Immune Response

1. Third line of defense
• called immune response
• specific to particular pathogen
• allows immune system to "remember" pathogen after infection
• immune system can launch faster and stronger attack if affected again
• mainly involves lymphatic system
2. Lymphatic system (in detail) 
• three basic functions
• absorbs fatty acids after digestion of lipids in small intestine then transports fatty acids throughout bloodstream, and circulate throughout the body 
• removes excess fluid from body tissues and returns fluid to blood, filtered of pathogens
• produce lymphocytes, which are the type of white blood cells that are primarily involved in the immune response
3. Organs of lymphatic system
• red bone marrow
• produces leukocytes
• thymus
• gland located in upper chest behind breast bone
• stores and matures lymphocytes
• spleen
• gland in upper abdomen
• filters blood and destroys worn-out red blood cells
• destroys any pathogens filtered out of the blood
• tonsils
• glands on either side of the pharynx
• trap pathogens, which are destroyed by lymphocytes in tonsils
4. Lymphatic system (continued) 
• lymphatic vessels make up body-wide circulation system
• circulates lymph instead of blood
• lymphatic system does not need to pump to force lymph through vessels
• lymph circulates because of peristalsis of lymphatic vessels and rhythmic contraction of skeletal muscles
• valves prevents lymph from flowing bakwards
• lymph accumulates between cells, diffusing into lymphatic vessels, and moves through lymphatic system until it reaches the main lymphatic ducts in chest
• drains into bloodstream
• pathogens filtered at lymph nodes
• small, oval structures that act like filters
5. Lymphocytes
• key cells involved in immune response
• estimated two trillion lymphocytes in human body
• B lymphocytes (B cells) and T lymphocytes (T cells) 
• both produced in red bone marrow
• B cells mature in bone red marrow
• T cells mature in thymus
• both can recognize and respond to specific pathogens
6. Antigens
• B cells and T cells respond to antigens on pathogens, and not the pathogens themselves
• can "recognize" specific antigens because they have receptor molecules on surface
• fit between receptor molecule and specific antigen is like lock and key
• receptors on B and T cells recognize and bind to one type of antigen
7. Humoral immune response
• B cells responsible for humoral immune response
• takes place in blood and lymph and involves production of antibodies
• immunoglobins
8. B cell Activation
• Naïve B cells (unactivated B cells) are activated by an antigen
• B cell encounters matching antigen, and engulfs it
• displays fragments of antigen on surface
• helper T cells come to help bind B cells at antigen site and release cytokines
• help stimulate B cells to develop into plasma cells or memory cells
9. Plasma cells and antibody production
• plasma cells: activated B cells that secrete antibodies
• specialized to act like antibody factories
• antibodies produced by plasma cells circulate in blood and lymph
• each antibody binds to one antigen
• depends on plasma cell that produced it
• antigen-antibody complex
• flags a pathogen or foreign cell for destruction by phagocytosis
• liver removes antigen-antibody complexes from blood
• spleen removes it from lymph
10. Memory cells
• live much longer than plasma cells
• are activated B (or T) cells that retain memory of a specific pathogen after an infection
• helps launch rapid response against pathogen in the future
• remain in lymph
11. T cell activation
• B cells or macrophages engulf pathogens and display parts of the pathogen's antigen on surface
• antigen-presenting cell
• naïve T cells encounters matching antigen, and begins activation process
• different T cells play roles in immune response
12. Helper T cells
• do not kill pathogens or destroy infected cells
• necessary for immune response
• "managers" of immune response
• divide rapidly and secrete cytokines after activation
• cytokines from helper T cells help activate B cells and other T cells
• most helper T cells die out after pathogen has been cleared
• some remain in lymph as memory cells
• ready to produce large numbers of antigen-specific helper T cells if pathogen attacks again
13. Cytotoxic T cells
• destroys tumor cells, damaged cells, and infected cells once activated
• involved in rejection of transplanted organs
• divides rapidly to produce "army" of identical cells
• when they find antigen-carrying pathogens, it releases toxins that form pores in cell's membrane
• cell bursts, destroying the cell and virus inside of it
• most die off after viral infection is under control
• some also remain as memory cells
14. Regulatory T cells
• shut down cell-mediated immunity at the end of an immune response
15. Active immunity
• immunity that results rom pathogen stimulating immune response
• leaves you with memory cells for specific pathogen
• pathogen is unlikely to re-infect you and make you sick again
• some memory cells can last for a lifetime
• also can occur through immunization
• deliberate exposure of a person to pathogen to provoke immune response
• to prevent actual infections by pathogen
• pathogen typically injected
• weakened form is used to provoke immune response yet not actually infect
• immunized: measles, mumps, rubella, whooping cough, and chicken pox
16. Passive immunity
• humoral immunity that ends after a few days