antibodies and the immune system Flashcards
name two types of immunity
innate / nonspecific immunity, present at birth
adaptive / specific immunity, involves memory component
first line of defence
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
name the two main responses for second line of defence
cell intrinsic responses (innate) - cells recognise they have been infected and take measures to kill the invader
1. interferons
2. complement
what are interferons and what is their role?
proteins produced by infected lymphocytes, macrophages and fibroblasts alerting immune system / preventing replication in neighbouring uninfected cells
describe the role of complement
preteins in blood plasma / PM, enhance immune reactions and promotes phagocytosis via cascades
three pathways to activate complement
classical (antibody binding)
lectin
alternative pathway (pathogen surfaces)
to cleave C3 (leading to pore formation and lysis etc)
name some cells that destroy invaders as part of innate defence
phagocytic cells: neutrophils, macrophages
Natural killer cells
two main adaptive immune system responses
cell mediated (T-cells activated to kill virus cells)
antibody mediated (B cells produce antigen-specific antibodies)
define antigen
antibody generator
any substance capable of eliciting an ADAPTIVE immune response
two features of antigens
immunogenicity - can provoke immune response
reactivity - ability to react specifically with provoked antibodies
define lymphocytes
white blood cells that are part of the immune system (ADAPTIVE)
consist of B and T cells
name the primary lymphoid organs
thymus
bone marrow
three types of T cells
Helper T cells (CD4) and Cytotoxic (CD8)
also regulatory (suppressor) T cells, which suppress the activity of other cells
define clonal selection theory
B cells huge diversity, different receptors
lymphocyte encounters antigen, activates + proliferates + differentiates = clonal expansion
also produces memory cells
what are effector cells?
activated cells that produce antibodies against the antigen that activated the B cell
how is immunological self-tolerance developed?
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)
what are antibodies synthesised by?
B cells exclusively
also called immunoglobulins
among the most abundant protein components in blood
antibody general structural features
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
classes of antibodies
IgA
IgD
IgE
IgG - the major class in blood
IgM - the first class of antibody that a developing B cell makes
some roles of antibodies
neutralise antigens
immobilise bacteria
enhance phagocytosis
activate complement
define opsonisation
the process in which antibody or complement coating of a pathogen increases phagocytosis efficiency
how is phagocytosis activated by antibody binding?
antibody coats bacterium
the Fc region on antibody binds with the cell-surface Fc receptors on neutrophils / macrophages, activating the phagocytic process
avidity / affinity define
affinity = strength of binding at sites
avidity = sum of affinities, ie. more binding sites of the same affinity = more avidity
explain how antibodies can respond to many different antigens
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
what is the affinity constant?
Ka, expresses the strength of interaction at antibody-antigen binding domains
Ag+Ab <–> AgAb
Ka = [AgAb] / [Ag][Ab]
what happens at half the maximum binding ?
for Ka = [AgAb] / [Ag][Ab]
Ag+Ab <–> AgAb, so [AgAb] = [Ab]
hence Ka = 1/[Ag]
the affinity constant is equal to the reciprocal al of the antigen concentration
How do T and B cell responses differ ?
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
role of MHC
MHC proteins bind to antigen peptide fragments and carry them to the surface of antigen-presenting cells, where T cells recognise them
how are polyclonal antibodies generated for use in immune therapies?
antigen injected into animal, activating B cells which produce polyclonal antibodies
antiserum obtained from animal
what is a hybridoma?
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
what are humanised antibodies?
antibodies obtained from non-human species with modified sequences
usually applied to monoclonals developed for human drugs
