Immune System

I. How Do Pathogens Cause Disease?• A. Louis Pasteur discovered that disease came from

microorganisms, living things to small to see without a microscope.

• B. Robert Koch’s studies showed that a microorganism that causes disease is better known as a pathogen and can only cause one type of infectious disease.

Ex. What causes strep throat can’t cause chicken pox.

II. Types of Pathogens

• A. There are 5 major types of human pathogens:– 1. Viruses– 2. Bacteria – 3. Protists– 4. Fungi– 5. Parasites

• B. They all can be spread through contact with a sick person, other things, or an object in the environment.

Infect & destroy healthy cells-making you sick

Smallest

III. Immune System• A. Our bodies are the perfect device for pathogens

to grow, reproduce and transport to new environments. Our immune system provides defenses to prevent this from occurring.

• B. We have two forms of immunity:– 1. Innate immunity – has no memory, always active• First line of defense & inflammatory response

– 2. Adaptive immunity – only found in vertebrates, very specific response with recognition of pathogens• Final line of defense, immune response

IV. Body’s Defenses • A. First line of defense: Innate immunity– 1. Skin – oils & chemicals in sweat kill pathogens• Invertebrates: exoskeleton , lysozyme (destroy cell walls)

– 2. Breathing Passages – lined with cilia that remove foreign particles (sneeze/cough), as well as tears

– 3. Mouth/Stomach – saliva & stomach acid kill pathogen that may be on your food.

V. Cellular Innate Defenses• A. Not only do we have natural barriers to prevent entry of

pathogens we also have several cells that work to protect us including:

• 1. Macrophages – “big eaters” found in organs that are more likely to see pathogens Ex. Dendritic cells & Eosinophils

• 2. Neutrophil cells – circulate the blood and get signals from infected cells

• 3. Natural killer cells – always in circulation detect abnormal surface proteins, release chemicals for cell death (virus/cancer cells)

• 4. Interferons – proteins produced to interfere w/ viral infections (30 different proteins)

VI. Inflammatory Response• A. Second line of defense: Inflammatory response

(innate immunity) which is a general response regardless of the pathogen that is signaled by histamine:– 1. White Blood Cells – phagocytes, cells that engulf the

pathogen & break them down by use of TLR that bind to molecules on the surface of the pathogen

– 2. Inflammation – capillaries widen increasing blood flow to area increasing white blood cell release (swelling)

– 3. Fever – pathogens can’t grow in high temp. and speeds up chemical reactions• To high of a fever = septic shock BLOOD TYPE discuss

FYI: Histamine is released any time the top layer of cells is irritated that’s why when you scratch your skin become red

VII. Immune Response• A. Third line of defense is the immune response

which is controlled by the nervous system & can distinguish between different types of pathogens

• B. The white blood cells of this response are called lymphocytes, which are classified as either:– 1. T cells (thymus gland)– recognize molecule markers

known as antigens that mark pathogens by the use of MHC that present the antigen along the surface

– 2. B cells (bone marrow)– secrete proteins that destroy pathogens called antibodies, once recognized by the antigen receptor, marking them for destruction

Humoral & Cell Mediated response

IIX. Diversity of B & T cells• A. Such diversity of both these cells is due to the

variance between the antigen receptors which is due to the variety of combinations of epitopes pathogens have along the cell membranes. – 1. Once a correct match is made the B or T cell undergoes

multiple divisions (clonal selection), as a result effector cells begin fighting off and marking pathogens (positive feedback)• B cells – plasma cells• T cells – helper T cells(make more T & B) & cytotoxic cells (release

toxins)

– 2. While others become memory cells

IV. Becoming Immune• A. Immunity is the body’s ability to destroy

pathogens before they can cause disease.– 1. Once exposed a person initiates the primary immune

response (10-17 days). After the initial exposure the body can be exposed again and the response is faster/more prolonged secondary immune response (2-7 days).

IX. Becoming Immune

• B. Your body can become immune 2 ways:– 1. Active immunity– 2. Passive immunity

• 1. Active – when your immune system produces antibodies against a pathogen, acquired either by getting the disease or being vaccinated (immunization).

It lasts for many years.• a. Vaccine – harmless

antigens, killed pathogens, are placed inside your body to produce memory T & B cells

• 2. Passive – immune system is given antibodies, only lasts within the body a short time period

XI. Disruptions in Immune System

• A. Adaptive immunity offers significant protection against pathogens but it is not perfect. Examples when the system is misregulated:– Allergies– Autoimmune disease – body loses self-tolerance– Stress/Over exertion – Immunodeficiency (bone marrow transplant)

X. Fighting Infectious Disease

• A. Infectious diseases usually affect normal function of the respiratory, circulatory & digestive systems.

• B. Most commonly used to fight disease caused by bacteria are antibiotics.– 1. Antibiotics – a chemical that slows the growth or kills

bacteria without harming human body cells

• C. Viruses are not alive so you can not kill a virus with medicine but can reduce your symptoms

IIX. Noninfectious Disease

• A. Some noninfectious diseases are inherited while others are caused by environmental factors.– 1. Ex. Cystic fibrosis, Allergies, Asthma, Diabetes &

Cancer

• B. If you have a higher risk to getting one of these diseases you should keep in mind– 1. Healthy diet, no exposure to carcinogen (sun &

smoke), early detection by doctors