Body Defenses: The Immune System
The body is constantly in contact with protists, bacteria, fungi, and viruses
The body has two defense systems for foreign materials
Innate defense system (nonspecific defense system)
Mechanisms protect against a variety of invaders
Responds immediately to protect body from foreign materials
Adaptive defense system (specific defense system) is a specific defense is required for each type
We can develop immunity or specific resistance to certain pathogens
Innate (Nonspecific) body defenses: First line defense
Skin is a physical barrier to foreign materials
mucus traps microorganisms in digestive and respiratory pathways.
Secretions from sebaceous and sweat glands (salty sweat), sebum is toxic to bacteria
Sebaceous glands secrete oily substances into hair follicles
Vaginal secretions are acidic
pH of the skin is acidic to inhibit bacterial growth
Stomach Mucosa and secrete hydrochloric acid, also has protein-digesting enzymes Hydrochloric acid can also kill a lot of pathogens that exist or might exist on the food
Certain pathogens are dormant until they stay in contact with hydrochloric acid.
Red Queen Hypothesis: Both pathogens and hosts are constantly evolving so they have the best
chance of the survival
Immune system is the driving force behind evolution
Lysozymes in tears, sweat, saliva, etc can break down bacteria.
Nonspecific immune System’s general Response: Flu-like Symptoms
Body’s generic response
Makes the body’s environment uncomfortable or inhospitable
Runny nose and watery eyes
Mucus flushes out pathogens
Fluid and mucus in lungs
Flushes out pathogens
Flushes out pathogens
More of an alert system
More of an alert system
Innate (nonspecific) body defenses: Second line of defense Fever
Abnormally high body temperature
Hypothalamus heat regulation can be reset by pyrogens (secreted by white blood cells)
Apyrogen is substance than can cause fever
High temperatures inhibit the release of iron and zinc from the liver and spleen needed by
Fever also increases the speed of tissue repair.
Heat increases the density of sticky molecules on the surface of blood vessels in the lymph
nodes, which catch more white blood cells as the blood rushes past.
Innate (nonspecific body Defense: Second Line of Defense: Phagocytosis
Phagocytosis is a process
Neutrophils move by diapedesis (movement of blood cells through capillary walls) to clean up
damaged tissue and/or pathogens
Monocytes become macrophages and complete disposal of cell debris
Phagoctyes are a cell type
Cells such as neutrophils and macrophages engulf foreign material into a vacuole.
Enzymes from lysosomes digest the material.
Innate (Nonspecific) Body Defenses: Second Line of Defense: Natural Killer Cells
Natural Killers (NK) cells
Can lyse (disintegrate or dissolve) and kill cancer cells
Can destroy virus-infected cells
Innate (Nonspecific) Body Defenses: Second line of defense: Inflammation
Functions of the inflammatory response
Prevents the spread of damaging agents Disposes of cell debris and pathogens through phagocytosis.
Sets the stage for repair
Triggered when body tissues are injured
Series of events causing accumulation of proteins, fluids, and phagocytosis
Four most common indications of acute inflammation
Results in a chain of events leading to protection and healing.
Pain modifies and alters behaviors
Pain responses are temporarily delayed.
Reflex to move away from pain is faster than the understanding that there is pain
Innate (Nonspecific) Body defenses: Second line of Defense: antimicrobial proteins
Hinder reproduction of microorganisms
Most important antimicrobial proteins
Complement proteins Uses a MAC (membrane attack complex) proteins to lyse cells
May be part of the specific (adaptive) or nonspecific (innate) immune response.
Proteins secreted by virus-infected cells
Bind to healthy cell surfaces to interfere with the ability of viruses to multiply.
Stops protein synthesis.
Second Line of defense: Complement system: plasma proteins that lyse foreign cells, especially
Response involves ~ 30 proteins in cascade resulting in MAC on surface of bacteria
MAC pierces bacterial membrane causing lysis
Triggers histamine release from mast cell
May act as opsonins (working with antibodies)
Binding to carbohydrates on bacterial cell walls
Part of nonspecific defense mechanisms.
Binding to antibodies attached to bacteria
Part of specific defense mechanisms
Specific (Adaptive) Immune responses: Third line of Defense
Specific immune responses trigged by foreign matter reaching lymphoid tissue
Antibodies are proteins that protect from pathogens
Aspects of Adaptive defense Antigen specific, recognizes and acts against particular foreign substances
Systemic, not restricted to the initial infection site
Memory, recognizes and mounts to a stronger attack on previously encountered pathogens
Can recognize self from non-self
Specific (Adaptive) Immune Responses: Third Line of Defense
Types of Immunity
Humoral immunity is antibody – mediated immunity is B cell mediated
Humors – refers to the fluid in the body
Provided by antibodies present in body fluids
Involves secretion of antibodies by plasma cells
Defense against bacteria. toxins, viruses in body fluids
Cellular immunity – T cell-mediated immunity
Targets Virus-infected cells, cancer cells, and cells of foreign grafts
Involves lysis of cells by cytotoxic T cells
Defend against bacteria, viruses in body cells
Part of reaction to transplant and cancer cell
Macrophages present to the Helper T cells the nametag of the Bacterial Cells
Specific (Adaptive) Immune Responses Third Line of Defense
Antigens (nonself are very specific)
Any Substance capable of exciting the immune system and provoking an immune response Antigens
Part of foreign invader, tumor cell
Epitopes – recognition sites on pathogen/antigen for B or T cells.
B cell and T cell specificity
Antigens recognize certain antigens only
B cells – membrane antibodies
T cells – T cell receptors
Human cells have many surface proteins
Our immune cells do not attack our own proteins
Our cells in another person’s body can trigger an immune response because they are foreign and
restricts donors for transplants.
Specific (Adaptive) Immune Responses: Third line of defense
Immunocompetent – cell becomes capable of responding to a specific antigen by binding to it
Cells of theAdaptive Defense system
Originate from hemocytoblasts in the red bone marrow
B lymphocytes become immunecompetent in the bone marrow (remember B for Bone Marrow)
T lymphocytes become immunocompetent in the thymus (remember T for Thymus)
Arises from monocytes Become widely distributed in lymphoid organs
Secrete cytokines (proteins important in the immune response)
B and T cells do not attack normal cells od body
As cells develop in bone marrow and thymus, any that have antigen receptors against normal
body cells are destroyed by apoptosis (programmed cell death)
Autoimmune diseases caused by failure of self-tolerance
MHC molecules unique to individual person
Major histocompatibility complex – MHC
MHC marks body cells as self
Responsible for tissue/organ rejection – stimulates immune response to foreign tissue.
Specific (adaptive) Immune Responses: Third line of Defense: T cells and Cellular Immunity
T cells defense against foreign or abnormal matter through direct contact
T Cell Clones
Cytotoxic (killer) T cells
Specialize in killing infected cells
Insert a toxic chemicals (perforin/Fragmentin)
Helper T cells
Recruit other cells fight to the invaders
Interacts directly with B cells
Regulatory (suppressor T cells)