Why don't we get sick more often? An Introduction to Immunology
- hdpgetsherphd
- Jan 19
- 3 min read
Updated: Jan 20
The world is full of germs. We encounter billions of microscopic organisms every single day. Many are harmless, while others make us sick in a variety of ways. Some are always on a mission to do so, while others don't bother unless the perfect opportunity presents itself. How is it that we (mostly) stay healthy?
Important Terms to Know:
Pathogen: Bacteria, viruses, or parasites that cause infections
Immune System: System of cells in the body designed to protect you from infection and promote healing
Innate Immunity: Factors serving as first line of defense against danger and disease
Innate Immune Cells: Serve on the front lines to detect threats and be first responders to danger
Adaptive Immunity highly specialized defenses your body develops after encountering danger
Adaptive Immune Cells: Highly trained immune cells
Antibodies: Specialized flags secreted by adaptive immune cells (B cells) to tag pathogens for clearance
From time to time, we all run into the dreaded sore throat, cough, or upset stomach. You may ask yourself, “Why is this happening to me right now? I don’t have time for this!” Lots of illnesses that we get as humans are caused by microorganisms such as bacteria, viruses, and parasites. We refer to these microorganisms that cause disease as pathogens. Getting infected with a pathogen can lead to a variety of symptoms. While some of these symptoms are caused by pathogens directly, others, such as fever and swelling, are actually a result of your immune system defending you!
The immune system describes a network of cells throughout the body that protect you from infection and promote healing. Unlike other systems in the body, the immune system lives all over your body and is not fully restrained to specific organs. It is composed of many cell types, all of which have very specific jobs to help protect you from infections. As immunologists, we refer to these cells in two main groups: Innate and Adaptive.
Innate immunity describes the body's first line of defense against danger and disease. While this includes things like skin or mucus as barriers to entry, there are also immune cells with designated roles in innate immunity. Innate immune cells serve on the front lines to detect threats, and jump into action as the first responders to danger. At points of entry like the nose and mouth, they perform surveillance. One example of an innate immune cell that performs security, surveillance, and cleanup is the macrophage. These cells live in many different areas of the body and keep watch for potential dangers. When they run into danger, they sound the alarm to call for backup. Initial backup typically comes from another innate cell, the neutrophil. Neutrophils use your blood as a highway system to get to the danger as quickly as possible. Once there, they begin to help the macrophages clean up debris produced from fighting the pathogens. Macrophages and neutrophils cannot always fight off the danger on their own; dendritic cells aid in the defense by helping to initiate adaptive immunity. Adaptive immunity describes highly specialized defenses your body develops after encountering danger.
Dendritic cells serve many of the same functions that macrophages and neutrophils do, but are also especially good at training our adaptive immune cells. Adaptive immune cells specifically fight the enemy at hand and nothing else. This is one main difference between innate and adaptive immune cells; innate cells can fight many kinds of danger instead of one very specific one. More simply, innate immune cells are the security on the border and soldiers on the front line, while adaptive immune cells are the special forces. These special forces are split into two main cell types: B cells and T cells.
T cells come in two main flavors. Cytotoxic CD8 T cells, can act as assassins that directly kill infected cells. CD4 T Cells, also known as helper T cells, work to coordinate immune responses tailored to the threat. One specific subset of CD4 T cells interacts with B cells to make specific antibodies. Antibodies stick to pathogens and flag them for clearance. Antibodies can also prevent pathogens from causing more damage, referred to as “neutralization.”
These core immune cells, along with other rarer types, are essential for creating a coordinated and effective immune response. Together, they are able to defend against the innumerable pathogens we encounter throughout life. As an immunologist, I have dedicated my career to learning about and expanding our knowledge of these critical cells. They are vital not only for protecting us from infectious disease, but also fighting cancer and healing wounds. Conversely, they can also be the cause of autoimmune diseases like multiple sclerosis (MS), Lupus, and alopecia. It is critical for us to explore and gain a deeper understanding of how these cells function to continue improving medicine and save lives.
Comments