Bahruz Jabiyev

Cybersecurity PhD candidate at Northeastern University

Khoury College of Computer Sciences

Northeastern University


October 16, 2021

Summary: The macrophage is a cell of immune system and its ability to fight invaders can inspire us to build more effective defense techniques.

About Macrophages

Phagocytes comprise another important part of the innate immune system. These cells are specialized in phagocytosis (eating invaders) and have several types; the macrophage is one of them.

Macrophages are mainly positioned where the human body is exposed to the outside world. They reside under the skin to protect against invading microbes (e.g., as a result of a wound or a burn). They are also in our lungs to fight microbes coming from the air we inhale. They are also present in the intestines to defend us against ingested microbes. The electron micrograph below shows a macrophage extending an arm to grab a bacterium.

Taken from the book called "How the immunity system works"

A macrophage has three different states of activity. In the first state, a macrophage is in the resting mode and it functions as garbage collector. For instance, in an adult human body about a million cells die every second and macrophages keep our body clean by eating them.

When a macrophage receives a signal from another immune system player about an intrusion, it switches to the next state and becomes activated. In that state, its eating ability gets better. Once the invader is eaten, the macrophage presents a sample from the invader to let other immune system players know about the infection. For that, it positions class II MHC molecules on its own surface to display fragments of proteins from the invader.

If it receives a direct signal from an invader, it switches to the hyperactive state. For that to happen, a receptor of the macrophage should recognize and bind to a molecule on the surface of the invader. In this state, the number of lysosomes -- a cell organelle where strong enzymes and chemicals are stored -- increases, which will eventually be used to destroy the invader once it is ingested by the macrophage. Also, the production of reactive oxygen molecules is increased. Finally, in this state the macrophage can dump the contents of its own lysosomes onto an invader if it is too large to eat.

Lessons for Cybersecurity

The macrophage is a versatile cell and has different functions. The defense mechanisms we design can learn from this versatility to create less overhead and better fit the overall system.

The macrophage has different levels of activity for different levels of threat. Our defense systems can benefit from this to avoid overreacting (false positives) and underreacting (false negatives).

The ability of the macrophage to eat the invader regardless of its size is also impressive. Its techniques to eat for different sizes can teach us.


  1. Sompayrac, Lauren. How the Immune System Works. Fifth ed., John Wiley & Sons, Ltd, 2016.