L8 - Adaptive Immunity Triggers

Antigens

Foreign macromolecules → trigger adaptive immunity

Antigenicity

Molecule’s capacity to be recognized by the immune system

Adaptive immune system can ____ and _____ to almost all the foreign macromolecules present in an invading microbe.

Recognize and Respond

Describe viral antigens

Nucelic acid core with outer protein layer (“capsid”)

Viral proteins expressed on surface of infected cells can induce adaptive immunity

____ proteins are good antigens.

Capsid

Examples of non-microbial antigens

• Food

• Pollen Grains

• Blood Antigens

• Tissue Graft

• Autoantigens

Components of Good Antigens

• Large

• Complex

• Foreign

• Moderate stability

What causes an antigen to elicit an immune response?

1. Route of Administration

2. Amount of antigen administered

3. Genetics of patient

< _____ daltons = poor antigens

1,000

Foreignness of Antigen and Immune Response

Bigger difference between foreign antigen and animal’s own antigens → bigger immune response

Complex molecules and immune response

More complex = bigger molecular weight = more antigenic

(except if they’re repeats of the same polymer)

What make the best antigens?

Proteins

Polysaccharides as antigens

• Most aren’t → broken too quickly

• Can be antigenic when combined with proteins

  • Glycoproteins can cause antibodies to target polysaccharide part of molecule

Autoantigens

Non-microbial antigen

Immune respones against normal body components → autoimmune responses

Do animals recognize self-proteins? Why/why not?

No, B and T cells with self-proteins are eliminated

Why are flexible molecules (flagellin, gelatin etc.) poor antigens? How can they become better?

BCRs and antibodies can’t recognize unstable molecules that change conformation

Stabilization through cross-linking → increases antigenicity

What happens when antigens are broken down too quickly by enzymes?

Not very antigenic → too little time for BCRs to recognize them and present to APC

Why are simple polysaccharides poor antigens?

Too quickly digested

How does an antigen illicit an immune response? What molecules cannot do this?

• Must be degraded by APCs

• Plastics/Stainless steel (inert) → not antigenic and can’t be broken down and presented to TCR

How can polysaccharides, lipids and nucleic acids become more antigenic?

Complex with proteins → less quickly broken down

What elicits an immune response against the polysaccharide portion of the molecule?

Glycoproteins

Epitope

Specific regions on cells of the adaptive immune system where the immune responses occur

Immunodominant epitopes

The most immunogenic epitopes

There is ___ epitope per 5 kDa of protein

one

Haptens

Small molecules that would not illicit an immune response on their own, but will when bound to another larger molecule (“carrier” = protein)

Penicillin Allergy

Penicillin on own shouldn’t illicit immune response

But in those with an allergy, it combines with albumin → becomes antigenic and causes issues

(Hapten = penicillin, carrier = albumin)

Poison Ivy Allergy

Toxic component = urushiol → binds to skin protein → treated as foreign and attacked by lymphocytes

Allergic conctact dermatitis

Cross-reactivity of antigens

• Antibodies can be directed between unrelated antigens (ex. Yersinia antibodies react to Brucella as well)