Nonspecific Defense Against Disease

Section 33.2

Intro• Constant exposure to pathogens

• Warm bodies of humans make an ideal place for pathogens to nest

• Nonspecific defense: first line of defense

• Innate immunity: no recognition of an intruder that has attacked before

• Human immune system is the most studied

Immunity

• Nonspecific defenses in immunity include:

• Barriers to entry (skin)

• Protective proteins

• Phagocytes

• The inflammatory response

Barriers to Entry• Non chemical and

mechanical barriers: skin and mucous membranes

• Ex. Dead cells form impermeable layer on skin

• Skin: once injured, there is possibility of infection

Barriers to Entry

•Mucous of the mucous membranes trap microbes

•Mucous membranes secrete lysozyme (enzyme that disintegrates bacteria)

•Microbes: bacterium causing disease or fermentation

•Role of upper respiratory tract: ciliated cells sweep up mucous and particles into the throat

•Regular bacteria residing in intestines also block pathogens

• Oil glands: contain chemicals that can weaken or kill bacteria on the skin

•Role of acidic pH in the stomach prevents growth of bacteria

Inflammatory Response

• Inflammatory response: series of events that follows tissue damage by pathogens

• Signs of an inflamed area: redness, heat, swelling and pain

• Redness and heat is caused by excess blood flow

• Damaged tissue cells release the chemical mediator, histamine (capillaries dilate, increases blood flow)

• Swollen area stimulates nerve endings, resulting in pain

• Phagocytes (neutrophils and monocytes) squeeze through capillary walls, enter tissue fluid, ingest pathogens and release cytokines (stimulate inflammation)

Inflammatory Response

• Most responses are done by dendritic cells, which devour pathogens and are able to survive

• Cytokines (released by macrophages) stimulate the production and release of white blood cells (neutrophils)

• Formation of pus: whitish material composed of dead tissue cells and dead bacteria

• Presence of pus indicates the body trying to overcome and infection

• Other responses: formation of blood clots which prevent blood loss in capillaries

• Chronic inflammation: persisting inflammation, controlled by agents such as aspirin or cortisone

Video

http://www.youtube.com/watch?v=Ue6Yym25NWc

Role of the Fever

• Fever: elevated body temperature

• Controversy of fever treatment

• Fever can be responsible for providing an unfavorable environment for invader

• Increasing body temperature in mice decreased death rate, shortened recovery time for infections

• Fever can also limit the growth of tumor cells

• Conclusion? An extreme fever should be treated, but mild cases should be left alone

Phagocytes Role in Defense

• Most white blood cells are phagocytes

• Neutrophils: cells that leave the bloodstream and engulf bacteria in tissue

• Eosinophils: phagocytic cells which mount attacks against animal parasites

• Two most powerful phagocytic white blood cells: macrophages and dendritic cells

• Dendritic cells: found in skin, devour pathogens and stimulate natural killer cells (lymphocytes)

• Macrophages: found in tissues, stimulate lymphocytes to carry on specific immunity

Natural Killer (NK) Cells

• Large lymphocytes that kill virus infected cells and cancer cells through cell-to-cell contact

• Produce cytokines that promote specific defenses

• NK cells congregate in the tonsils, lymph nodes, and the spleen (stimulated by dendritic cells)

• NK cells look for a self-protein on the body's cells

• If a cancer cell has lost it's self-proteins, the NK cell will kill it through the use of T cells

• NK cells are not specific, and therefore have no memory

Protective Proteins• Complement: blood plasma

proteins that "compliment" immune responses

• Located in blood plasma, but must be activated by pathogens

• Can create holes that allow fluid or salt to enter until the cell bursts

Protective Proteins

Complement proteins help destroy pathogens by:

•Enhanced inflammation-certain proteins can bind to mast cells (white blood cell) and trigger histamine

•Binding to surface of pathogens that are already covered with antibodies

•Form a membrane attack complex that provides holes in the surface or bacteria and viruses

•Interferons (cytokines) are soluble proteins that affect behavior of other cells

•Interferons bind to the receptors of non infected cells, producing substances that interfere with viral replication