Defence Systems & Vaccination

Non-specific defence system

Pathogens present around us are constantly attacking our body and our immunity system is constantly on a war against these pathogens. But, the immunity system only protects us when pathogens have already entered. This makes it necessary to have the first line of defence against these pathogens. This defence is termed as a nonspecific defence system. It can be of two types of barriers against these pathogens:

  • Physical
  • Chemical

Nose

Ever wondered why we sometimes sneeze when we are cooking?

Its because the small particles of the spices enter out the nose and in reaction, our body tries to throw it out.

The internal hairs in the nose act as a physical barrier to the outer dust and thus prevent infection. The nose cells have glands that produce mucus. The mucus helps in trapping the pathogens before they enter the lungs through the air.

Mucus is blown out by us and with it is removed the pathogens that are trapped in it.

Skin

Skin is the main barrier in our body and covers all parts of the body. Even when a cut or bruise occurs on our skin, our body is constantly working to repair it and form a scab that works like a band-aid. Some parts of our body are not covered by skin which is why they have developed their own mechanism to deal with the pathogens and prevent infection.

Example – Tear glands in our eyes produce tears which comprise of enzymes that work as a chemical barrier and kill most of the pathogens entering through eyes.

Trachea and bronchi

The nose is extended to the trachea which is further extended towards the lungs. There are small fibrous hair-like structures called cilia are present in the trachea. These hair-like structures are much smaller than the hairs present in the nose. The cilia present in the trachea moves in a wavy motion and pushes the mucus and pathogens in an upward direction to push it towards the throat where it enters the food pipe and goes into the stomach. The cells that are involved in the formation of mucus are called goblet cells. This mucus act as a physical barrier in airways.

The nose is extended to the trachea which is further extended towards the lungs. There are small fibrous hair-like structures called cilia are present in the trachea. These hair-like structures are much smaller than the hairs present in the nose. The cilia present in the trachea moves in a wavy motion and pushes the mucus and pathogens in an upward direction to push it towards the throat where it enters the food pipe and goes into the stomach. The cells that are involved in the formation of mucus are called goblet cells. This mucus act as a physical barrier in airways.

Stomach

The stomach produces hydrochloric chloric acid, and its function is to make the food acidic and kill the pathogens that come with the food. Its acid is strong, but it still does not harm our stomach because of the lining of the mucus present in our stomach. The acid kills the pathogens but cannot damage our stomach. Thus, the acid work like a chemical barrier in our body.

The immune system against diseases

Now, when a pathogen manages to break the first line of defence as we discussed above, they can cause infections. However, the body does not give up so easily and prepares for the second line of defence. The purpose is to minimize the damage and stop the pathogen from further damaging the body systems. This is known as the immune system. There are two types of white blood cells that are involved in this process:

  • Phagocytes
  • Lymphocytes

Phagocytes

  • These are white blood cells that attack pathogen by attaching to them. Once the pathogen has been attached, the pathogen is surrounded by pathogen and then engulfed.
  • The enzymes present in the phagocyte starts eating the pathogen and kill it.
  • Phagocytes do not have any specific target. They attack all the pathogens that invade our body. Hence, these are non-specific defence systems in our body.

Lymphocytes

  • These are also white blood cells but they are different from phagocytes because they can identify specific targets. They have the ability to recognise the pathogens by identifying the proteins present on their surface called antigen. The antigen of the pathogens is recognised as foreign and this stimulates the lymphocytes to produce the defence in the form of antibodies.

  • The process takes time (a few days) and the person might also feel sick. The antibodies spread throughout the blood vessels and get attached to the pathogen. This restricts their movement and makes it easier for phagocyte to engulf and then kill them.
  • The toxins produced by pathogens make you feel sick. Antitoxins are produced by lymphocytes to neutralise the effect of toxins by preventing them to bind on to the cells of the body.
  • Antibodies and antitoxins produced by lymphocytes work in a target-specific manner. Therefore the system of lymphocyte protection is called specific

Vaccinations

Diseases are caused by microorganisms called pathogens. Vaccines consist of a dead or attenuated form of a pathogen for a specific disease. A specific antigen is present in the pathogen which is recognized by the lymphocytes of our immune system. In response, the antibodies are produced, that target the pathogenic antigen.

Working of Vaccination

  • The attenuated pathogen is unable to cause any major harm is introduced in our body.
  • Lymphocytes respond to these invaders and release complementary antibodies that target the specific antigen which was introduced in our body.
  • The antibodies get attached to these antigens and form a clump.
  • Now, phagocytes come in action and envelop the antigens and start acting on the clump through enzymes leading to its degradation.
  • After the first encounter of specific antigens, the memory is developed for these antigens as some lymphocytes now remain in bloodstreams and can again form the antibody if the pathogen again attacks the body.
  • When a pathogen infects the body next time and not in attenuated form, the memory cells instruct the lymphocytes to release antigens even more quickly than before and kills it in way less time than before.

Types of the immune response

Primary immune response:

  • When the pathogens infect the body for the first time, the response of the immune system is slow, and there is a slow and gradual increase in the number of antibodies. Therefore, vaccination could be said to have induced the primary immune response.

Secondary immune response

  • The second time our body is exposed to the same pathogen, our white blood cells respond quickly. This is called the secondary immune response.
  • The response this time is quick enough to not let the person fall ill due to infection. This person is now immune to a disease or has immunity to certain pathogen or disease.

Herd immunity

It is a method to provide immunity to the larger population against a certain disease which can spread easily or are prevalent in a huge population. Making the mass immune to a certain disease ensures that it does not spread further by reducing the chance of people coming in touch with the disease-causing pathogens. This large scale vaccination to provide immunity is called herd immunity.