Antibodies and vaccines

First of all, its been a long time since I have posted anything. I was very busy with my first semester so could not write anything.

We are going to talk about how vaccines work! For that, we need to know what vaccines are first of all. Vaccines are actually a way of introducing an enemy to your immune system. It’s like we secretly tell out immune cells that if this pathogen ever invades and tries to attack you, kill it right away. All these pathogens are unique and what makes them unique are the “antigens” which are the proteins present on the pathogens. When we introduce these antigens into the body, our immune cells recognise them and produce “antibodies” against them. So when this pathogen tries to invade again, we already have antibodies that will recognise and directly kill them off.

You might be wondering if we introduce the antigens of the pathogen, would it not infect us and what if our immune cells can’t fight it and we end up getting sick? Is that not a risk? Well, not exactly because we always introduce the antigen in a form where it is so weak that it can only raise an alarm in the immune system that ‘hey someone is here’ but doesnt really have the capacity to cause damage.

There are a lot of different types of vaccines used for different purposes:

Live attenuated Inactivated Conjugate
Weak or asymptomatic form
of bacteria or virus
Dead cells of the pathogen are introduced
into the body
A specific part of the pathogen
like a protein or a carbohydrate
from is injected into the body
Too weak to cause an infection and
gives chance to immune cells to recognise it
Immune cells can recognise the antigensImmune cells can recognise the antigen and learn to fight it
Lifelong immunity with one- two doses Vaccines can be freeze dried and stored for long term useLower chance of an adverse reaction

There are some disadvantages of these vaccines as well. The live attenuated vaccines cannot be given to people with a weakened immune system as we would be injecting the whole pathogen. The inactivated vaccine might not have a robust response as the pathogen is activated and hence the immune system is not getting the complete real stimulation. As far as the conjugate vaccines are concerned, identifying the specific proteins of the pathogen that can illicit a response is not possible always.

The Immune System: Immunization (MCAT 2018: Biology) Flashcards ...
Fig 1: representation of an antibody recognising the epitope of an antigen on a pathogen. Acquired form:

Now that we know about the vaccines and pathogens, lets see how the antibodies work in recognising the antigens. This might be a little too detailed but you’ll realise how complicated our immune system actually is.

Structure of Antibody
Fig 2: A simplified version of an antibody representing the different regions in an antibody. Acquired from:
Antibody- Structure, Classes and Functions
Fig 3: A typical structure of an antibody. Acquired from:

As we can see in figure 2, there are 2 main regions of an antibody: the region that remains constant (constant region) and the region that varies according to the type of pathogen (variable region). Each antibody is made up of a unique set of a heavy chain and a light chain.

Classes/Types of Antibody
Fig 4: an image representing details about the five different type of antibodies. Acquired from:

As we can see there are five different types of antibodies also called immunoglobulins (Ig) G A,M,D and E. There are their functions:

long term (months and years) and general protection against pathogens and also triggers complement protein system Binds before antigens invade tissues and keeps the antigens in secretions for easy recognition when it infects againInvolved in ABO blood group antigens on RBC surface and enhances phagocytosis Present in the surface of B cells and plays a role in production of antibodies Binds to mast cells and basophils to promote release of granules to kill the pathogen and may be involved in parasite killing

As we can see, these various antibodies have different functions and they are so important in recognising the antigens and remembering them!

Differences between Primary and Secondary Immune Response
Fig 5: image represents the phases of the IgM and IgG

As we can see, if the antigen is a new enemy, IgM is triggered first and after about 4-5 days, IgG is triggered, whereas if the same antigen comes in again, the IgG shoots up and kills it off as it has the immunologic memory of that particular antigen. As observed in figure 5, the secondary response is much more stronger than the primary response. This is what vaccines do as well so when the same antigen enters, the body is sensitised to it already and thus, the IgG kills it off!

I hope you enjoyed reading this blog! Hail the immune system!


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