Chapter 14: The Innate Immune Response

What is innate immunity?

Refers to defenses that are present at birth, providing a non-specific response to most microbes.

Describe innate immunity memory component

Lacks a memory component and cannot recall previous contact with an invader

When is innate immunity active?

Always present and active before an infection occurs, enabling a rapid response

How does innate immunity act against microbes?

Acts in a non-specific manner, meaning it responds to all microbes in generally the same way

First Line of Defence list of physical barriers

• Skin

• Mucous Membranes

• Fluid flow

First Line of Defence list of chemical barriers:

• Acidity of body fluids and skin

• Lysozyme, lactoferrin

• Defensive

• Normal microbiota

What is the purpose of first line defenses?

Physical and chemical barriers that prevent microbes from entering the body.

How does the skin act as a physical barrier?

The outer surface of the skin consists of dead cells and keratin; it is frequently shed, removing microbes.

Why is dry skin an effective barrier against microbes?

Inhibits the growth of microbes, making it harder for them to survive on the surface.

Where are skin infections most likely to occur?

Moist areas of the skin or moist environments

What happens when the outer layer of skin is broken?

Microbes can enter and cause infections under the skin

How do some microbes contribute to body odor?

Consume dead skin cells and skin oils, which can result in body odor

What is the role of mucous membranes in innate immunity?

Involved in fluid or gas exchange and line tracts such as the digestive tract, offering less protection than skin

How do mucous membranes prevent infection?

They secrete mucus (a glycoprotein) that keeps the membrane moist and prevents it from cracking, trapping microbes in the mucus

What is the purpose of fluid flow in first line defenses?

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Saliva, tears, urine, and vaginal secretions help move microbes away from the body, effectively flushing out potential pathogens

What is the mucociliary escalator?

Involves cilia sweeping mucus away from the respiratory tract, helping remove trapped microbes

How does the acidity of body fluids and skin act as an antimicrobial barrier?

Stomach acid (pH 2) destroys many bacteria and toxins; skin's fatty acids and lactic acid (pH 3–5) prevent the growth of many microbes

What is lysozyme, and where is it found?

An enzyme that degrades peptidoglycan in bacterial cell walls. It is found in sweat, tears, saliva, and nasal secretions

What role does lactoferrin play in innate immunity?

An iron-binding protein in milk and mucus that makes iron unavailable, slowing microbial growth

How do defensins function as a chemical barrier?

Short polypeptides that poke holes in microbial membranes, helping to kill invading pathogens. They are produced by epithelial cells

What is the role of the normal microbiota in preventing infection?

Acquired shortly after birth, prevent pathogen growth through competitive exclusion and microbial antagonism

What are second-line defenses in innate immunity?

Components that work to eliminate microbes that have invaded body tissues, including cellular defenses, molecular defenses, fever, and inflammation

What are the main categories of second-line defenses?

• Cellular defenses

• Molecular defenses

• Fever

• Inflammation

What is the role of leukocytes in the immune system?

White blood cells, are always present in normal blood and increase in response to infection

What are phagocytes?

White blood cells that protect the body by using phagocytosis to “eat” and destroy microbes

What happens to leukocyte levels during an infection?

Increase in response to an infection to help fight off invading microbes

What is the three broad groups of Leukocytes?

Granulocytes, Mononuclear Phagocytes, Lymphocytes

What are granulocytes and what is their defining characteristic?

White blood cells that have large granules in their cytoplasm, visible with a light microscope

What are the three sub-groups of granulocytes?

• Basophils

• Eosinophils

• Neutrophils

What is the role of basophils in the immune response?

Weak phagocytes that secrete chemoattractants and release histamine, causing inflammation and allergic reactions

What is the function of eosinophils?

Destroy large pathogens, such as parasitic worms, by producing extracellular digestive enzymes to attack them

What are neutrophils and what is their role in the immune system?

Polymorphonuclear white blood cells that are strong phagocytes. They can leave the blood and migrate into tissues to destroy invading microbes

What are mononuclear phagocytes?

White blood cells that contain granules, but these are not visible under a light microscope. They include monocytes and dendritic cells

What is the role of monocytes in immunity?

Initially non-phagocytic. When they leave the blood and enter tissues, they differentiate into macrophages, which are strong phagocytes that filter out invading pathogens as blood passes through organs

What is the role of dendritic cells in immunity?

Phagocytize foreign material and present it to the adaptive immune system for "inspection," playing a crucial role in antigen presentation

What are lymphocytes?

Type of white blood cell involved in immune responses. They include Natural Killer (NK) cells, T lymphocytes, and B lymphocytes

What is the role of Natural Killer (NK) cells in immunity?

Responsible for killing infected body cells and tumor cells by targeting and attacking any body cell that displays unusual proteins on its cytoplasmic membrane

What is the role of T and B lymphocytes in immunity?

Part of the adaptive immune system.

They are responsible for recognizing specific pathogens and generating a tailored immune response. T cells help regulate the immune response and kill infected cells, while B cells produce antibodies.

What is the Complement System?

A group of about 30 proteins that circulate in the blood. These proteins work together in a cascade

How the 30 proteins that circulate the blood in the complement system works together

In cascade where the activation of one protein triggers the action of the next

How is the Complement System triggered?

Small molecules bind to the surface of invading microbes

What are the three activation pathways of the complement system?

• Alternative pathway- C3 can bind to a microbial invader

• Lectin pathway- MBL can bind a microbial invader

• Classical pathway- Antibodies can bind a microbial invader

Results of Activating the Complement Cascade:

• Opsonization

• Enhance Inflammation

• Lysis of Foreign Cells

What is Opsonization in the context of the Complement System?

When complement proteins attach to microbes, acting like a flag to attract phagocytes. This increases phagocytosis by up to 1000 times, making it easier for immune cells to clear infections

How does the Complement System enhance inflammation during an immune response?

Increase blood vessel permeability, allowing immune cells and proteins to reach the infection site more easily and also attract phagocytes to the area to help fight off the invading microbes

How does the Complement System lead to lysis of foreign cells?

Form membrane attack complexes (MACs) that poke holes in the membranes of foreign cells, leading to their destruction

What type of gram bacteria is killed by the process of lysis of forming cells? and what is not?

Kills gram negative bacteria but not gram positive

What happens during the inflammatory response to tissue damage?

Blood vessels dilate, causing fluid leakage and migration of leukocytes into the tissues. This increases blood flow, allowing phagocytes to enter, enhancing phagocytosis. It also brings platelets to form blood clots and provides nutrients for faster tissue repair.

Signs and symtoms of inflammation

• Pain, swelling

• Heat, redness

• Edema

• Loss of function

Fever is triggered by?

Toxins, LPS or chemicals produced by the immune system

What is fever results in?

Rapid muscle contraction(shivering) and increased temperature

What is fever’s benefits

• Faster phagocytosis.

• Slows growth of heat-limited microbes (e.g., E. coli growth slows at 40°C).

• Faster metabolism, aiding in healing.

  • Fever is a defense up to a certain temperature.

What is fever’s drawbacks?

Uncomfortable and could cause death gets above 43 C

When is Anti-viral Interferons(IFNs) produced?

Produced when cells detect viral RNA

When is Anti-viral Interferons(IFNs) is released?

Released by infected cells to warn neighbouring cells

What is the role of Anti-viral Interferons (IFNs) in defense against viral infections?

• Induces neighboring cells to enter an antiviral state.

• Does not help cells that are already infected.

• Infected neighboring cells undergo apoptosis to prevent viral spread.