The previous article dealt in detail about innate immunity. This article is about another type of immunity known as the acquired immunity.

The acquired immunity, unlike the innate immunity, is not present from birth. As the name suggests, it is the immunity that we acquire throughout our lives. This immunity is acquired through experience and learning. In order to understand the previous statement, it is essential to know about primary and secondary infections.

The first encounter with the foreign agent is known as the primary infection. Since this pathogen is new to the immune system, it does not know what to do and hence it produces a generalized response through innate immunity. Once the pathogen is driven away from the body, certain information related to this encounter is stored in the memory of the immune system.

If the same or a similar pathogen enters into the body, the memory is triggered and a strong & quick response is generated which kicks away the pathogen faster than before. Hence the immune system has learned to defend from a new pathogen through learning. This is known to be a secondary infection.

These two combine together to form the natural active acquired immunity which is the immunity acquired as a result of diseases. In most of these cases, innate immunity fails and we get sick. During the recovery phase, the immunity is good and the activity is stored. Hence we may not get these diseases for a long period. The following diseases fall into this category:-

  • Polio
  • Chicken pox
  • Measles
  • Influenza
  • Common cold (not effective since there are several strains of viruses)

There are two characteristics in this which are:-

  • Latent period= time in which no response is seen (required for activation)
  • Negative response= time in which there is reduced response

The second type is the artificial active acquired immunity. This is similar to that of the first type with a slight change. In this case, we are artificially introducing pathogens into the body. But these pathogens have undergone a major modification. Their disease-causing ability has been genetically removed. Still, these are non-self for the immune system but they do not cause infections. Hence the immune system produces responses similar to that of natural active. These artificially induced pathogens are called vaccines. These help to induce immunity in our bodies. There are three types of vaccines:-

  1. Live
  2. Dead
  3. Products

I will be writing a separate article regarding vaccines.

The third type is natural passive acquired immunity. This is the immunity that we get from a natural source. You might have the answer. It is indeed the milk from the mother. Breast milk is rich in immunity cells especially immunoglobulins. A better idea will be in the article upon the immunity cells. This can provide immunity to the newborn up to 3 years but after three months it deteriorates since the child starts to develop immunity.

The last type is artificial passive acquired immunity. In this type, we get immunity (immunoglobulin) from an artificial source. These immune cells play a major role in identifying and binding to the pathogens and aid in phagocytosis. Don’t worry this process will be covered in the subsequent articles. There are three types in this namely

  • Hyperimmune sera- from animal or human source
  • Convalescent sera- from a recovering patient
  • Pooled human gamma globulin- from a healthy person

It is important to understand that the word active refers that the body is developing immunity and passive refers that we are providing immunity. The words artificial and natural refer to the source. There is one called combinational immunity (active+passive) in which the passive immunity provides protection until the active immunity activates (latent response).

Till now we have seen several types of immunity, the next article will be on the immune cells, the guys who are behind all these.