Immunology - Antigens: Triggers Of Acquired Immunity - Ch 7

Front 1

Define antigen

Back 1

Any foreign substance that can bind to specific lymphocyte
receptors can induce an immune response.

Front 2

What are examples of microbial antigens?

Back 2

Bacterial Antigens
Capsule-`K’ antigen
Pili -`F’ antigen
Flagellum-`H’ antigen
Cell wall-`O’ antigen
(Lipopolysaccharide LPS-endotoxin)
Exotoxins

Viral antigens (endogenous- produced inside the cell)

Fungal, Protozoa, Helminth antigens

Front 3

What are examples of nonmicrobial antigens?

Back 3

Food, pollen, snake toxin

Foreign cell-surface antigen
Blood transfusion (RBC)
Graft rejection (MHC antigen)

Autoantigens (autoimmune diseases)
autoantibodies directed against self antigens (hormones, myelin, basement membrane)

Front 4

What are the exogenous and endogenous antigens and how do they respond?

Back 4

1) Extracellular (exogenous)–live outside the cell. Most bacteria, fungi
most protozoa, helminths.
Humoral immune response

2) Intracellular (endogenous)-live inside the cell: Viruses and intracellular bacteria, protozoa.
Cell-mediated immune response.

Front 5

What makes a good and poor antigen?

Back 5

Good antigen:
Foreign protein
Complex carbohydrate
Molecular weight>1000 daltons
Bacterial CpG DNA
Structurally stable antigen
Degree of foreigness
Graft between species

Poor antigen:
Lipids, simple carbohydrate
Mol.wt<1000 d (glucose)
Mammalian DNA
Highly flexible antigen
Self-antigens

Front 6

Define epitope or antigenic determinants

Back 6

A specific region on the surface of an antigen, against which immune responses are directed.

Many epitopes may be present on a large antigen

Some are immunodominant epitope (favorite) than others

Usually about 4-5 amino acids long.

Front 7

Define hapten. How does it relate to penicillin or poison ivy?

Back 7

A small molecule that cannot initiate an immune response unless first bound to an immunologic carrier molecule (usually a protein).

Pencillin degraded to “penicilloyl” (hapten) binds to albumin- develop allergy to drug. Penicillin is usually degraded to penicilloyl, but depending on host genetics, there may or may not be a response.


Poison ivy-resin “urushiol” binds to skin proteins and develops skin rash called allergic contact dermatitis (attacked by lymphocytes).

Front 8

What are cross-reactions? And examples of it along with their implications.

Back 8

Antibodies directed against one antigen may react unexpectedly with an unrelated antigen or react with similar protein in different species.

Antibodies to Yersinia enterocolitica (not harmful) cross-reacts with Brucella abortus in diagnostic test. So Don’t kill the Y.e -infected animal because of false-positive reaction. To confirm yersinia vs brucella you need to run a pcr and add brucella primers to see which it is.

Feline infectious peritonitis virus ab (FIP-cats) cross reacts with transmissible gastroenteritis virus (TGE-pigs). FIP is difficult to grow and TGE is easy to grow, so by detecting antibodies to TGE in cats,-diagnose FIP.
Both diseases are caused by Coronavirus.

Front 9

Why do different blood types auto-immune react?

Back 9

Because they have already reacted to bacteria or food antigens carrying epitopes similar to or identical to the other blood types.

Why don’t type a auto-attack? Because they would recognize epitope A from the bacteria/food antigen as a self-antigen. They’d find another one to use to react to.