Why Do Primary Immunodeficiencies Cause Autoimmune Disease?

It is frustrating and counterintuitive to learn that your immune system is both too weak to fight off infections and too aggressive when it comes to your own body. However, a primary immunodeficiency—now frequently called an inborn error of immunity (IEI)—rarely means your immune system is uniformly “weak” or turned off. Instead, it is better understood as a regulatory problem, or immune dysregulation ^[1]. Particular genetic defects can impair your body’s infection defenses while simultaneously breaking the internal regulatory mechanisms that stop the immune system from mistakenly attacking healthy tissue ^[2].

Because there are hundreds of different inborn errors of immunity, they do not all cause autoimmunity, and they do not all follow the same pathway. The way immune dysregulation happens depends entirely on your specific diagnosis and genetic defect ^[3]. Furthermore, while autoimmunity involves the immune system creating targeted attacks against your own cells, some IEIs cause autoinflammation, which is excessive, generalized inflammation driven by the innate immune system without specific autoantibodies ^[4]. Below are several possible mechanisms that explain how different immunodeficiencies can lead to immune dysregulation.

The Thymus Training Camp: Central Tolerance

T-cells, a crucial type of white blood cell, mature in an organ called the thymus. This process establishes central tolerance, which is the ability of the immune system to recognize and tolerate your own body ^[5].

In a healthy thymus, many strongly self-reactive T cells are destroyed before they can leave and circulate in the blood ^[5]. In certain specific disorders, such as AIRE-related disease (APECED), this central training process is defective ^[6]. The immune system fails to properly screen these cells, allowing T cells that target your own organs to escape into the bloodstream ^[6].

Regulatory Traffic Cops: Peripheral Tolerance

Even with a healthy thymus, some mildly self-reactive immune cells naturally slip out into the bloodstream. In a healthy body, specialized immune cells called regulatory T-cells (T-regs) act as traffic cops, suppressing self-reactive cells to maintain peripheral tolerance ^[7].

Certain inborn errors of immunity involve genetic mutations (such as in the FOXP3 gene causing IPEX syndrome) that disable or reduce these T-regs ^{[7] [8]}. Without these regulatory traffic cops, the immune system loses a critical set of brakes, leading to widespread autoimmune conditions ^[8]. However, autoimmunity in many other primary immunodeficiencies is driven by completely different pathways rather than a lack of T-regs ^[1].

B-Cell Dysregulation and Antibodies

B-cells create antibodies, which are proteins that target and neutralize specific germs. In conditions like Common Variable Immunodeficiency (CVID), B-cell function is altered. Often, the immune system fails to produce enough protective antibodies to prevent infections ^[9].

Simultaneously, impaired B-cell regulation can allow the production of autoantibodies—antibodies that mistakenly target your own blood cells, joints, or organs ^[10]. CVID is highly variable: while many patients experience antibody deficiency alongside autoimmune cytopenias (low blood cell counts), not everyone with CVID develops autoimmune disease, and autoimmune manifestations can sometimes occur without universally high autoantibody levels ^{[9] [10]}.

Failure to Clear Out: Apoptosis

When your body fights an infection, it multiplies immune cells to handle the threat. Once the germ is defeated, those extra cells are supposed to safely self-destruct in a programmed process called apoptosis ^[11].

In some IEIs, such as Autoimmune Lymphoproliferative Syndrome (ALPS), this self-destruct signal is impaired ^[11]. Activated immune cells build up in the body and become overactive, often contributing to enlarged lymph nodes and autoimmunity targeting the patient’s red blood cells or platelets ^[11].

Infection Triggers and Bystander Activation

Because individuals with PI are prone to frequent infections, their immune systems are often battling invaders. In some cases, this persistent state of high alert is proposed to trigger autoimmunity through mechanisms like molecular mimicry, where a germ looks structurally similar to your own healthy cells, or bystander activation, where the generalized inflammation from an infection accidentally damages nearby healthy tissue ^[6]. This is only one proposed mechanism in selected diseases, and not every new symptom is caused by an infection.

Safety and Moving Forward

Treating an immunodeficiency alongside an autoimmune condition is a delicate balancing act tailored to your specific diagnosis ^[12]. Your care plan may include infection prevention, targeted immune therapies, or immunoglobulin replacement—which can provide both missing antibodies and immunomodulatory effects.

Safety Note: Never stop your immunoglobulin replacement, preventative antibiotics, or immunosuppressive medications without speaking to your clinician. Because it can be difficult to tell the difference between an autoimmune flare and an infection, contact your care team promptly if you experience severe breathing difficulty, significant bleeding, confusion, a high fever, or rapidly worsening illness.