lecture 6 Flashcards
adaptive immune system is optimized to recognize
microbial macromolecules
best antigens are
large, complex, stable, foreign proteins
small molecules of less than 5000Da
are usually poor antigens
small molecules may be made antigenic by linking them to
large proteins (carrier)
small molecules are haptens
haptens
small molecules used as antigen carriers/antigenic - carrying small molecules by linking together
epitopes
specific areas on the surface of foreign molecules that cells of adaptive immune system can use BCR/TCR to recognize
five classes of immunoglobulins
IgG, IgM, IgA, IgE and IgD
all originate as B cell antigen receptors (BCRs) that are shed/secreted into body fluids
IgG
predominant immunoglobulin serum
mainly responsible for systemic defense
blood, tissue, colostrom (predominant Ig) (13.5 mg/mL in serum)
memory responses!
opsonization (binds pathogens and toxins to host cells!)
complement activation
antibody dependent cellular cytotoxicity (ADCC)
neonatal immunity
binds phagocytes vie Fc receptors
secondary/memory responses
2 binding sites
IgM
large immunoglobulin
mainly produced during primary immune response
blood only (1.5 mg/mL in serum) first response to antigen aggregates microbes and large antigens complement activation part of naive B cell antigen receptor
pentameric w J chain
10 binding sites
IgA
produced on body surfaces
responsible for defense of intestinal & respiratory tract
blood, milk, mucosal surfaces (tears, saliva, gut, lungs) (3.5 mg/mL in serum)
prevent entry of pathogens
mucosal immunity
monomeric form in serum
dimeric form has 4 binding sites
IgE
small quantities in serum
responsible for immunity to parasitic worms & allergies
blood and tissues (0.05 mg/mL in serum)
defend against helminthic/ectoparasites
allergy responses/immediate hypersensitivity
IgE + antigen complex activates mast cells and basophils to release vasoactive substances (histamine and serotonin)
2 binding sites
IgD
found on surface of immature lymphocytes
part of BCR
antigen
part of a pathgen/foreign molecule that is recognized by the immune system
antigen recognition
soluble molecules (antibodies) receptors for antigens are on B and T cells, these are antibodies
immunogen
substance that induces immune response when injected into a host
affinity
binding strength of an antibody for antigen
avidity
accumulated strength of multiple affinities of individual binding interactions
direct binding
antibodies recognize/bind exogenous antigens
resting b cell w Ig receptor -> encounter w antigen and binds -> stimulates B cell gives rise to antibody secreting plasma cells for beating out pathogen
indirect binding
T cells recognize endogenous antigens using TCR
A. phagocytes w ingested microbes in vesicles (CD4+ effector T cells -> microbe) -> cytokine secretion -> a. Macrophage activation - killing of ingested microbes b. inflammation
B. infected cell w microbes in cytoplasm (bind to CD8+ T cells) -> kill infected cell!
heteroantigen
foreign to body infectious agent (living or dead) environmental antigens pollens chemicals/drugs
alloantigen
tissues or cells from a genetically dissimilar member of same species
xenoantigen
tissues derived from a differnet species
autoantigen
self or hosts own tissue
foreign
not self or related
molecular size
at least >1000 Da or 1kDa
best immunogens are 100kDa or bigger
complexity
complex glycoproteins w tertiary structure
not simple repeating polysaccharides, lipids or nucleic acids
strutural stability
not easily degraded (toxins) but not inert (plastics, silicon implants, tattoo dyes)
BEST ANTIGENS ARE
FOREIGN, COMPLEX AND LARGE
properties of antigens that detemine potency
foreign, large (>1kDa), complex, stable, route of administration, amount of antigen, host genetic makeup
epitope
discrete site on antigen
recognized by antibodies (host) or T cell receptors)
may involve elements of the primary, secondary, tertiary or quaternary structure
also called antigenic determinants
antibody and t cell receptors recognize different epitopes on
the same antigen
viral antigens examples
Rabies virus’s immunodominant antigen
G glycoprotein spikes -> 400kDa has 16kDa immunodominant epitope
bacterial antigens example
Pilli (F antigens) capsule (K) cell wall (O) flagellum (H) gram negative -> LPS gram positive has more peptidoglycan
haptens
small antigenic molecules that can bind to antibody but are NOT immunogenic
dont elicit immune responses unless BOUND to a carrier protein
ex: drugs, hormones, toxins (too small)
penicillin + albumin (carrier)
major autoantigens of host cells
blood group antigens (erythrocytes)
major histocompatility complex
cluster of differentiation molecules (CD)
MHC
expressed by all nucleated cells
imprtant for tissue recognition, transplantation medicine, antigen processing and presenting in adaptive immunity
cluster of differnetiation molecules (CD)
molecules of biological function that define cell subsets
indentified by monoclonal antibodies
immunoglobulin structure
antigen binding site w variable domains
hinge region
light chain
heavy chain
biological effector functions of antibodies
mediated by the binding of the Fc region (tail/heavy chain):
- Fc receptors expressed by phagocytes, NK cells, Mast cells
- plasma proteins -> complement proteins
IgY
immunoglobulin found in yolk
bird version of IgG (memory responses)
antibodies can bind in
linear or conformational epitopes (folded
multivalent antigens
w different epitopes - requires all different antibodies
w same epitope and antibody
antibodies are flexible due to
hinge region of strucutre
can be widely or closesly spaced
