Lecture #6: Immunity Flashcards
What are pathogens?
Disease causing agents
What do immue systems do?
- recognize foreign cells
- destory pathogens
- produce immue cells and proteins
What are the 2 types of immunity?
Innate immunity and adaptive immunity
Innate immunity
- present in all animals from time of birth
- an immediate defense upon infection
- responds to broad range of pathogens; non-specific
Adaptive immunity
- Present in vertebrates
- develops after exposure to agents such as microbes, toxins, or other foreign substances
- involves a very SPECIFIC response to pathogens
Invertebrates
They have INNATE IMMUNITY
- exoskeleton of insects serves as barrier (chitin) to entry
- lysozyme = enzyme that breaks down bacteria cell walls
- itemocytes = cells circulating within hemolyph that carry out phagocytosis
- immue cells recognize bacteria and fungi by structures on their cell walls
- various classes of pathogens elict immune response
What is phagocytosis?
Ingestion and digestion of foreign substances including bacteria
Vertebrates
THEY HAVE ADAPTIVE IMMUNITY
- Barrier defenses, phagocytosis, antimicrobial peptides (similar to invertebrates)
- Natural killer cells, interferons, inflammatory response (unique to vertebrates)
Barrier defenses
- skin and mucous membranes of respiatory, urinary, and reproductive tracts are physical barriers
- mucus traps and allows for the removal of microbes (cilia of respiatory tract)
- many body fluids including saliva, mucus, and tears are hostile to many microbes (lysozomes in respiatory tract and tears)
- The low ph of skin (oil gland secretion) and the digestive system (acidic ph of stomach) prevents growth of many bacteria
Cellular innate defenses
- groups of pathogens are recognized by receptors on phagocytic cells
- these receptors recognize fragments of molecules characteristic of a set of pathogens
What are the two main phagocytic cells?
- macrophages
- neutrophils
What do dendritic cells do?
Stimulates the development of adaptive immunity
- eosinophils discharge destructive enzymes, peptides, and proteins
What do peptides and proteins do?
attack pathogens or stop their reproduction
Interferon proteins
produced by virally-infected cells warning noninfected cells and activating macrophages
Complement system
Consists of about 30 plasma proteins which cause lysis (poke holes) of invading cells
- helps trigger inflammation by attracting phagocytes to the scene
Inflammatory response
- mast cells (a type of connective tissue) release histamine which triggers blood vessels to dilate and become more permeable
- activated macrophages and neutrophils release cytokines, signaling molecules that enhance the immune response
- enhanced blood flow to site helps deliver antimicrobial peptides that result in an accumulation of pus (fluid rich in white blood cells, dead pathogens, and cell debris from damaged tissues)
Inflamation is either…
local: redness, heat, swelling/edema, pain
systemic: throughout the body
- fever is a systemic inflammatory response triggered by pyrogens released by macrophages in response to certain pathogens
- inhibits microbial growth
- speeds up phagocytosis and tissue repair
septic shock
life threatening condition caused by overwhelming inflammatory response
What does adaptive immunity rely on?
Two types of lymphocytes (type of white blood cell)
- T cells
- B cells
T cells
Mature in the thymus
B cells
Mature in bone marrow
Antigens
substances that can elict a response from a B cell or a T cell
- B cells and T cells bind to antigens via antigen receptors which are specific to part of one molecule of that pathogen
- each individual B or T cell is specialized to recognize a specific type of molecule
epitope
small, accessible part of antigen that binds to antigen receptor
Antigen recognition by B cells and antibodies
- each b cell antigen receptor is a y-shaped molecule with two identical heavy chains and two identical light chains
- constant regions vary little, variable regions differ greatly
- variable regions provide antigen specificity
Antigen recognition by T cells
- T cell receptors have two different polypeptide chains (called α and β)
- Tips of the chain form a variable (v) region, the rest is a constant (c) region
- Bind to antigen fragments displayed/presented on host cell
What are the 4 characteristics of the adaptive immune system?
- immense diversity of lymphocytes and receptors
- self- tolerance (lack of reactivity against an animal’s own molecules)
- B + T cells proliferate after activation
- Immunological memory
Immunological memory
- responsible for long-term protections against diseases
Primary immune response
first exposure to a specific antigen
Secondary immune response
memory cells facilitate a faster, more effective response
Humoral immune response
antibodies help neutralize or eliminate toxins and pathogens in the blood and lymph (b cells)
Cell-mediated immune response
specialized T cells destroy affected host cells (cytotoxic T cells)
Helper T cells
type of T cells that triggers both the humoral and cell-mediated immune responses
Allergies
exaggerated (hypersensitive) responses to antigens called allergens
Autoimmune diseases
the immune system loses tolerance for self, and turns against certain molecules of the body
Examples of autoimmune diseases
- Systemic lupus
- erythematosus
- rheumatoid arthritis
- insulin-dependent diabetes mellitus
- multiple sclerosis
