Lecture 15 & 16 : Immunity Flashcards
What is immunity and what types are their?
Immunity is the body’s ability to defend itself against infectious agents, foreign cells and abnormal body cells.
- innate and adaptive immunity
What is innate immunity?
- first line of defence
- present before exposure to pathogen & effective from birth
- nonspecific,quick recognition and response to variety of microbes
What is adaptive immunity?
- the second line of defense
- activated after exposure to pathogens
- pathogen specific
- retains memory
What are the external and internal defenses of non-specific innate immunity?
External defenses:
- barriers to entry
Internal defenses:
- inflammatory reaction
- phagocytic and natural killer cells
- protective proteins
Explain how the skin and mucous membrane are barriers to entry:
- Intact skin cannot be penetrated by viruses or bacteria except for small cuts
- the mucous membrane lining the digestive, respiratory and genitourinary tracts prevent entry of harmful microbes, with some cells secreting mucus, a fluid that traps microbes and particles.
How does washing action and secretions act as barriers?
- the washing action of saliva, tears and urine inhibit infection by microbes
- secretions from sebaceous (oil) glands and sweat glands give the skin a 3-5 pH range, acidic enough to kill certain bacteria and prevent colonization by bacteria
How does the stomach and upper respiratory tract as barriers? What else is a barrier?
- the URS is limed by ciliated cells that sweep mucus and trapped particles or microbes up into the throat, where they can be swallowed or coughed out.
- the acidic environment of the stomach destroys most pathogens before they enter the intestines
- harmless bacteria (normal flora) in the intestine also prevent colonization by pathogens
what are the internal innate defenses and when are they activated?
- when external innate defenses fail, internal innate defences are activated
- inflammatory reaction
- phagocytic cell
- natural killer cells
- protective proteins
How does an inflammatory reaction work?
- characterized by redness, heat, swelling and pain.
- mast cells release inflammatory chemicals (histamine and kinky) that dilate capillaries bringing blood to the site
- inc. permeability allows protein and fluids to escape into the tissue, causing swelling
- swollen area and kinins stimulate free nerve endings, causing pain
How do phagocytes work?
- phagocytes attach to microbes and engulf them by endocytosis
- a vacuole is formed, fusing with a lysosome
- the lysosome kills microbes by producing nitric oxide and free radicals (toxic) that degrade them into smaller fragments
- the degraded products are secreted out by exocytosis
How do Natural Killer cells work?
- NK cells patrol the body and attack virus infected cells and cancer cells
- stress-induced molecules are produced and are put on the surface of these cells
- NK receptor (killer activating receptor) recognized these stress induced molecules
- a positive signal is sent to enable the NK cell to kill the bound cell
How do protective proteins work?
Lysozymes: present in saliva, tears and mucous secretions can destroy bacteria
Interferons ( a and b ) : produced by virus infected cells to protect non-infected cells (used to treat certain viral infections such as hepatitis C)
What is the complement system?
- 30 proteins in plasma, that are activated by bacterial infections ( C5b) to participate in the inflammatory response by attracting phagocytes to the site of inflammation
- some complement proteins (C3b) bind to surface of pathogens and help the phagocytosis of the pathogen by macrophages and neutrophils
- other complement proteins (c5-c9) join to form a membrane attack complex that makes holes in the cell walls and plasma membranes of bacteria
When is adaptive immunity activated ?
It is activated when innate immunity (external and internal) have failed to prevent an infection & consists of lymphocytes.
What is an antigen?
- Antigen : any foreign molecule that is recognized by lymphocytes and induces a response from them
- most antigens are large molecules ( proteins and polysaccharides )
- the immune system is able to differentiate from self and non-self (antigens)
What is the role of Lymphocytes in adaptive immunity?
- lymphocytes recognize antigens through antigen receptors attached to their plasma membrane
- so adaptive immunity thus requires this recognition of antigens by lymphocytes
What occurs when lymphocytes interact with antigens?
- a specific defense, either a humoral immune response or a cellular immune response
What is humoral immunity?
- B lymphocytes (from bone marrow) recognize antigens
- undergo activation and proliferation (mitosis) and differentiate to become plasma and memory cells
- plasma cells secrete antibodies for extra cellular pathogens
- called humoral due to presence of antibodies in body fluids (humor)
What are antibodies?
- a glycolic protein produced in response to an antigen and binds with it via non-covalent interactions
- antibodies are also known as immunoglobulins
- 5 types : igM,igG,igG,igE and igD
What is the structure of an antibody?
- Y shaped with two arms
- each arm has a heavy long polypeptide chain and a light short polypeptide chain with variable and constant regions.
- the antigen combines with the antibody at the antigen bonding site in and a lock and key manner and forms antigen-antibody complexes.
What are the functions of an antibody?
- neutralize viruses and bacteria
- agglutinate bacteria (clump)
- inactivate toxins and soluble antigens
- facilitate uptake of pathogen and soluble antigens by phagocytic cells
- activate the complement system to kill the pathogen
What is cell mediated immunity and what does it give rise to?
- CMI is mediated by T-cells (produced in bone marrow and mature in thymus)
- involves activation and colonial selection of T cells resulting in helper, cytotoxic and memory T cells.
What is the process of CMI?
- T cells recognize antigens on surface of antigen presenting cells (APC) through T cell receptor, with help from self proteins ( major histocompatibility complex molecules )
- after recognition, helper T cells are activated and secrete cytokines that stimulate other cells
What do these cytokines stimulate?
- helper T cells for proliferation by cell division
- B cells to proliferate and differentiate into plasma cells to secrete antibodies
- cytotoxic cells to proliferate and kill virus infected cells and cancer cells
- macrophages and neutrophils to kill intracellular pathogens
