5.3: Humoral (Antibody Mediated) Immunity Flashcards
(18 cards)
Antibodies (Ab) are also called _
Immunoglobulins (Ig)
what are Antibodies (Ab) made up of?
- Glycoproteins composed of 4 subunits
-2 identical heavy chains (inner and stems)
-2 identical light chains (outer upper part) - Each antibody has 2 identical antigen binding sites (Fab)
- and one Fc site (constant fragment) - binding site that interacts with other components of the immune system
what is the Fab part of the antibody
the 2 identical binding sites, (think a and b in fab for antigen binding)
fab=fraction of the antibody
what is the Fc site on the antibody
the part of that can interact with other components of the immune system.
(think c in Fc is for components)
Fc =constant fragment
what are the 5 classes of antibodies
- Immunoglobulin G (IgG)
- IgA
- IgM
- IgE
- IgD
(remember by word big letters make: GAMED)
describe Immunoglobin G (IgG) antibodies
- A monomer (one Y-shaped antibody)
- Most abundant antibody in blood and tissues
- Most important for combating a pathogen
describe IgM antibodies
- A pentamer (5 Y-shaped antibodies)
- first antibody made when a new antigen is encountered
- excellent at agglutination -sticking things together (bc it has 10 identical antigen binding sites, could combine a bunch of antigens and antibodies together)
- does not leave blood and enter tissues
describe the IgA antibodies
- A dimer (2 antibodies linked with a (J) chain protein)
- secreted into saliva, tears, mucous
- helps to protect mucousal surfaces (protects us from invaders that have tried to cross mucous membranes before)
- important defense against respiratory, reproductive, and digestive tract infections
describe the IgD antibodies
- Monomer
- Aka B cell receptors: found on surface of B cells
- Plays a role in activating B cells to respond against an antigen
describe the IgE antibodies
- Monomer
- found on the surface of mast cells and basophils
- causes them to release granules of histamine
-triggers allergic response
(overactive mast cells react against harmless things (causing allergies))
what are the 5 protective functions of antibodies
- Neutralization
- Opsonization
- Agglutination
- Antibody mediated cytotoxicity
- Complement activation
describe the Neutralization protective function of antibodies
- Ab stick to antigens on a foreign particle and block attachment sites (covered in antibodies = neutralized)
-stops bacteria, viruses and toxins from entering host cells (bc it makes them too large to enter the cell)
describe the Opsonization protective function of antibodies
- Ab stick to a pathogen’s surface and flag down phagocytes (makes them more likely to be recognized by macrophages)
- Phagocyte interacts with the Fc region and engulfs the pathogen
- Greatly increases rate of phagocytosis
describe the Agglutination protective function of antibodies
- Ab can stick to two identical antigens at once (so a pentamer for ex. can attach to 10 antigens at once, 10 binding sites)
- Bridges particles together in clumps
- so they can be phagocytized more easily
describe the Antibody mediated cytotoxicity protective function of antibodies
- Ab binds to antigen on the surface of a parasite (too large to be engulfed by phagocytosis)
- Fc can interact with eosinophils
- Eosinophils release enzymes and reactive oxygen intermediates to attack the parasite
describe the Complement activation protective function of antibodies
- Ab bound to a bacterial cell can activate complement
-a set of proteins in the blood that assist other components of the immune system
-“classical pathway” of complement activation - Results in the membrane attack complex (MAC)
-Inserts into bacterial membranes
-forms a pore (pokes holes in the cell)
-cell leaks and dies
describe the complement system
Consists of ~30 proteins that circulate in the blood and work together in a “cascade”
* when bacterial cell invades, one protein activates the next protein and so on
* involved in both innate and adaptive immunity
* “Complement” other parts of the immune system
that’s why it’s called that
what are the 3 major functions of the complement cascade and describe them
-
Membrane attack complex (MAC)
-complement proteins poke holes in gram negative bacteria
-gram positives protected by thick peptidoglycan - **Opsonization **
-complement proteins bind to antibodies already attached to antigens, and make the antigen even more likely to be phagocytized -
Enhanced Inflammation
-activated complement proteins can trigger inflammation in response to bacterial infection
-attracts phagocytes to the affected area
