Immune System Immune System Overview Influenza Infection phagocytic leukocyte

Immune Systems Highly developed in mammals Two types of immunity: Innate immunity (nonspecific) Acquired immunity (specific) What about other organisms? Lymphatic System: Production & transport of leukocytes (WBC) Traps foreign invaders

Bacteria & insects inherit resistance. Vertebrates acquire immunity. Lines of defense 1st line: Non-specific barriers broad, external defense “walls & moats” skin & mucous membranes 2nd line: Non-specific patrols broad, internal defense “patrolling soldiers” leukocytes = phagocytic WBC 3rd line: True immune system specific, acquired immunity “elite trained units” lymphocytes & antibodies B cells & T cells Bacteria & insects inherit resistance. Vertebrates acquire immunity.

1st line: Non-specific External defense Barrier skin Traps mucous membranes, cilia, hair, earwax Elimination coughing, sneezing, urination, diarrhea Unfavorable pH stomach acid, sweat, saliva, urine Lysozyme enzyme digests bacterial cell walls tears, sweat Lining of trachea: ciliated cells & mucus secreting cells

2nd line: Non-specific patrolling cells bacteria attack pathogens, but don’t “remember” for next time leukocytes phagocytic white blood cells macrophages, neutrophils, natural killer cells, dendritic cells Antimicrobial proteins Complement system Interferons inflammatory response increase in body temp. increase capillary permeability attract macrophages/neutrophils macrophage yeast

Inflammatory response Histamine and cytokines increase blood flow to damaged site, making it look red and puffy = INFLAMMED!

3rd line: Acquired (active) Immunity Specific defense with memory lymphocytes B cells - humoral response T cells – cell mediated response They respond to… Antigens! B cell

B cells Involved in HUMORAL RESPONSE Attacks foreign antigens in blood or lymph Produce specific antibodies against specific antigens Types of B cells plasma cells immediate production of antibodies rapid response, short term release memory cells continued circulation in body long term immunity

How are invaders recognized? Antigens - cellular name tag proteins “self” antigens no response from WBCs Major Histocompatibility Complex – MHC Protein used by all cells for recognition “foreign” antigens response from WBCs pathogens: viruses, bacteria, protozoa, parasitic worms, fungi, toxins non-pathogens: cancer cells, transplanted tissue, pollen Mature lymphocytes are tested to make sure they can distinguish self vs. non-self “self” “foreign”

Humoral Immune Response In the diagram above a B cell is being activated by a T helper cell. This B cell will make plasma cells and memory B cells that will secrete antibodies to fight the current and future infections.

What do antibodies do to invaders? Antibodies in Action

T cells Involved in CELL MEDIATED RESPONSE Attack, learn & remember pathogens hiding in infected cells recognize antigen fragments also defend against “non-self” body cells cancer & transplant cells Types of T cells helper T cells alerts rest of immune system cytotoxic (killer) T cells attack infected body cells memory T cells long term immunity T cell attacking cancer cell

How do T cells know a cell is infected? Infected cells digest some pathogens Class I MHC proteins carry pieces of foreign cell to surface foreign antigens now on cell membrane called Antigen Presenting Cell (APC) Helper T cell becomes active

Cell-Mediated Response Activation of Helper T cell results in activation of Cytotoxic T cells (as well as B cells) Cytotoxic T cells destroy infected body cells or cancer cells (look for Class I MHC) Cytotoxic (killer) T cells secrete perforin protein causing apoptosis or lysis of infected cell

Active Immunity Get exposed to pathogen! Naturally – get sick Artificially – get a vaccination Both methods cause memory cells to be made for future exposures. Rapid response to second exposure. You don’t even know you were exposed!

Passive immunity (antibodies not immune cells) Naturally Obtaining antibodies from mother antibodies pass from mother to baby across placenta or in mother’s milk critical role of breastfeeding in infant health Artificially injection of antibodies Ex: anti-venom serum short-term immunity

HIV & AIDS Human Immunodeficiency Virus virus infects helper T cells AIDS: Acquired ImmunoDeficiency Syndrome infections and death by opportunistic diseases pneumonia, cancers HIV infected T cell

Immune system malfunctions Auto-immune diseases immune system attacks own molecules & cells rheumatoid arthritis Diabetes multiple sclerosis Allergies makes wrong antibody for foreign antigen allergens = proteins on pollen, dust mites, in animal saliva 1st exposure you are not allergic. Allergy is confirmed after subsequent exposures