Registration for the 2024 Walk for Immunodeficiency is now open!

About Primary Immunodeficiency

Learn more about this group of rare genetic immune disorders that disrupt and weaken the immune system.

What is Primary Immunodeficiency?

Our immune system is supposed to protect us from infection. Elite cells patrol our bodies looking for anything dodgy or amiss. When they spot something that’s not “us,” they go into microscopic superhero mode. Capes billow in the wind as our superhero cells haul away the villains, keeping us safe for another day.

Some people are born with genetic disorders that weaken their immune systems, known as Primary Immunodeficiency Disorders. Their immune system isn’t working properly, so their superheroes can’t do their jobs. Instead, villains rampage through the body, spreading infection in their wake and making the person sick and tired.

There are over 500 of these chronic conditions and counting. Worse still, most people with PI don’t know they have it and struggle to get a diagnosis. People with PI are sick and tired of being sick and tired.

Children and primary immunodeficiencies

Children with primary immunodeficiency are particularly vulnerable. Newborns and kids may need stem cell or bone marrow transplants to help boost their immune systems. And recurring infections often mean kids can’t go to school, and families spend a lot of time in hospitals.

You’re not alone.

Whether you’re a patient or supporting a child or loved one, PI is an exhausting journey. Mental health and relationships suffer greatly without a diagnosis, treatment, and support. It can be a lonely place.

That’s where ImmUnity Canada comes in.

With members across the country, we work together to empower folks with primary immunodeficiency to live well. Through education, support, advocacy, research and community, we can give all Canadians with PI access to the resources they need to thrive.

We’re sick and tired, but we’re not alone.


The Immune System

The immune system is made of cells, proteins, tissues and organs that protect the body from disease, infection and foreign substances. This complex system is dispersed throughout the body and includes organs and tissues of the lymphatic system and white blood cells called leukocytes. There are two major subsystems of the human immune system; the innate immune system and the adaptive immune system.

The innate immune system is the genetic, inherited immune response comprised of cells that need no further training to do their jobs. It is also known as the “nonspecific” immune system because it uses the same response for all pathogens. The innate immune system is highly responsive and acts on infection quickly and reliably.

Adaptive immune responses are more specialized and take over if the innate immune system cannot destroy the pathogen. The adaptive immune response is slower because it needs to identify the threat before taking action. The advantage of the adaptive immune system is that it is more accurate and can “remember” pathogens to help prevent and respond to future infections.

Major organs in the immune system


The thymus is a small gland behind the breast bone in front of the windpipe. It is a critical part of the immune system that grows and ‘trains’ a type of white blood cell called T-cells (T lymphocytes). The thymus creates most of your T-cells in utero (before birth), and the rest are created before puberty. After puberty, the thymus gland begins to shrink and is replaced by fatty tissue.


In addition to its role in the digestive system, the liver detoxifies and cleanses the blood. As blood passes through the liver, white blood cells, called phagocytic cells, ingest bacteria in the blood. The liver also produces complement proteins that help kill bacteria, viruses and infected cells.


Tonsils are lymphoid organs and play an important part in the immune system. Humans are typically born with four types of tonsils; the adenoid or pharyngeal tonsil, two tubal tonsils, two palatine tonsils and the lingual tonsil. The tonsils are a primary defence against inhaled or ingested foreign pathogens. Microfold cells (M-cells) on the surface of the tonsils can gather antigens that a pathogen produces. From there, the M-cell sends a signal to leukocytes (B-cells and T-cells) inside the tonsil, activating an immune response.

Lymph Nodes

Lymph nodes are glands that help filter harmful and damaged cells. There are hundreds of these bean-shaped glands throughout your body, and they’re a gathering place for leukocytes to communicate with each other. Lymph nodes may become swollen when the immune system is fighting an infection.


The spleen is an important organ that stores and filters blood by removing cellular waste and old or damaged blood cells. The spleen also makes white blood cells (leukocytes) and produces antibodies.

Bone Marrow

Bone marrow is the spongy tissue inside the bones and the primary source of new blood cells (hematopoietic cells), including those necessary for the immune system.


Blood helps deliver immune cells and proteins throughout the body while carrying metabolic waste away. Blood is made of blood cells and blood plasma. On its own, plasma is yellow in colour and up to 95% water by volume; it contains proteins, glucose, electrolytes, hormones, carbon dioxide and oxygen.

Key cell types in the immune system

Stem cells

Stem cells are foundational and have the ability to develop into all kinds of specialized cells, including the various types of immune cells.

Leukocytes (white blood cells)

There are two main types of white blood cells; phagocytes and lymphocytes.

Phagocytes ingest harmful bacteria, particles, and dead or dying cells. They’re like microscopic Pac-man defenders in the bloodstream.

Lymphocytes are the brains to the phagocytes’ brawn. They help the body remember previous invasions (harmful bacteria, viruses, foreign objects, etc.) and activate the immune response.


Monocytes are a type of white blood cell that can become more specialized macrophages or dendritic cells.


Macrophages are white blood cells that can be found in essentially all body tissues, where they patrol for pathogens and are one of the first cells at the scene of infection. Through a process called phagocytosis, macrophages “eat” pathogens that do not have healthy proteins on their surface, such as cancer cells, microbes, and foreign substances. Macrophages also initiate larger immune responses and are important antigen presenters for T-cells.


Neutrophils make up 40% to 70% of white blood cells in humans and are the immune system’s first responders. Through a process called phagocytosis, neutrophils ingest microorganisms and particles. Neutrophils also send chemical signals to activate other immune system responses, such as inflammation.

Dendritic cells

Dendritic cells are antigen-presenting cells, helping T-cells identify which pathogens and cells to attack.

T lymphocytes (T-cells)

T-cells are a type of white blood cell (lymphocyte) that are “trained” by the thymus to perform special functions. There are two major T-cell sub-types: Helper T-cells and Killer T-cells (also known as cytotoxic T-cells).

Killer T-cells find and destroy cells that have been infected or damaged. Antigens help identify infected cells, and if a T-cell receptor binds to the antigen, it will release cytotoxins that kill the compromised cell. There are millions of T-cells in the body, and each one has a unique receptor that only fits with one kind of antigen.

Helper T-cells are specialized lymphocytes that send chemical messages and instructions to other immune system cells. Helper T-cells direct Killer T-cells and B-cells to multiply so the immune system can fight the infection.

B lymphocytes (B-cells)

B-cells are a type of white blood cell (lymphocyte) that can connect to antigens on the surface of the invading virus or bacteria. When a B cell binds to the antigen, a Helper T-cell creates a chemical signal telling the B-cell to replicate. Now the surge of B-cells can fight the invading pathogen. These B-cells also turn into plasma cells, which make and release antibody molecules called immunoglobulins.

Plasma cells

Plasma cells are white blood cells that make and release antibody proteins called immunoglobulins. These antibodies bind to the same antigen as the original B-cell, helping the immune system respond to specific threats.

Immunoglobulins (antibodies)

Immunoglobulins are highly specialized protein molecules that move through blood in the body, binding to particular antigens (infected cells, bacteria, viruses) along the way. This binding system allows the antibody to identify the pathogen for other parts of the immune system or neutralize it directly by surrounding it and preventing further infection.