UNIT 2: IMMUNE SYSTEMS(Campbell & Reece, 2010 –Chapter 43,
INTRODUCTION TO IMMUNITY• An immune system is a system of• biological structures and• processes within an organism• that protects against disease.• In order to function properly, animmune system must detect a widevariety of agents, from viruses toparasitic worms, and distinguish themfrom the organisms own healthytissue.
COUNTER ACTION OF THESE AGENTSThese agents are referred to aspathogens – an organism or substancethat could cause a disease.Pathogens can rapidly evolve and adaptto avoid detection and destruction bythe immune system.As a result, multiple defencemechanisms have also evolved torecognize and neutralize pathogens.
Physical barriers prevent pathogenssuch as bacteria and viruses fromentering the organism.If a pathogen breaches thesebarriers, the innate immune systemprovides an immediate, but non-specific response.Innate immune systems are found in allplants and animals.
If pathogens successfully evade theinnate response, vertebrates possess asecond layer of protection, the acquiredimmune system,which is activated by the innateresponse.Here, the immune system adapts itsresponse during an infection to improveits recognition of the pathogen.This improved response is then retainedafter the pathogen has been eliminated, inthe form of an immunological memory,and allows the acquired immune system tomount faster and stronger attacks eachtime this pathogen is encountered.
Differences in the components of theimmune systemInnate immune system Acquired immune systemResponse is non-specificPathogen and antigenspecific responseExposure leads toimmediate maximalresponseLag time between exposureand maximal responseCell-mediated andhumoral componentsCell-mediated and humoralcomponentsNo immunologicalmemoryExposure leads toimmunological memoryFound in nearly allforms of lifeFound only in jawedvertebrates
2. INNATE IMMUNITYInnate immune responses are activeimmediately upon infection and are thesame whether or not the pathogen hasbeen encountered previously.It includes barrier defensesand internal defenses
Mucus membranesSome cells in mucus membraneproduce mucus.Mucus is a viscous fluid thatenhances defences – trappingmicrobes and other foreignparticles
In the trachea, ciliatedepithelial cells sweep mucusand the trapped microbesupwards, helping to preventinfection of the lungs. mucus
Body secretions create anenvironment that inunfavourable for microbes.Lysozymes in saliva, mucoussecretions, and tears destroysusceptible bacteria as theyenter the respiratory tract oropenings around eyes.Acid in stomach kill bacteriaOils and sweat give human skina pH between 3-5, which is acidicenough to prevent the growth ofmicroorganisms.
INTERNAL DEFENSEIf the barrier defences aredamaged and pathogens do enterthe body of an organism, a secondline of defence will be activated.This defence system is theinternal defence system and ismore sensitive and includes:phagocytosis and inflammation.
PHAGOCYTOSISProcess by which certain livingcells called phagocytes ingest orengulf other cells or particles.The phagocyte may be a one-celled organism, such as anamoeba, or one of the bodycells, such as a leukocyte (whiteblood cell). In higher animals phagocytosisis chiefly a defensive reactionagainst infection and invasion ofthe body
Different types of phagocyticcells:Neutrophils engulf and destroymicrobesMacrophages are part of thelymphatic system and are foundthroughout the bodyEosinophils discharge destructiveenzymesDendritic cells stimulatedevelopment of acquired immunity
INFLAMMATORY RESPONSESWhen injured or infected bypathogens, signalling moleculesare released,One example of a signallingmolecules is histamine – stored inmast cells.These molecules trigger the bloodvessels to dilate and becomemore permeable
This increase local blood supply andallow more phagocytes andantimicrobial proteins to entertissuesPus, a fluid rich in white blood cells,dead microbes, and cell debris,accumulates at the site of inflammationFever is a systemic inflammatoryresponse triggered by pyrogensreleased by macrophages, and toxinsfrom pathogens
MAJOR EVENTS IN A LOCALINFLAMMATORY RESPONSEActivatedmacrophagesand mast cellsat the injury sitereleasesignallingmolecules thatact on nearbycapillaries.
The capillaries dilate andbecome morepermeable, allowingfluid containingantimibrobial peptidesto enter the tissue.Signaling moleculesreleased by immune cellsattract additionalphagocytic cells.
Phagocytic cellsdigest pathogens andcell debris at thesite, and the tissueheals
ACQUIRED IMMUNITYAcquired immunity is a specific immuneresponse system through which thebody specifically detects and destroysparticular substances. This immunity protects us againstinfectious diseases as the body haslearnt to recognize foreign substances. It produces a specific reaction to eachinfectious agent, eradicating that agentfrom the body.
This ability to recognize a pathogenthat has previously elicited an immuneresponse is the basis for acquiringimmunity to specific diseases.Hence, we suffer from manydiseases, such as chicken pox, measlesetc. only once.Thus we can summarize: Acquiredimmunity involves 2 main activities:Destruction of the invadersMemory of this response
WHICH CELLS ARE INVOLVED INACQUIRED IMMUNITY RESPONSE?Special leucocytes, called thelymphocytes are released from thebone marrow.Some reach the Thymus gland andmature to form T-lymphocytes (T-cells)Some become B-lymphocytes (B-cells) and is present in the bonemarrow and lymph nodes)
HOW B-LYMPHOCYTES WORKantibodyB-lymphocytesoThe B-lymphocyte form antibodieso One type of B-lymphocyte is activated bya specific antigen on the surface of aforeign body
The antibodies bond to the antigensand destroy the foreign body.
ACTIVE ACQUIRED IMMUNITYActive immunity occurs when aperson has already been exposedto antigens (from pathogens)And develops a secondary responseagainst specific pathogens.People receive vaccinations todevelop a primary response, andthen if they get the pathogens later,active immunity helps to fightthem off.
Antigens are foreign molecules,found on the surface of pathogens,each pathogen has a specific antigen. The immunity system has countlessamounts of B-Lymphocytes.Each B-lymphocyte is able torecognize a specific antigen.The B-lymphocytes then produceantibodies that will bond to theantigens.This will neutralize or destroy thepathogen.
PASSIVE IMMUNITYIn natural passive immunity, antibodies arepassed from a mother to a child.Antibodies can be transferred through theplacenta, or transmitted through the colostrum.The antibodies transmitted through thecolostrum and placenta generally only last forseveral weeks, which is long enough to allowthe baby to start to build up its own immunesystem and to make its own antibodies.Artificial passive immunity involves theintroduction of antibodies through means suchas injection - VACCINATIONS.
HUMORAL VS. CELL MEDIATEDIMMUNITYHumoral immunity - deals with infectiousagents in the blood and body tissuesCell-mediated immunity - deals with bodycells that have been infected.In general, the humoral system is managedby B-cells (with help from T-cells).The cell-mediated system is managed by T-cells.
VACCINATIONSAll vaccinations work by presentinga foreign antigen to the immunesystem in order to evoke animmune response, but there areseveral ways to do this.We will look at 4 methods:
1. Using an inactivated vaccineAn inactivated vaccine consists ofvirus or bacteria that are grown inculture and then killed .Although the virus or bacteria particlesare destroyed and cannot replicate, thevirus capsid proteins or bacterial wallare intact enough to be recognizedand remembered by the immunesystem. This evokes an immune response.
2. Using an attenuated vaccineIn an attenuated vaccine, live virusor bacteria with very low virulence areadministered.They will replicate, but locally or veryslowly.Which causes an immune response toproduce antibodies.
3. Virus-like particle vaccinesVirus-like particle vaccines consist ofviral protein(s) derived from thestructural proteins of a virus. These proteins can self-assemble intoparticles that resemble the virus fromwhich they were derived but lack viralnucleic acid, meaning that they are notinfectious.The human papillomavirus and HepatitisB virus vaccines are two virus-likeparticle-based vaccines currently inclinical use.
4. A subunit vaccineA subunit vaccine presents anantigen to the immune systemwithout introducing viral particles.One method of production involvesisolation of a specific protein from avirus or bacterium and administeringthis by itself.
ANTIBIOTICSAntibiotics are also known as anti-bacterials.They are drugs used to treatinfections caused by bacteria. The first antibiotic was penicillin.
How do antibiotics work?Although there are a number ofdifferent types of antibiotic they allwork in one of two ways:A bactericidal antibiotic kills thebacteria. Penicillin is a bactericidal. Abactericidal usually either interferes withthe formation of the bacteriums cellwall or its cell contents.A bacteriostatic stops bacteria frommultiplying.
If antibiotics are overused orused incorrectly there is achance that the bacteria willbecome resistant - the antibioticbecomes less effective againstthat type of bacterium.http://www.youtube.com/watch?feature=player_detailpage&v=Non4MkYQpYA