Lecture 1 - Intro to The Immune System

What is the immune system?

The collection of molecules, cells, and tissues that work together in establishing immunity

What is immunity?

The state or quality of being protected from the invasion of foreign organisms or substances

What are examples of antigens?

Living microorganisms, microbial toxins/byproducts

Pollens, pet dander, chemicals

Aged, damaged, and mutant cells in the host

What are antigens?

Foreign organisms and substances

What are pathogens?

Antigens that can cause disease, typically infectious microorganisms

What are examples of cellular/living pathogens?

Parasites

Protozoa

Fungi

Prokaryote (bacteria)

What are examples of acellular/non-living pathogens?

Viruses

Prions

What are non-microbial antigens?

Antigens that can be recognized by the immune system, but do not cause disease

What are allergens?

Antigens that can cause an allergic reaction in sensitive individuals

What are examples of airborne non-microbial antigens?

Pollen

Dust mites

Pet dander

Mold and mildew

What are examples of skin transmitted non-microbial antigens?

Nickel

Latex

Fragrances

Cleaners

Cosmetics

Plants

What are examples of food transmitted non-microbial antigens?

Tree nuts/peanuts

Milk

Eggs

Soybeans

Fish/shellfish

Wheat

What are examples of medications that are considered non-microbial antigens?

Chemotherapy medicines

Sulfa drugs

Penicillin

NSAIDs

Anticonvulsants

What are the components of innate immunity?

Physical barriers

Secretions

Phagocytosis

Complement pathway

What are the 2 types of physical barriers of the innate immune system?

Strong (hair, skin, nails)

Fragile (mucosal)

What are the mechanical and chemical, barriers of the skin?

Mechanical: epithelial cells joined by tight junctions, longitudinal flow of air or fluid

Chemical: fatty acids, antimicrobial peptides

What are the mechanical and chemical barriers of the gut?

Mechanical: epithelial cells joined by tight junctions, longitudinal flow of air or fluid

Chemical: low pH, antimicrobial enzymes and peptides

What are the mechanical and chemical barriers of the lungs?

Mechanical: epithelial cells joined by tight junctions, movement of mucus by cilia

Chemical: pulmonary surfactant, antimicrobial peptides

What are the mechanical and chemical barriers of the eyes/nose/oral cavity?

Mechanical: epithelial cells joined by tight junctions, tears, nasal cilia

Chemical: antimicrobial enzymes in tears/saliva, antimicrobial peptides

What is the function of secretions?

Traps, washes off, and destroys antigens

Contain lysozymes (enzyme that kills bacteria)

Prevent bacterial colonization and growth

What are examples of secretions?

Tears

Saliva

Sweat

Gastric acid

Other body fluids

What is phagocytosis?

Uptake of pathogens by immune cells

What are the main phagocytes?

Macrophages and neutrophils

What are the 3 functions of complement?

Opsonization

Inflammation

Lysis

What is opsonization in complement?

Tags and glues bacteria to immune cells for easier phagocytosis

What is inflammation in complement?

Induces immune cell recruitment and activation

What is lysis in complement?

Directly kills bacteria by MAC formation

What are the 2 types of adaptive immunity?

Humoral immunity

Cell-mediated immunity

Humoral immunity is mediated by...

Antibodies

What are the components of humoral immunity?

B cells and plasma cells

Antibodies

What are antibodies?

Soluble proteins with specificity

Also known as immunoglobulin

Can detect and neutralize, and help eliminate specific antigens/pathogens

What are the main producers of antibodies?

Plasma cells

What are the components of cell-mediated immunity?

CD8 T cells

CD4 T cells

Antibodies anchor to the surface of __ and become __

B cells

B cell receptors (BCR)

What do B cells differentiate to and when?

After antigen recognition, B cells differentiate into plasma cells

Explain antibody specificity.

An antibody recognizes only its specific antigenic determinant

Antibody paratope is complementary to a specific antigen epitope

What is an epitope?

The specific molecular region on an antigen that is recognized and bound by the immune system (B/T cells, antibodies)

One antigen can have multiple epitopes

What is the function of antibodies?

Can neutralize bacterial toxins before they bind to their receptors on target cells

Opsonization, can coat pathogens and work with complement

What are the 3 receptors found on immune cells that allow for binding?

Antigen receptor

Antibody receptor

Complement receptor

What are the 2 types of T cells?

CD8 T cells

CD4 T cells

How are B and T cells different?

T cells cannot directly recognize pathogens, it must be presented by an MHC molecule

What are the MHC molecules for the 2 types of T cells?

CD8 T cells- MHC class 1

CD4 T cells- MHC class 2

What are alternative names for CD8 T cells?

Cytotoxic T cells (Tc)

Cytotoxic T lymphocytes (CTLs)

What are alternative names for CD4 T cells?

Helper T cells (Th)

What is the function of CD8 T cells?

Kills virus infected cells

What is the function of CD4 T cells?

Help other immune cells through recruitment/activation to clear viruses, bacteria, and parasites

Can produce cytokines

MHC class 1 binds what type of antigens?

Intracellular or endogenous antigens (viral), tumor cells

MHC class 2 binds what type of antigens?

Extracellular or exogenous antigens (bacterial, parasitic)

What are MHC molecules?

Major histocompatibility complexes

Cell surface proteins essential for the immune system to differentiate between self and non-self antigens

Is phagocytosis needed for MHC classes 1 and 2?

Not needed for MHC class 1

Needed for MHC class 2

On what cells is MHC class 1 expressed?

All nucleated cells

On what cells is MHC class 2 expressed?

Antigen-presenting cells such as macrophages, dendritic cells, and B cells

How do B and T cells rely on each other?

B cells present antigen to activate T cells

T cells produce cytokines to further activate B cells

B cells then differentiate into plasma cells

What are cytokines?

Proteins secreted by cells to regulate immune responses

Bind to specific receptors on target cells

Different cell types produce characteristic cytokines

What are examples of cytokines?

TNF (tumor necrosis factor)

IFN (interferon)

IL (interleukin)

What are the main differences between innate and adaptive immunity?

Speed

Antigen specificity

Memory

What are characteristics of innate immunity?

Rapid response within hours, first line of defense

Fixed number of antigen receptors, < 100

Limited number of specificities, only recognize patterns/groups

Constant during the course of response

What are characteristics of adaptive immunity?

Slow response in days to weeks

Variable amount of antigen receptors, > 10^9

Numerous highly selective specificities, recognize antigens individually

Improve during the course of response, has memory

What is special about toll-like receptors?

Don't initiate phagocytosis, initiate activation signaling

Macrophages can be activated and secrete cytokines

What is clonal selection in adaptive immunity?

On infection, lymphocytes with receptors that recognize the pathogen are selected, and proliferation/differentiation of selected lymphocytes occurs

Happens over 1-2 weeks