© Suburban Science 2021

• The immune system is a set of specialized cells that works with the lymphatic system to fight off foreign substances that enter the body.
• These foreign substances are known as pathogens.

• 1. Innate (Non-specific) defenses
• Work quickly, but are not specialized for individual pathogens
• Skin
• Mucous Membranes
• 2. Acquired (Adaptive) defenses
• Work slowly, but provide specialized and long-lasting defense against pathogens
• Humoral Immunity
• Cell-mediated Immunity

• Innate resistance starts with barriers.
• External barriers: prevent pathogens from entering body
• Skin:
• Keratinized cells create a physical barrier
• Skin produces oil and sweat which inhibit growth of bacteria

2. Mucous membranes
• Mechanical elimination- mucus physically traps pathogens and cilia of the respiratory tract can sweep them towards the mouth for removal.
• Secretions- gastric juice from the stomach, saliva, and tears all contain enzymes that kill pathogens.

Tears contain lysozyme, an enzyme that kills bacteria by destroying their cell walls.

2. Internal barriers: activated once pathogen passes into body tissues.
• Phagocytes: “eat” foreign invaders
• Neutrophils: kill bacteria then die (creating pus)
• Macrophages: move with cytoplasmic extensions to ingest pathogens.

• Natural Killer Cells
• Lyse (explode) infected or abnormal body cells based on a lack of “self” surface receptors
• Inflammation
• Basophils & Mast Cells stimulate the blood vessels to dilate/widen
• Swelling (edema) allows macrophages to quickly arrive through vessels
• Pyrogenic chemicals cause fever, which increases cell metabolism to speed up repair

• Antimicrobial proteins
• Complement proteins- work with other defenses by lysing pathogenic bacteria or marking pathogens for easier phagocytosis (a process known as opsonization).
• Interferons- warning signal proteins secreted by virally-infected body cells
• Interferons are a type of cytokine. Cytokines are the chemical signals used to help cells communicate during an immune response.

• Innate immune defenses are not specialized to detect particular pathogens. The skin & mucous membranes provide an external barrier while immune cells activated by inflammation & antimicrobial proteins fight pathogens once they pass into body tissues.

• If the non-specific defenses don’t stop the infection, the body will create an immune response specific to that pathogen.
• Substances that trigger this response are called antigens.
• The cells responsible for this specific response are called lymphocytes. Lymphocytes produce antibodies that match certain antigens.

• The acquired immunity portion of the immune response must be able to:
1. Discriminate between self and non-self antigens.
• Lymphocytes that act against self-antigens are destroyed.
2. Recognize a specific antigen among trillions of possible substances.
• Each lymphocyte only has surface receptors for one antigen.
3. Generate a large diversity of antibodies so any possible substance can be recognized and eliminated.
4. Provide memory of antigens.
• A second exposure to an antigen is immediately recognized and the infection is barely noticed.

• 1. Humoral Response
• Involves B-cells
• Responds to antigens before they infect body cells
• 2. Cell-mediated Response
• Involves T-cells
• Responds to body cells that have already been infected with foreign pathogens

• Acquired immunity is triggered by specific antigens. Lymphocytes (B and T cells) recognize the antigen, produce a large number of antibodies and remember the antigen for future infections.

Name: B-cell

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Superpowers:

Ability to recognize

invading antigens and

clone itself

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Mature in: Bone Marrow

• 1. B-lymphocytes (B cells) recognize a foreign antigen.
• 2. B cells rapidly divide creating cloned plasma B cells and memory B cells.
• Plasma B cells can secrete antibodies at a rate of 2,000 per SECOND!
• 3. Memory B cells are long-lived and produce a swift and strong response if the same antigen is encountered in the future. (“secondary response”)
• 4. The antibodies produced by the plasma B cells can:
• Neutralize the antigen by physically surrounding it
• Immobilize the antigen by agglutination (clumping)
• Activate macrophages to destroy antigen

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• Immunity can be earned or borrowed.
• Active immunity is earned because it is developed by the creation of our own antibodies.
• Natural active immunity occurs when we contract an infection.
• Artificial active immunity occurs when we are given a vaccine.
• Passive immunity is when we borrow the immunity that another individual has already created.
• Natural passive immunity occurs when antibodies are passed from a mother to child through breastmilk or the placenta.
• Artificial passive immunity occurs when we are injected with antibodies from the blood serum of an individual that has already been infected.

• Humoral immunity involves the activation of B-cells. Once activated by a foreign antigen, B-cells produce both cloned plasma B-cells and memory B-cells for future infections. Immunity can be earned through active immunity or borrowed from another through passive immunity.

• In order to amplify the immune response, B-cells can also act as antigen-presenting cells.
• Antigen-presenting cells engulf antigens and present pieces of the antigen to other immune cells.
• This is like sounding the alarm for an infection to recruit more warriors for the fight.
• Antigen-presenting cells include B-cells, macrophages, and dendritic cells.

• The antigen fragment is presented on a receptor known as an MHC-II (major histocompatibility complex-2).

• T-cells will bind to this MHC-II and mount a stronger response against the antigen.

Name: _T-cell_____

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Superpowers:

Detect and kill infected

body cells

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Mature in: _Thymus_

• 1. After the antigen-presenting cells display the foreign antigen to a helper T-cell, the T-cell is activated.
• 2. A signaling cascade begins, creating more helper T-cells and memory T-cells.
• 3. Some of the cytokine signals activate cytotoxic T-cells, which bind to infected body cells and cause apoptosis.
• 4. Regulatory T-cells release chemicals to slow the immune response after the antigen is destroyed.

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• In a secondary infection (re-infection with a previous pathogen), the body uses the Memory B and Memory T cells to react to the infection more quickly.
• Often, a person with a secondary infection will not even show symptoms.
• Sometimes, the symptoms will appear, but recede more quickly.
• Examples: cold viruses, flu
• Vaccines can help the body mimic the first infection. Thus, when the infection is encountered, the body has already produced the B and T cells to fight it.

• Antigen-presenting cells provide fragments of the infecting antigen to helper T-cells. After activation, the helper T-cells signal the formation of memory T-cells, cytotoxic T-cells, and regulatory T-cells. If the antigen is encountered again, the memory T-cells will mount a quick response.