In our daily life, we encounter several biological and environmental intruders regularly. These trespassers may enter our body through our skin or breath or mouth, and they may have the ability to harm us. Now, more than ever – when the world is dealing with a global pandemic – it is important to understand how our own physiology safeguards us.

The human physiology has a system in place which wages war against any foreign substance; this ‘inbuilt shield’ that protects us is the immune system. Read more about why some people have a relatively weak immune system here and the role of genetics in the immune system for some additional context. 

What is immunity?

Immunity is the ability of our body to fight against, or get rid of, foreign organisms or abnormal cells or substances that have the potential to cause us harm. The immune system is the entire network of cells and tissues that work together like a well-oiled machine to protect us from any harm from outside or inside the body.

So how does the immune response work?

There are antigens – substances upon exposure to which the immune system releases antibodies to prevent any harm to the organism. For example, when we are exposed to a cold-causing virus, which is an antigen, our body releases antibodies to fight the virus to get over the cold. 

In other words, we can say that antibodies are the ammunition our immune system uses to resist the antigen attack; the immune system is our body’s defence mechanism.

What are the different types of immunity?

The immune response can be classified into two types (1)

  • Innate immunity or non-specific immunity
  • Adaptive immunity or specific immunity 

What is innate immunity?

The innate immune system consists of a non-specific response to a wide variety of foreign substances. Even if the immune system has been exposed to the same foreign material earlier, the innate immune response will start from square one – it has absolutely no immunologic memory. 

Think of it this way: it uses the very same sort of weapons, whoever the intruder; it does not remember what worked well in destroying any particular intruder the last time it attacked.

Innate immunity can be divided into four types(2)

  • Anatomical barriers (skin and mucous membranes)
  • Physiological barriers (body temperature, pH levels of the stomach and so on)
  • Phagocytic/endocytic barriers
  • Inflammatory barriers

The innate immune system is the first line of defence of our body(3); the soldiers first seen at the scene of the ‘attack’ are the innate immune system cells – neutrophils and macrophages. 

How do these innate immune cells operate? 

Innate immune cells secrete enzymes that digest proteins, and they are capable of releasing reactive chemicals that destroy the intruders. After terminating the intruders, they consume the remains and digest them; this process is known as phagocytosis. That means they destroy and clean up any debris in the body that remains after the destruction of the intruders(3) .

Suppose a certain bacteria attacks our body – the innate immune system immediately swing into action and put up a fight against the bacteria to eliminate the problem.

What is adaptive immunity?

The more sophisticated artillery our immune system possesses belongs to the adaptive immune system. The adaptive immune response is very specific for certain types of antigens; it remembers the intruder and stores the information pertaining to it in its memory. When exposed to the same intruder over a period of time, the response becomes stronger and faster. 

Let’s say we have taken a vaccination shot for the flu. When the flu virus attacks us later on, our body remembers the virus from the vaccine we had taken earlier and makes antibodies from memory and helps fight the flu virus. That’s adaptive immunity in action for you!

The two major types of cells or lymphocytes that are responsible for the adaptive immune system are B cells and T cells(1). These cells are generated in response to specific microbes from immunological memory, or from previous exposure to the same antigens(4).

If the innate immune system, which is the first line of defence on the scene, does not work, then comes in the next line of defence – lymphocytes.  These lymphocytes symbolise the functions of adaptation and memory. Lymphocytes make it possible for the immune system to remember individual antigens so that if the same antigens attack again, the reaction would be faster and more specific(3)

How are the innate and adaptive immunity systems linked to each other?

Innate immune system cells perform one more function – they process the antigen so that the next line of defence, the more specific adaptive immune system cells, can take over and finish the job of annihilating the invader. This work is done by antigen presenting cells (APC’s) and the most efficient APC’s are the dendritic cells of the innate immune system(5).  

Simply put-

The immune system is a very complex system and interest surrounding it has naturally exploded in recent times, especially since the global spread of the novel COVID-19 virus. We break down its multifaceted design and delve into several aspects such as adaptogens and immunity and measures to boost immune system in our other articles in this series.