Module 2: Antigens and antibodies Flashcards
antigen
a variety of large molecular structures that can interact with an antibody or a t cell receptor
immunogens
antigens that are recognized by a persons immune system as foreign or abnormal and which therefore cause an immune response
Not all antigens are immunogens
tolerogens
antigens for which an individual developed tolerance in contrast to an immunogen which evokes an immune response.
Self antigens are usually tolerated
Allergens
antigens that elicit production of IgE antibodies instead of IgM/IgG of normal immune response
Antigenicity
potency of an antigen
Hapten
chemically active substance with LOW molecular weight that is unable to induce an immune response by itself but when conjugated with a carrier molecule, it becomes immunogenic
heterophile antibodies
endogenous antibodies present in human serum that may interfere with various immunoassays
Heterophile antigens
an antigen common to more than one species
ex. exposure to e coli early in life initiates anti B production in blood group A and O individuals
epitope
epitope of an antigen is the exact structural component either on or within an antigen with which an antibody reacts
AKA antigenic determinant
Carrier region
regions on the antigen structure to which antibody is not formed
Specificity
exact anatomic and molecular characteristics of the epitope that enables it to be recognized and classified
9 factors affecting ability of antigen to evoke an immune response
Chemical nature of antigens (proteins/IgG are best; polysaccharides/IgM less immunogenic; lipids, nucleic acids and inorganic substances not immunogenic)
Chemical complexity
Molecular size
Structural conformation of the molecule
Ionic charge (high charge could decrease immunogenicity)
Foreignness
Route, dosage, frequency of exposure to immunogen
Genetic composition of host (age, health)
Adjuvants
Adjuvants
agents that can be administered with antigen that enhance the immune response
not immunogenic on their own
2 ways antibodies are produced by b lymphocytes and secreted through the exocytosis pathway
Membrane bound
Secreted form
Membrane bound antibody production
antibody serve ad the b cell antigen receipt (site on b cell which will bind with corresponding antigen)
If they make contact with specific antigen, B cell differentiates and becomes an antibody forming plasma cell
Secreted form antibody production
plasma cells secrete free antibody into the blood or lymph
Secreted ab promote phagocytosis, neutralize antigens and activate complement
2 types of light chains
kappa
lambda
5 kinds of heavy chains
differentiate the class of antibody
IgM mu chains IgG gamma chains IgA alpha chains IgD delta chains IgE epsilon chains
domains
loops of about 110 amino acids in the heavy and light chains
constant domains of heavy chains
have the same amino acid sequence for all antibodies in a class
constant domains of light chains
have the same amino acid sequence for either kappa of lambda light chains
Variable domains (VH and VL)
have amino acid sequences that are specific to the epitope of the antigen that induced antibody production
function of variable light domain
determines antibody specificity
site of antigen binding
function of constant light domain
determines if chain is kappa or lambda
orientates antibody during antigen binding
function of variable heavy domain
determines antibody specificity
site of antigen binding
function of constant heavy 1 domain
orientates antibody during antigen binding
function of constant heavy 2 domain
involved in complement activation
function of constant heavy 3 domain
involved in phagocyte binding
Fab (fragment antigen binding) fragment
consists of entire light chain and half of heavy chains
NH2 (amino) end of the antibody
Site that recognizes and binds antigen (epitope)
Fc fragment (fragment crystallizable)
consist of other half of heavy chain
COOH end
Functions: Complement activation
Macrophage attraction when coating an antigen
Placenta expresses Fc receptors; allow binding of maternal IgG molecules for transport across placenta to baby
May be labeled for in vitro detection of antigen
Isotypes
different classes and sub classes of antibodies and are defined by differences in the constant domains of the heavy chains
Allotypes
antibodies that are products of allelic genes
Idiotope
the unique amino acid sequence found in variable region of heavy and light chains of antibody
AKA Complementarity determining region CRD, hypervariable region HVR
Idiotype
the sum of the unique amino acid sequences found in the variable domain of the H and L chains of an antibody at or near the antigen binding site
About IgG
Heavy chains: 2 gamma chains (monomer)
Crosses placenta? yes
Function: opsonization, complement activation, neonatal immunity
Isotypes: IgG1, IgG2, IgG3, IgG4
Binds complement? yes, esp. IgG1 and IgG3
About IgM
Heavy chains: 10 mu chains (pentamer)
Function: 1st antibody produced by newborn, activates complement, acts as naive b cell antigen receptor
Binds complement? yes
About IgE
Heavy chains: 2 epsilon chains (monomer)
Function: immediate hypersensitivity, parasitic infections
Binds complement? no
About IgA (serum)
Heavy chains: 2 alpha chains (monomer)
Function: mucosal immunity, found in colostrum
Isotypes: IgA1, IgA2
About IgA (secreted)
Heavy chains: 4 alpha chains (dimer)
Function: mucosal immunity
Isotypes: IgA1, IgA2
About IgD
Heavy chains: 2 delta chains (monomer)
Function: Naive b cell antigen receptor, increased in some auto-immune diseases
IgA makes up about __% of the antibody we produce everyday and is produced in the _____________
70%
mucosal lymphoid tissue
IgA use in the body
transported through epithelial cells to the lumen of the GI or resp tracts
Secreted IgA recognizes antigen and binds to it, preventing it from adhering and entering through the epithelium
also, Opsonization leads to phagocytosis
The first line of defence against bacteria and viruses is
secretory IgA
Secretory component helps antibody resist breakdown by proteolytic enzymes of the GI tract
what is a babys immunity before they produce IgG themselves
IgG from mom through placenta After birth, IgA in maternal milk First 6 months: maternal IgG levels decline as baby begins their own immunoglobulin synthesis IgM starts 3 months before birth IgG starts 3-6wks after birth
Meconium
dark green mucilaginous substance of the intestine in full term infant
Consists of intestinal gland secretions and some amniotic fluid (contains IgG)
Colostrum
thin milky fluid of the mammary gland produced a few days before and after parturition (contains IgA)
Polyclonal response
many different antibodies derived from B cells which have recognized different epitopes on the antigen
Normal B cell immune response to and antigen is polyclonal
Monoclonal antibodies
antibodies derived from a single B cell clone, and that only recognize only one epitope of an antigen
Polyclonal antibody production facts
Mixture of various B cell clones inexpensive Short process to make Produces large amounts of non-specific Ab Recognizes many epitopes on antigen Batch to batch variability
Monoclonal antibody production facts
Single types of B cell clone Expensive Long process to make Produces large amounts of specific Ab Only recognizes one epitope No batch to batch variability
