How does the immune system respond to a pathogen that the person has been vaccinated against?
2 Answers
The immune system remembers molecules of pathogenic origin once vaccinated, so that in subsequent natural invasions by same pathogen our body can successfully fight to prevent the disease.
Explanation:
During vaccination killed/attenuated germs or their parts or modified toxins are introduced in our body. These foreign molecules are antigenic, hence the body prepares itself to produce antibodies.
For example, a child receives toxoid (modified bacterial toxin which is rendered nonpoisonous) of diphtheria through injection. Many Macrophages and Lymphocytes immediately get exposed to this foreign chemical.
Once exposed, these lymphocytes get programmed to produce antibodies against the particular antigen; in this case against the toxin of diphtheria pathogen. Some of these programmed lymphocytes will remain in the body as memory cells .
When the child is exposed to live diphtheria germs in the environment, memory cells will immediately recognise the pathogen, and start proliferation, to give rise to many more antibody secreting cells .
Antibodies are bullets which deactivate the antigens; specific antibodies work against particular antigen. Due to fast action of antibodies, germs fail to reproduce in the body; they are rather killed quickly before being able to develop any disease symptom .
Vaccination thus helps our body to develop a life long active immunity against diseases.
To learn more, check out this link from the Center for Disease Control or this in-depth link on the human immune system and disease.
Vaccines are based on the ability of the memory cells to remember a pathogen and attack them when they are again attack us.
Explanation:
Once a weak form of a pathogen is inserted into the host (such a form of the pathogen is present in the vaccine), our immune starts forming antibodies against that pathogen or its proteins. This response is stored in the memory of the immune system within the memory B cell.
If the host is subjected to subsequent infection by the same pathogen, the memory B cells recognise the pathogen on the basis of their memory, and produce a huge army of antibodies and T helper cells that help in eradicating the infection caused by the pathogen.
This is the reason that if we suffer from chicken pox once.. we won't suffer ever again. The genome of the virus and the protein it synthesises are recorded by the memory B cells. Any subsequent infection is eradicated and we do not find any symptoms.
