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Immune system

Learning goals?

How does our skin protect us from pathogens?

What are the different jobs of white blood cells?

How does our body recognize pathogens?

How can we train our immune system to recognize potential threats?


antibody, antigen, WBC, pathogen, macrophage, phagocytosis

Skin is a barrier to disease

Our skin is a non-specific defense. It prevents pathogens from entering your body.

Pathogens are any microscopic particles that can reproduce in your body and cause disease.

1: Skin is ruptured. Pathogens enter & endanger our body.

2: Red blood cells are attracted to the cut (which will cause redness and swelling)

3: Platelets and fibrins create a blood clot, sealing the wound.

4: Marcophages (WBCs) come in. They are a type of white blood cell that engulf (“ooze around and surround”) anything that they don’t recognize.

5: Then they digest this stuff, destroying it.

Phagocytosis is the name of this process, i.e. phagocytosis is the way that macrophages engulf and digest pathogens.

Here is what it looks like when macrophages come to a cut in your skin, to protect you from pathogens.

Pin skin histamines inflammatory_response


Specific defenses: WBCs and antibodies

Our immune system has many different types of WBCs (white blood cells) Their jobs:

1) Identify pathogens

2) Tag pathogens for destruction by other WBCs

3) Destroy pathogens like Pac Man: phagocytosis (by eating it)

4) Make antibodies

How do cells recognize pathogens?

Antigens are protein or sugar “tags” found in all cell membranes (lipid bilayer.)

Each has their own job. They’re there for a reason.

Our immune system has evolved to recognize the shape of every one of these.

If they recognize these antigens as “self” (part of you) then they do nothing.

If not then they are “non-self” (not part of you), and therefore targeted for destruction.

antigens on cell membrane

antigens on cell membrane

What antigens will not be recognized?

* those on pathogens

* those on cancer cells

* On rare occasions, a mistake occurs:  WBCs fail to recognize one of your own normal body cells. So then your immune system attacks part of your own body. That is an auto-immune disease.



Y-shaped proteins, made by some WBCs, to attack pathogens.

An antibody can attack one and only one type of pathogen: The antibody’s shape must fit its target (lock and key model).

Antibody Immune Response by Nucleus Medical Media

“The animation begins by showing normal red and white blood cells flowing through the blood stream. Next, a single pathogen appears onscreen slowly moving toward its destination on the surface of a cell.”

“The tubular extensions on the pathogen are surface proteins which attach to corresponding surface proteins on a white blood cell, or leukocyte. As the animation continues, more pathogens continue to attach to the white blood cell, rendering it ineffective.”

“During the immune system response, Y-shaped antibodies begin attacking the pathogen, binding to its surface proteins as the pathogen attempts to anchor to the blood cell. The antibodies completely block the pathogen from attaching to the blood cell, “tagging” the pathogen so that one of the immune system’s leaner cells, a macrophage, appears onscreen to engulf and digest the pathogen.”

Here is the source video Antibody Immune Response | Nucleus Medical Media, on Youtube


Here we see a WBC (macrophage) tracking down and engulfing a bacteria, amidst RBCs.

Phagocytosis immune system bacteria

Immune system pathways


Some types of WBCs work with other types of WBCs.

Once a WBC eats a cell, it displays broken bits of the destroyed pathogen on their surface.

This stimulates Helper T-cells.

Helper T-cells don’t kill pathogens directly, they stimulate other WBCs to engage.

Version 1:

Helper T cells stimulate Killer T cells 

Killer T cells find infected cells and kill them: They release enzymes into pathogens causing them to die.

Killer T-Cells


Helper Cell Immune System Plasma antibodies memory cells

Version 2

Immune system cytotoxic plasma memory antibody

Innate and adaptive immune systems

Vertebrates have both of these types of immune systems.

Innate immune system

This is an older evolutionary defense strategy. It is the dominant immune system in plants, fungi, insects, and primitive multicellular organisms.

Recruiting immune cells to site of infection

    Does this by making special molecules called cytokines

Activation of the complement cascade – A series of steps that enhances (complements) the ability of antibodies and phagocytic cells.

Identification and removal of foreign substances, by specialized white blood cells.

Antigen presentation

Acting as a physical and chemical barrier to infectious agents; via physical measures like skin or tree bark and chemical measures like clotting factors in blood or sap from a tree.

Adaptive immune system

Evolved in early vertebrates.

Allows for a stronger immune response, because the body has immunological memory. This means that each pathogen is “remembered” by a signature antigen. Should a pathogen infect the body more than once, these specific memory cells are used to quickly eliminate it.

Innate and Adaptive Immunity Immune system

Image from stemcellimmuneregenerative.com/what-is-the-immune-system


Our lesson on vaccines.

Herd immunity


It’s what happens when your immune system reacts to something that’s usually harmless. Those triggers, which doctors call “allergens,” can include pollen, mold, and animal dander, certain foods, or things that irritate your skin.

An allergic reaction starts when you come into contact with a trigger that you inhale, swallow, or get on your skin.

In response, your body starts to make a protein called IgE, which grabs onto the allergen. Then histamine and other chemicals get released into the blood. That causes the symptoms you notice. Your symptoms depend on how you’re exposed — through the air, your skin, food, or through an insect sting.

  • from WebMD, Allergies: Basic Info You Need to Know

Allergies: BioNinja

Auto-immune diseases

In autoimmune diseases, the body’s immune system attacks one’s own body.  There are many different auto-immune diseases. Each has a separate cause.

See our article on autoimmune diseases.

Related topics

Herd immunity

Mysterious connection between the immune system and mental illnesses.

Types of immunity


  • Naturally antibodies are transferred from mother to child
    • Through the placenta before the baby is born
    • Through milk after birth
  • Artificial Passive Immunity à injecting antibodies from other animals/humans already immune to disease
    • Snake venom


  • Naturally antibodies are produced during an infection in response to antigens
  • Artificially by vaccines
  • Vaccines à substance consisting of weakened, dead, or incomplete portions of pathogens/antigens that when injected cause an immune response
  • Vaccines produce immunity because it prompts the body to act like it is infected

For further reading

Viral Attack! Comic book story of our immune system

External resources

The innate and adaptive immune systems: Interactive graphic

Nobelprize.org Immunity

Learning Standards

Massachusetts Comprehensive Health Curriculum Framework

Students will gain the knowledge and skills to select a diet that supports
health and reduces the risk of illness and future chronic diseases. PreK–12 Standard 4
8.1 Describe how the body fights germs and disease naturally and with medicines and
8.2 Identify the common symptoms of illness and recognize that being responsible for individual health means alerting caretakers to any symptoms of illness.
8.5 Identify ways individuals can reduce risk factors related to communicable and chronic diseases
8.6 Describe the importance of early detection in preventing the progression of disease.
8.7 Explain the need to follow prescribed health care procedures given by parents and health care providers.
8.8 Describe how to demonstrate safe care and concern toward ill and disabled persons in the family, school, and community.
8.13 Explain how the immune system functions to prevent and combat disease

Interdisciplinary Learning Objectives: Disease Prevention and Control
8.a. (Law & Policy. Connects with History & Social Science: Geography and Civics &
Government) Analyze the influence of factors (such as social and economic) on the treatment and management of illness.

Benchmarks for Science Literacy, AAAS

The immune system functions to protect against microscopic organisms and foreign substances that enter from outside the body and against some cancer cells that arise within. 6C/H1*

Some allergic reactions are caused by the body’s immune responses to usually harmless environmental substances. Sometimes the immune system may attack some of the body’s own cells. 6E/H1

Some viral diseases, such as AIDS, destroy critical cells of the immune system, leaving the body unable to deal with multiple infection agents and cancerous cells. 6E/H4

Vaccines induce the body to build immunity to a disease without actually causing the disease itself. 6E/M7** (BSL)

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