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Immunity and infection prevention

Innate and adaptive immunity

The immune system has two “teams”. Innate immunity is a fast guard that is always ready, while adaptive immunity is a specialist force that studies the enemy and strikes precisely. This topic explains how they differ, how they work together and why, in leukemia, it matters which layer of defence is weakened.

Last updated: ~5 min read
Two groups of cells on a dark navy background: on the left, many widely scattered turquoise glowing cells; on the right, a few neatly lined-up cells in gold light.
Figure 1.Concept: the immune system’s two teams, fast guards and precise specialists.

01Short answer

Innate immunity is present from birth and responds to all germs in the same way, within minutes to hours. It includes the skin and mucous membranes, the cough reflex, stomach acid, neutrophils, monocytes, macrophages, NK cells and defence proteins. Adaptive immunity builds up over a lifetime, after infections or vaccines. It is based on B and T lymphocytes and antibodies: it recognises a specific germ, needs several days the first time, but creates memory. The two teams depend on each other: innate cells show pieces of a germ to lymphocytes, and antibodies make the work of phagocytes easier. In leukemia and its treatment, both layers can be weakened. Which layer is weakened shapes which infections are more likely and which prevention your team chooses.

02Simple explanation

Innate immunity is like a castle wall and guards on duty: always in place and reacting at once to anyone who arrives. But it does not know exactly who the enemy is.

Adaptive immunity is like a special forces unit: it first has to study the enemy, so it arrives later. But when it does, it hits the target precisely and remembers the enemy.

Innate defence includes the skin, mucous membranes, neutrophils and macrophages. The main workers of adaptive defence are B and T lymphocytes and the antibodies they make.

The two teams work together. Macrophages and dendritic cells show the germ’s “portrait” to lymphocytes. Antibodies, in turn, tag the germ so that phagocytes can find it easily.

The link with leukemia: when neutrophils are low, bacterial and fungal infections become more dangerous; when lymphocytes and antibodies are weak, some viral and other infections do. Your team chooses prevention accordingly.

03Scientific explanation

Definition: according to the NCI dictionary, innate immunity is present at birth, lasts a lifetime and is the body’s first response to a foreign substance. Adaptive immunity develops when the immune system responds to a foreign substance or germ, for example after infection or vaccination, and can prevent disease in the future.

Speed and precision: according to InformedHealth, the innate system responds to all germs in the same way and acts very quickly; for example, bacteria entering the skin through a small wound are destroyed on the spot within a few hours. The adaptive system must first recognise the germ, so it is slower, but more precise and has a “memory”.

Proteins and signals: according to MedlinePlus, innate immunity also includes proteins such as the complement system, interferon and interleukin-1, which causes fever. According to the NCI, cytokines are proteins made by immune and other cells that stimulate or slow down the immune system; they act as the “communication line” between the two teams.

Borderline cells: according to Vivier and colleagues, NK cells are classed as innate but show some features of adaptive immunity. According to the reviews by Chaplin and Marshall, dendritic cells are the main bridge linking the two systems.

04What happens in the body?

The first line of defence: barriers

According to InformedHealth, the skin and mucous membranes form a physical barrier, and acid, enzymes and mucus stop germs from growing. The movement of tiny hairs in the lungs, tears, sweat and urine also wash germs away. When chemotherapy damages the mucous membranes or a catheter passes through the skin, this barrier is weakened.

A wall made of a softly glowing translucent layer of cells on a dark navy background, with small dark particles that fail to reach it.
Figure 2.Innate immunity is a wall that rises at once against any germ.

The second line: cells and proteins

When a germ gets past the barrier, innate cells trigger inflammation: blood vessels widen, and the area turns red, swells and warms up, sometimes with a fever. Phagocytes swallow germs and NK cells destroy infected cells. This response is usually enough to stop an infection or hold it back until adaptive immunity arrives.

The third line: a precise strike

If innate defence cannot fully destroy the germ, adaptive immunity steps in. Helper T cells activate matching B cells, which make antibodies, while cytotoxic T cells destroy infected cells. After the fight, memory remains.

Several thin gold beams of light aimed precisely at a single target particle on a dark navy background.
Figure 3.Adaptive immunity recognises a specific germ and strikes precisely.

Which layer weakens in leukemia?

According to the American Cancer Society and the NCI, leukemia cells crowd out healthy cells in the bone marrow, and chemotherapy lowers neutrophils. Some treatments, such as long courses of steroids, weaken lymphocytes. In CLL, antibody production can fall. After a transplant, both layers are weak for a while.

Why is prevention individual?

According to ASCO and IDSA guidance, antibacterial and antifungal prevention may be recommended when long, deep neutropenia is expected; antiviral medicines against herpes viruses during some treatments; and prevention of Pneumocystis pneumonia during long courses of steroids and some other medicines. Your team decides what you need.

05Three lines of defence against a germ

A simplified sequence.

Barriers — The skin and mucous membranes keep the germ out.1BarriersThe skin and mucous membranes keep the germ out.
Innate cells — Phagocytes and NK cells attack within minutes to hours.2Innate cellsPhagocytes and NK cells attack within minutes to hours.
The bridge — Dendritic cells show the germ’s “portrait” to lymphocytes.3The bridgeDendritic cells show the germ’s “portrait” to lymphocytes.
Adaptive response — B and T cells strike precisely and create memory.4Adaptive responseB and T cells strike precisely and create memory.
SpeedInnate defence starts at once.
PrecisionAdaptive defence recognises the specific germ.
MemoryOnly adaptive immunity creates long-term memory.

06Comparing the two teams

FeatureInnate immunityAdaptive immunity
When it developsPresent from birthOver a lifetime, after infection or vaccination
SpeedMinutes to hoursSeveral days the first time
PrecisionGeneral, the same for all germsTailored to a specific germ
MemoryNo classic memoryYes
Main partsSkin, mucous membranes, neutrophils, macrophages, NK cellsB and T lymphocytes, antibodies
Example of weakening in leukemiaNeutropenia after chemotherapyLow antibodies in CLL, lymphopenia after steroids

* This table is simplified; in real life the two systems work in close partnership.

07Key terms

Innate immunity
Fast, general defence present from birth.
Adaptive immunity
Precise defence with memory that develops after infection or vaccination.
Barrier
The skin and mucous membranes that stop germs from getting in.
Phagocyte
A cell that swallows and destroys germs.
Complement
A system of proteins that helps tag and destroy germs.
Cytokine
A protein that carries signals between immune cells.
Interferon
A signalling protein involved in defence against viruses.
Inflammation
A response to infection or injury with redness, swelling and warmth.
Dendritic cell
A cell that bridges innate and adaptive immunity.
Prophylaxis
Medicine given in advance to prevent an infection.

08Key points

  • Innate immunity is fast and general.
  • Adaptive immunity starts slowly but is precise and has memory.
  • Barriers are the first line of defence.
  • Dendritic cells link the two systems.
  • Antibodies make the work of innate cells easier.
  • Leukemia and its treatment can weaken both layers.
  • Which layer is weakened shapes the type of infection risk.
  • Your team chooses prevention based on your situation.

09Frequently asked questions

Which type of immunity is more important?

Both. Without innate immunity, an infection would spread in the first few hours; without adaptive immunity, the body could not fully defeat a germ and remember it.

Which type of immunity does neutropenia affect?

Neutrophils are the main cells of innate immunity. When they are low, the risk of bacterial and fungal infections rises; we cover this in detail in the topic on neutropenia.

If children are born with innate immunity, why do they get ill so often?

Because their adaptive immunity is still developing: they need to get to know each new germ. According to MedlinePlus, babies are protected for a while by antibodies from their mother, which disappear between 6 and 12 months of age.

Does leukemia wipe out adaptive immunity completely?

Usually not. It is weakened to different degrees depending on the disease and treatment and often recovers after treatment. Your team follows the pace of recovery with blood tests.

Do immune “boosters” work?

There are no proven supplements that reliably boost innate or adaptive immunity. Hygiene, food safety, vaccines (with your team’s approval) and any prescribed prevention are more useful.

Which type of immunity causes fever?

Fever comes mainly from signalling proteins of innate immunity. During treatment, a fever is an emergency: call your team straight away.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. Which part of my immune system does treatment affect most?

  2. Which types of infection will I be more vulnerable to?

  3. Do I need preventive antibiotics, antivirals or antifungals?

  4. How long might it take my immunity to recover?

My questions

12Sources

  1. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: innate immunity
  2. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: adaptive immunity
  3. National Cancer Institute (NCI). NCI Dictionary of Cancer Terms: cytokine
  4. InformedHealth.org (IQWiG). The innate and adaptive immune systems
  5. InformedHealth.org (IQWiG). How does the immune system work?
  6. MedlinePlus (U.S. National Library of Medicine). Immune response
  7. MedlinePlus (U.S. National Library of Medicine). Immune System and Disorders
  8. Journal of Allergy and Clinical Immunology, 2010. Chaplin DD. Overview of the immune response
  9. Allergy, Asthma & Clinical Immunology, 2018. Marshall JS et al. An introduction to immunology and immunopathology
  10. Science, 2011. Vivier E et al. Innate or adaptive immunity? The example of natural killer cells
  11. National Cancer Institute (NCI). Infection and Neutropenia during Cancer Treatment
  12. American Cancer Society. Why Are People with Cancer More Likely to Get Infections?
  13. Journal of Clinical Oncology (ASCO and IDSA), 2018. Antimicrobial Prophylaxis for Adult Patients With Cancer-Related Immunosuppression: ASCO and IDSA Clinical Practice Guideline Update
  14. Centers for Disease Control and Prevention (CDC). Altered Immunocompetence — General Best Practice Guidelines for Immunization
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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