The effectiveness of antigens

An antibody is made up of two heavy chains and...

Schematic of an antibody molecule: Image via Wikipedia

We introduced the concept of antigens in lecture this past week, and defined them as aspects of a pathogen that induce an immune response. We further carried over the concept of “patterns” that we learned about from innate immunity, describing antigens as patterns with significantly more specificity than molecules like peptidoglycan.  This raises the fascinating question of what makes an effective antigen, and why should we care?

We are already familiar with the most significant aspects of the adaptive immune system:

  1. it is acquired, and not present at birth
  2. it demonstrates increased specificity relative to innate pattern recognition
  3. it demonstrates memory, so that subsequent exposures are faster and more effective than initial exposures to a given antigen.

A “good” antigen therefore would be one that allows a “better” immune response; that it, the host is either able to fight off the infection more rapidly, or even better, not demonstrate any disease symptoms at all. This is the basic principle behind vaccination, where we purposefully expose an individual to an innocuous antigen, and an immune response is generated against that antigen so that when the individual comes into contact with the pathogen that bears that antigen, an adaptive immune response is all ready to protect the individual. A “poor” antigen in this case would be undesirable, as it would not induce an appropriate immune response, and the individual would have no significant protection against the pathogen.

So let’s think about what types of molecules are effective antigens, and how can we increase this from a therapeutic point of view.  We stated in lecture that larger molecules are better antigens than small molecules, and that chemically complex molecules are also better antigens.  We can then evaluate biological molecules for their antigenic effectiveness:

    Biomolecule Basic Component Antigenicity
    Protein Amino acids Excellent
    Carbohydrate Sugars Moderate to poor
    Lipid Fatty acids Very poor
    Nucleic acid Nucleotides Very poor

We also introduced the concept of exogenous, endogenous, and autoantigens in lecture.  Autoantigens are antigens which we find on our own cells, and which our immune systems will delete from the repertoire of potential immune responses during the process of fetal and newborn development. Effectively this means that if a pathogen were to have an antigen that closely resembles one of our own autoantigens, it should be poorly effective at initiating an immune response.

Vaccine development takes all of these things into consideration when trying to decide what will make a “good” antigen, and therefore be effective at providing immunologic protection. The big drawback with most vaccines though is that a vaccine typically is challenging the individual with only a portion of a pathogen, and are less effective than exposure to the whole pathogen. Vaccines will circumvent this difficulty with the administration of adjuvants, compounds that are given with an antigen to increase the effectiveness of the immune response.  It is actually the adjuvants that people generally have adverse reactions to with vaccinations, not to the antigens in the preparation themselves.

BONUS: Using your favorite search engine, identify a vaccine currently in use, and indicate what the antigen (or antigens) are in the vaccine. Because this is a bit more in depth than some others, I declare that this bonus is worth 2 points. Please include your source when you comment!

Advertisements

About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on March 28, 2011, in Bonus!, Important, Lecture. Bookmark the permalink. 6 Comments.

  1. Steph Weakland

    Gardasil is a vaccine aimed to protect against human papillomavirus, or HPV, which can lead to cervical cancer in women and other conditions and cancers in men as well. It contains proteins from HPV Types 6, 11, 16, and 18. Two of these are responsible for about 75% of cervical cancer cases and the other two are responsible for about 90% of genital warts cases.

    http://www.gardasil.com/gardasil-product-information/index.html

    [Note added by Singleton; in fact, Gardasil is soon (or may already be) recommended for men as well as women!]

  2. The meningococcal vaccine protects people from getting meningococcal disease. Meningococcal is a bacterial form of meningitis. This infection has a thin lining that surrounds the brain and spinal cord. It can cause severe brain damange, and in some cases even result in death if not treated. There are two different types of vaccines; polysaccharide vaccine and the conjugate vaccine. They both contain antigen for serogroups A, C, Y and W-135. Serogroups A and W-135 are very rare in the US, but serogroups C and Y accound for about 2/3’s of invasive meningococcal disease in the US.

    http://www.immunize.org/askexperts/experts_men.asp#products

    [Note added by Singleton; Menactra is the trade name of the meningococcal vaccine, which is required for matriculation at YCP for all students.]

  3. The Varicella vaccine is offered to help prevent people from getting Varicella, or Chicken Pox, a common childhood disease which can lead to infections, dehydration, and more severly necrotizing fasciitis aka “flesh-eating bacteria.” Chicken Pox can also affect adults as well, but is more commonly known as Shingles and can be much more severe. The Varicella vaccine is offered in two different forms both of which contain live attenuated viruses. One is offered as a single antigen vaccine (Varivax) and the second is offered as a combo vaccine of measles, mumps, rubella, and varicella (Proquad or MMRV)

    http://www.cdc.gov/vaccines/vpd-vac/varicella/vac-faqs-clinic.htm
    http://www.chop.edu/service/parents-possessing-accessing-communicating-knowledge-about-vaccines/vaccine-preventable-diseases/chicken-pox.html#disease-vaccine-parties

  4. Brittany MacFadden

    Zoster Vaccine (Herpes Zoster Vaccine) (Zostavax) which is for prevention of herpes zoster (shingles) in individuals 60 years of age and older. I’m guessing the name of the antigen is Zostavax? I don’t know what type of suffix or anything in the name to look for to know that it is an antigen…
    http://www.fda.gov/BiologicsBloodVaccines/Vaccines/ApprovedProducts/UCM093833

  5. A Vaccine for the measles virus is the MMR vaccine also known as the measles-mumps-rubella vaccine. It uses a single antigen of the live, or weakened strains of the measles, mumps, and rubella viruses. The virus is to be injected into the subcutaneous layer of the skin, and everyone that does nto have a valid excuse not to get the vaccination should definately get it as soon as possible.

    http://www.vaccineinformation.org/measles/qandavax.asp#top

%d bloggers like this: