NOTES: CH 43, part 1 The Immune System - Nonspecific & Specific Defenses ( )

The lymphatic system is closely associated with the cardiovascular system.

LYMPHATIC PATHWAYS Lymphatic capillaries ● microscopic, closed-end tubes that extend into intercellular spaces ● receive LYMPH through their thin walls (LYMPH = the fluid of the lymphatic system) ● lymphatic capillary networks parallel blood capillary networks

Functions of lymph: 1) returns to the bloodstream small proteins that leaked out of blood capillaries 2) transports foreign particles, such as bacteria or viruses, to lymph nodes

**if lymph movement is impaired, it may accumulate within the intercellular spaces and produce EDEMA, or swelling (example: after surgery, the lymphatic vessels and lymph nodes around the wound may be damaged, causing fluid to accumulate around the surgery site and lead to swelling)

Lymph Nodes: Structure of a Lymph Node: ● lymph nodes are subdivided into nodules ● nodules contain masses of lymphocytes and macrophages

Locations of Lymph Nodes: ● lymph nodes aggregate in groups or chains along the paths of larger lymphatic vessels

Functions of Lymph Nodes: ● filter potentially harmful foreign particles from lymph ● are centers for the production of lymphocytes (attack invading viruses, bacteria, parasites, etc.) ● contain phagocytic cells (engulf and destroy foreign substances, damaged cells, cellular debris)

THYMUS AND SPLEEN Thymus: ● shrinks slowly after puberty ● contains large numbers of LYMPHOCYTES which mature into T CELLS (T lymphocytes) – important in providing immunity (more on these later…)

Spleen: ● largest lymphatic organ ● resembles a large lymph node (divided into lobules)

Spleen: ● spaces within splenic lobules are filled with blood ● contains many macrophages, which destroy/remove foreign particles and damaged RBCs from the blood **the spleen filters blood as the lymph nodes filter lymph!**

So, how does the body defend itself???

The body has nonspecific and specific defenses against infection / pathogens. Why don’t YOU have mold on your skin???

● PATHOGEN: a disease-causing agent; causes infection -pathogens include: virusesfungi bacteriaprotozoans

Nonspecific Defenses: ● general defense ● provide protection against many different pathogens ● involve physical and chemical barriers, fever, inflammation, phagocytosis

Specific Defenses: ● very precise ● target certain pathogens ● also known as IMMUNITY ● involve specialized lymphocytes (T cells and B cells) that recognize and respond to specific pathogens **nonspecific defenses are quick to respond; specific defenses are slower-to- respond

NONSPECIFIC DEFENSES 1) Species Resistance ● each species is resistant to certain diseases that may affect other species ● examples: measles, mumps, gonorrhea, and syphilis infect humans but not other animal species ● one species may be resistant to a disease that affects another species because its tissues somehow fail to provide a suitable environment for the pathogen (temperature, chemical environment, receptors, etc.)

2) Mechanical Barriers = FIRST LINE OF DEFENSE ● mechanical barriers / physical barriers include: -skin (and associated hairs) -mucous membranes -fluid (sweat and mucus) ● as long as they remain intact, they can keep out many pathogens

SALIVA MUCUS SKIN

**all other “nonspecific defenses” are considered the SECOND LINE OF DEFENSE

3) Chemical Barriers ● gastric juice: contains hydrochloric acid and enzymes (e.g. pepsin) that are lethal to pathogens ● tears: contain the enzyme LYSOZYME (which has antibacterial action) ● the salt in perspiration accumulates on the skin and kills bacteria on the skin

3) Chemical Barriers (cont.) INTERFERONS: chemicals released by virus-infected cells; they stimulate other immune cells to: -synthesize antiviral proteins that stimulate phagocytosis, block virus replication

Interferons: ● most effective against cold and flu virus ● now mass-produced by recombinant DNA technology to be potentially used as treatment for viral infections and cancer!

3) Chemical Barriers (cont.) COMPLEMENT SYSTEM: ● group of 30 proteins; ● catalyze a series of steps resulting in lysis of invading microbes and/or inflammatory response

4) Fever ● higher body temperature increases the rate of phagocytic cells ● also lowers iron levels in the blood (bacteria and fungi require iron, so this slows their growth)

5) Inflammation ● produces: localized redness, swelling, heat and pain ● HISTAMINE and prostaglandins released by damaged tissues attract WBCs to the site  the mass of WBCs, bacterial cells, and damaged tissue forms a thick fluid called PUS

6) Phagocytosis – removes foreign particles from the lymph and blood ● the most active phagocytes in blood are NEUTROPHILS and MONOCYTES ● Monocytes give rise to MACROPHAGES

● MACROPHAGES are found in the linings of blood vessels in the: -bone marrow -liver -spleen -lungs -lymph nodes

EOSINOPHILS: ● kill antibody-coated parasites

Specific Defenses / Immunity

Immune System… ● the body’s “third line of defense” ● characterized by:  specificity  diversity  self / non-self recognition  memory

ANTIGENS… ● ANTIGENS: specific foreign molecules that trigger an immune response; usually located on a cell’s surface -antigens include: proteinsglycoproteins polysaccharidesglycolipids

ANTIGENS… ● before birth, body cells sort “self” proteins and other large molecules ● lymphocytes develop receptors that allow them to differentiate between nonself (foreign) and self antigens ● nonself antigens combine with T cell and B cell surface receptors and stimulate these cells to cause an immune reaction

LYMPHOCYTES (T and B Cells) ● originate in the red bone marrow ● some reach the THYMUS, where they mature into T CELLS ● others, the B CELLS, mature in the RED BONE MARROW ● both T cells and B cells reside in lymphatic tissues and organs (lymph nodes, spleen, etc.)

LYMPHOCYTE FUNCTIONS **a lymphocyte must be ACTIVATED before it can respond to an antigen**

Antigen Presentation: ● Carried out by a group of approx. 20 glycoproteins that make up the MAJOR HISTOCOMPATIBILITY COMPLEX (MHC)

Two main classes of MHC molecules: ● Class I MHC: located on all nucleated body cells *cytotoxic T cells (T C ) bind to fragments of antigens displayed by class I MHC ● Class II MHC: found only on specialized cells (macrophages, B cells, activated T cells) *helper T cells (T H ) bind to fragments of antigens displayed by class II MHC

Antigen-Presenting Cells (APCs): -cells that take up antigens (B cells, macrophages); -engulfed foreign matter binds to a class II MHC molecule and is conveyed to the outside of the APC; -foreign antigen is recognized by a helper T cells (T H ); -this interaction is enhanced by CD4, a membrane protein on T H cells.

CD4

*CLONAL SELECTION:  antigen-specific selection of a lymphocyte;  activates lymphocytes to divide and differentiate to produce CLONES of effector cells & memory cells designed to eliminate the antigen that provoked the initial response SPECIFICITY & MEMORY!

PRIMARY IMMUNE RESPONSE ● PRIMARY IMMUNE RESPONSE: the first reaction / response to an antigen (first exposure)  during this response, antibodies are produced for several weeks  antibodies first show up within 5-10 days  some B cells remain dormant as MEMORY B CELLS

SECONDARY IMMUNE RESPONSE ● SECONDARY IMMUNE RESPONSE: the second response (exposure) to an antigen  rapid response due to memory cells produced during the first exposure  antibodies produced within a day or two