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Chapter 18: Practical Applications of Immunology
Introduction
So today we're going to talk about Chapter 18 , and Chapter 18 covers the practical applications of immunology. We’re going to talk about: Vaccines – the process and the different types A few diagnostic tests you're likely to see when you're out in practice
Vaccines
We’ve talked a little bit about the history of vaccines already. You know that Edward Jenner was the one that noticed when milkmaids were working and exposed to cowpox , they seemed to develop a very mild disease. But when smallpox came around and they were exposed to that, they did not develop signs or symptoms —they seemed to be immune to it. The word vaccine actually comes from Edward Jenner's work. The word vaca comes from cows , and thanks to his work, we have the scientific documentation and process of developing vaccines.
Vaccination vs Vaccine
Vaccination is the process of deliberately exposing people or animals to harmless versions of the pathogen , in an effort to stimulate their immune system to produce further protection. The vaccine is the actual entity or suspension of the organism or some toxin that is used to induce immunity in the person. So, the vaccine is what’s given, and vaccination is the name of the process.
Effectiveness of Vaccines
There’s lots of documentation illustrating the effectiveness of vaccines. A chart with data up to 2010 shows that before the measles vaccine was widely administered in the early 1960s, there were about 100,000 measles cases per year in the U.S. After the vaccine, you see a significant drop , and as of 1995–2000 , measles cases became almost undetectable —all due to the vaccine.
Controversies & Public Concern
There is some concern that vaccines can lead to various diseases. For a while, there was concern that the polio vaccine caused autism.
Many studies have discounted this and found no correlation. I’m not here to convince you whether you should or shouldn’t get vaccines—merely to explain the science behind them so you can make your own informed decisions.
COVID-19 Vaccine
There’s a lot of talk right now about the COVID-19 vaccine. A lot of people are working to develop this in a very short amount of time. There are complications, and a lot of FDA regulations that are in place for a reason. Again, I’ll explain the science , and you can make your own assertion about whether you want to get the vaccine or not.
Types of Vaccines
1. Live Attenuated Whole Agent Vaccine
Produces the strongest immunity —typically lifetime immunity Uses live pathogens that can replicate but do not cause disease Closely mimics a real infection Activates both cellular and humoral immunity Example : MMR (Measles, Mumps, Rubella)
2. Inactivated Whole Agent Vaccine
Safer than live vaccines Uses dead or completely inactive pathogens Cannot replicate, are not living Often require boosters Only activate humoral immunity—no T-cell memory or cytotoxic T-cell activation
3. Subunit Vaccines
Built using fragments of antigens Expose the body to antigen , not the whole pathogen Cannot replicate or cause symptoms Also called recombinant vaccines
4. Toxoid Vaccines
For pathogens where the toxin , not the microbe itself, causes disease Help produce antibodies that neutralize toxins
Hybridoma = combination of spleen cells from a mouse and cancerous myeloma cells Steps:
- Identify desired antigen
- Inject antigen into a mouse
- After immune response, harvest spleen
- Combine spleen cells with myeloma cells
- These now produce monoclonal antibodies Common Use : Pregnancy tests – use monoclonal antibodies and color change for detection
Serological Tests
Tests that look for antigens or antibodies in body fluids (serum, sputum, etc.)
Types
Direct Test : Looking for the microbe itself Indirect Test : Looking for antibodies (has the person been exposed?) Viruses are mostly detected using indirect tests.
1. Agglutination Test
Antigen-antibody interaction causes visible clumping Advantages : o Sensitive and specific o Easy to read o Can be direct or indirect Example : Blood typing Limitation (Indirect Test) : Cannot distinguish between current infection , past infection , or vaccination You can measure titer (concentration of antibodies) IgM vs IgG IgM high = new infection IgG high = old infection or vaccination
2. ELISA (Enzyme-Linked ImmunoSorbent Assay)
You will have:
A lab activity A Lobster simulation Animations for practice Types: Direct ELISA : Detects the antigen (organism) in the serum o Antibody is bound to a plastic well o Patient serum added o If antigen present → binds → secondary antibody with chromogen → color change o More antigen = darker color Indirect ELISA : Detects the antibodies (exposure history) o Antigen is bound to the well o Patient serum added o If antibodies present → bind to antigen → chromogen-labeled secondary antibody added → color change o More antibodies = darker color
Conclusion
There are many things in this chapter not covered in this lecture. Focus on: What was presented here Study guide material Assigned lab activities and simulations
