The Four Lines of Defense — Immunology #2
The immune system is made up of four lines of defense to keep you alive and healthy.
The immune system is an amazing but very complex system that works all day, every day, to keep us alive.
By knowing how the immune system functions you will be able to understand how medications and vaccines work, as well as appreciate the healing process (which can sometimes be a pain, literally).
In the last article Why Should I Care About My Immune System? — Immunology #1 we discussed why the immune system is important and had a brief overview of the immune system as a whole.
In this article we’ll take a look at the four lines of defense that make up the immune system.
Important Terminology
Here is a list of some terms that will come up in this article.
The Four Lines of Defense
The immune system has two arms: the innate and the adaptive immune system. These two parts are made up of the 4 lines of defense.
The First Line of Defense: Host Barriers
Your body contains a number of ‘host barriers’ to prevent pathogens from invading in the first place.
There are a couple of different kinds of host barriers your body has:
- Physical barriers
- Chemical barriers
- Microbiological barriers
If these barriers are breached, the second line of defense kicks in.
The Second Line of Defense: Sensor Cell Activation
Sensor cell activation is the second part of the innate immune system. As soon as your body detects a pathogen has breached the first line of defense, the sensor cells of the innate immune system react immediately.
The sensor cells travel to the site of injury or infection and attack, devour, and digest any pathogen. This attack is non-specific. This means the sensor cells attack many different pathogens in the same way. They also attack aggressively. The aim is to get the invading pathogen out of your body as fast as possible.
The Third Line of Defense: Cell- and Antibody-Mediated Immunity
The third line of defense is when the adaptive immune system kicks in. This part of the immune system typically will start within hours of exposure to a pathogen. It is activated by the innate immune system.
Cell- and antibody-mediated immunity is specific. This means that the immune cells involved in this part of the immune system detect specific strains of bacteria or specific viruses and launch an attack specified for that pathogen.
The Fourth Line of Defense: Immunological Memory
Once the immune system has undergone cell- and antibody-mediated immunity, some of the cells from this stage become ‘memory cells.’ These cells hang around in the body for years or even your entire lifetime. Memory cells are ready to strike if they detect the same pathogen again in the future.
Memory cells are specific for a particular pathogen, just as the cells in the third line of defense are.
Fun fact: Immunological memory is the reason that vaccines work to protect against many diseases. It is also why some diseases only infect people once in their lifetime. For example, most people will only experience chickenpox once. This is because the body generates immunological memory cells that stay in the body and fight the pathogen that causes chickenpox if you are re-exposed, before you experience the symptoms.
This is just a brief overview of the four lines of defense in the immune system. We’ll go into more detail in future articles.
To Quickly Summarise This…
The immune system is made up of two arms: the innate and adaptive arms. Within these two parts of the immune system, there are four lines of defense. Each of these lines of defense plays a crucial role in protecting your body against invading pathogens. (see the image at the beginning of this section).
The first two lines of defense are part of the innate immune system. The innate immune system acts immediately to invading pathogens and is non-specific.
The third and fourth lines of defense are part of the adaptive immune system. The adaptive immune system takes a bit longer to get started but it is specific to the pathogen. It also helps to protect you against infection from the same pathogen in the future.
Conclusion
Well, that was a lot of information to take in.
Don’t worry, everything mentioned in this article will be discussed again in the future. This article is just to give you a general overview of the structure of the immune system.
Here are the key takeaways from this article:
- The immune system has two parts: the innate and adaptive parts
- There are 4 lines of defense: two in the innate and two in the adaptive parts of the immune system
- The 4 lines of defense are:
- Host barrier
- Sensor cell activation
- Cell- and antibody-mediated immunity
- Immunological memory
In the next article, we’ll take a look at some of the key players of the immune system: the sensor cells.
Other articles in this series
