathways to activate complement

Answer 6

classical (antibody binding)
lectin
alternative pathway (pathogen surfaces)

to cleave C3 (leading to pore formation and lysis etc)

Question 7

name some cells that destroy invaders as part of innate defence

Answer 7

phagocytic cells: neutrophils, macrophages
Natural killer cells

Question 8

two main adaptive immune system responses

Answer 8

cell mediated (T-cells activated to kill virus cells)
antibody mediated (B cells produce antigen-specific antibodies)

Question 9

define antigen

Answer 9

antibody generator
any substance capable of eliciting an ADAPTIVE immune response

Question 10

two features of antigens

Answer 10

immunogenicity - can provoke immune response
reactivity - ability to react specifically with provoked antibodies

Question 11

define lymphocytes

Answer 11

white blood cells that are part of the immune system (ADAPTIVE)
consist of B and T cells

Question 12

name the primary lymphoid organs

Answer 12

thymus
bone marrow

Question 13

three types of T cells

Answer 13

Helper T cells (CD4) and Cytotoxic (CD8)

also regulatory (suppressor) T cells, which suppress the activity of other cells

Question 14

define clonal selection theory

Answer 14

B cells huge diversity, different receptors
lymphocyte encounters antigen, activates + proliferates + differentiates = clonal expansion
also produces memory cells

Question 15

what are effector cells?

Answer 15

activated cells that produce antibodies against the antigen that activated the B cell

Question 16

how is immunological self-tolerance developed?

Answer 16

in primary lymph organs mostly

receptor editing: potentially self-reactive B cell recognises a self antigen and alters antigen receptor

Apoptosis / deletion
Anergy = remains alive but unresponsive (inactivated / repressed)

Question 17

what are antibodies synthesised by?

Answer 17

B cells exclusively
also called immunoglobulins

among the most abundant protein components in blood

Question 18

antibody general structural features

Answer 18

Y shaped
identical antigen binding site at arms (“bivalent”)

two identical light (arms) and heavy chains (base)
each consists of a constant (C terminus) and variable region (N terminus –> diversity of binding sites)

held together by a combination of noncovalent and covalent (disulphide) bonds

Question 19

classes of antibodies

Answer 19

IgA
IgD
IgE
IgG - the major class in blood
IgM - the first class of antibody that a developing B cell makes

Question 20

some roles of antibodies

Answer 20

neutralise antigens
immobilise bacteria
enhance phagocytosis
activate complement

Question 21

define opsonisation

Answer 21

the process in which antibody or complement coating of a pathogen increases phagocytosis efficiency

Question 22

how is phagocytosis activated by antibody binding?

Answer 22

antibody coats bacterium
the Fc region on antibody binds with the cell-surface Fc receptors on neutrophils / macrophages, activating the phagocytic process

Question 23

avidity / affinity define

Answer 23

affinity = strength of binding at sites

avidity = sum of affinities, ie. more binding sites of the same affinity = more avidity

Question 24

explain how antibodies can respond to many different antigens

Answer 24

alternative splicing of coding (exons) and non-coding sequences (introns) in the primary RNA transcripts gives rise to many variations in polypeptide chain of the H/L chains in antibodies

Question 25

what is the affinity constant?

Answer 25

Ka, expresses the strength of interaction at antibody-antigen binding domains
Ag+Ab <–> AgAb

Ka = [AgAb] / [Ag][Ab]

Question 26

what happens at half the maximum binding ?
for Ka = [AgAb] / [Ag][Ab]

Answer 26

Ag+Ab <–> AgAb, so [AgAb] = [Ab]

hence Ka = 1/[Ag]
the affinity constant is equal to the reciprocal al of the antigen concentration

Question 27

How do T and B cell responses differ ?

Answer 27

T cells are activated by foreign antigens only when the antigen is displaced on the surface of antigen-presenting cells
recognises fragments of protein antigens

B cells recognise intact proteins antigens

Question 28

role of MHC

Answer 28

MHC proteins bind to antigen peptide fragments and carry them to the surface of antigen-presenting cells, where T cells recognise them

Question 29

how are polyclonal antibodies generated for use in immune therapies?

Answer 29

antigen injected into animal, activating B cells which produce polyclonal antibodies
antiserum obtained from animal

Question 30

what is a hybridoma?

Answer 30

used to make monoclonal antibodies
made by hybrid cell technology

clone of cells from a. single antibody producing cell + immortalised cell line from B lymphocyte = hybridoma that multiplies indefinitely in cell culture

Question 31

what are humanised antibodies?

Answer 31

antibodies obtained from non-human species with modified sequences

usually applied to monoclonals developed for human drugs