Innate versus adaptive immunity: What’s the difference?

The human immune system is complex, with multiple organs, cell types, and proteins all working together to protect the body from threats. Immunologists think of the immune system as two connected sets of responses:innate immunity and adaptive immunity. They’re like two parts of an army, using different strategies to tackle threats but also communicating with each other to be effective.

Innate immunity describes the parts of the immune system that aren’t specific to any particular threat and that don’t need any training to do their job. A fever, for example, is an innate inflammatory response that kills many different types of germs without the body needing training to spike one. If your immune system is like a big city library, these parts of the immune system are like the guards at the door checking your bag before you enter and ensuring you don’t cause any disturbances.

Adaptive immunity describes the parts of the immune system that are ‘adapted’ to fight one particular threat, like a specific species of bacteria. An example of an adaptive immune response is when your body creates pus as it fights against a certain type of bacteria invading a cut. The adaptive immune system parts are the librarians in the big city library who catalog new books, remember the specific location of every item, and know exactly how to find specialized information.

The innate and adaptive immune response work in tandem to fight infection. Innate immunity essentially gives your adaptive immune system time to train and ramp up a response to the specific threat. The innate immune response occurs within about four hours, whereas the adaptive immune response is slower, occurring within about four to 14 days.

Most people with primary immunodeficiency (PI) have more trouble with their adaptive immune system, specifically with their T cells helping their B cells to make antibodies. While PI can affect both the adaptive and innate systems, antibody deficiencies make up about half of all PI cases, making them the most common.

People with antibody deficiencies include diagnoses like common variable immune deficiency (CVID), specific antibody deficiency (SAD), X-linked agammaglobulinemia (XLA), selective IgA deficiency, hyper IgM syndrome, and IgG subclass deficiency.

Antibody deficiencies can lead to bacterial infections like pneumonia, sinus and ear infections, gastroenteritis, skin infections, and sepsis. Other common complications include diarrhea, fatigue, autoimmune conditions, and chronic lung disease.

People with PI who have trouble with their innate immune response cannot launch an immediate first-line defense against germs. Immune cells such as neutrophils, monocytes, macrophages, and natural killer (NK) cells, along with proteins in the complement system, are missing or impaired.

When the innate immune response isn’t working properly in a person with PI, that person can be vulnerable to difficult-to-treat, severe, recurring bacterial and fungal infections, particularly deep abscesses of the skin or organs, persistent thrush, and infections of the respiratory tract.

Chronic granulomatous disease (CGD), for example, is a PI that affects the innate system and prevents neutrophils and phagocytes from producing a chemical necessary to kill fungi and bacteria. People with CGD are especially prone to developing severe fungal and bacterial infections in the lungs, skin, and lymph nodes. Another common innate-affecting PI is leukocyte adhesion disorder (LAD) which affects neutrophil function and leads to bacterial infection and severe dental disease.

PIs that impair the innate response due to lack of NK function are more prone to viral infections from the Epstein-Barr virus, cytomegalovirus (CMV), herpes virus, chicken pox, and shingles. Other PIs that affect the innate system include complement deficiencies, severe congenital neutropenia, and toll-like receptor signaling pathway deficiencies.

Knowing whether your adaptive or innate immune system response is affected by your PI is important for understanding not only symptoms but also treatments. Compromised adaptive immune responses, for example, respond to treatment with prophylactic antibiotics and immunoglobulin replacement therapy. Those with innate immune response problems (or those with challenges in both their innate and adaptive responses) may need different treatments such as prophylactic antibiotics and antifungals, steroids, interferon gamma-1ba (for CGD), and even bone marrow transplant or gene therapy.

To learn more about your immune system function, take the immune system self-assessment. The self-assessment can provide a launching point for further conversations with your medical provider about symptoms that may relate to PI and how the condition compromises your adaptive and innate immune system responses.