Theme 5a Antigens Flashcards
What is an antigen?
A molecule which interacts with either a BCR (antibody), or a TCR/MHC complex
What is an epitope?
The part of an antigen which recognized by the binding sites of TCR/MHC complex or BCR.
What is a hapten?
A antigen which can only cause an immune response when coupled with a carrier molecule.
What is a superantigen?
It is a molecule which stimulates a strong immune response by binding outside of the specific BCR or TCR/MHC complex binding sites. (not an antigen)
How can penicillin induce thrombocytopenia?
The penicillin drug acts as a hapten and binds to platelets (carriers). Antibodies then bind to platelets and stimulate complement-mediated destruction. This leads to low platelets levels (thrombocytopenia)
Explain the concept of addiction vaccines.
Many drugs like cocaine and nicotine are very small, which allows them to easily pass into the brain without being detected by the immune system. If these drugs were conjugated with bacterially derived carrier molecules then antibodies would have a better chance of detecting the drug and making antibodies specifically for it, allowing them to clear the drug before it can make it to the brain and cause the addictive effect.
Why are superantigens so dangerous?
Because they can cause a nonspecific response in many B / T cells rather than a single clone. For instance some bacteria which enter the body release harmful toxins that can activate up to 20% of all T-cells, initiating a cytokine storm which leads to toxic shock syndrome and multiorgan failure.
Are immune responses to foreign sources always good? are immune responses to self sources always bad?
No to both. You do not want an immune response against your gut microbiome or fetus when pregnant. However, you do want an immune response against cancers.
Why are insoluble antigens more likely to cause a strong immune response than small soluble molecules?
What is the ideal size of immunogens? Why is this so?
Because they are more likely to be detected, phagocytosed and processed by macrophages.
~100,000 daltons because smaller molecules would be hard to present on MHCs.
What factors influence immunogenicity?
- Host genetics (MHC alleles)
- Dose (may cause immune tolerance if too high or low)
- Route of administration (subcutaneous, intravenous, intramuscular, oral, or intranasal)
What is the purpose of adjuvants and how do they work?
They help improve the immunogenicity of an antigen.
- Interact with PRRs or within cells
- Provide physical protection to antigens, prolonging delivery
- induce greater release of danger signals by chemokine releasing cells.
- Help translocate antigens to lymph nodes where T and B cells can more readily recognize them.
