Types of Immunity | Human Health & Disease Part 1 | Biology Class 12 | HINDI
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Types of Immunity | Human Health & Disease Part 1 | Biology Class 12 | HINDI

Topic of this presentation is Types of Immunity First of all we will discuss some important terms Ability of our body to fight against disease causing pathogens is called immunity And Body system which is engaged in providing immunity to the organism is called immune system This system develops immunity and fights against pathogens we broadly divide immunity into two categories innate immunity and acquired immunity Innate means from birth The immunity which present in our body from birth is called innate immunity The immunity which acquired after birth on exposure to different pathogens accordingly our body develops immunity against those pathogens that immunity is called acquired immunity acquired immunity is further divided into two categories active and passive which we will discuss in detail ahead We see three lines of defense in immune system we can compare this system with that of Army’s Army has Lines of defense for example infantry is the first line of defense then come lieutenants and then majors and colonels In the same way, we observe lines of defense in immune system there are three lines of defense First line of defense includes physical and physiological barriers Second line of defense includes cellular and cytokine barriers And third line line of defense is the acquired immunity itself we will discus all these lines of defense in detail Skin and Mucous membranes form physical barrier. Mucous membranes line internal body organs These membrane secretes highly viscous mucus that traps many microbes and other foreign substances. And prevent infections of internal organs Mucous membrane of trachea is Ciliated And it propels out trapped dust particles and microbes. Here I want to inform you that cigarette smoke has some chemicals which hamper movement of cilia due to which cilia will not be able to propel properly and won’t be able to propel trapped dust particle and microbes out of the trachea Now these dust particle and microbes will move toward lungs And will cause numerous types of lungs diseases and problems That’s why cigarette smoke is associated with lungs diseases All those components of our body physiology which also provide us immunity kill pathogens, hamper their growth they all constitute Physiological barrier First example is of Hydrochloric acid of stomach and we know that it plays very important role in protein digestion it activates pepsinogen But at the same time it kills microbes and harmful germs present in food. In the same way, an enzyme is present in our body secretions anti-bacterial enzyme which is called lysozyme It attacks bacteria and dissolves their cell wall. Bacteria cannot survive without cell wall In the same way, our gut accommodates some good bacteria which synthesize vitamins they also out-compete bad bacteria and keep their number low in gut And prevent our gut from numerous kind of infections All these components are good examples of Physiological barrier There are two components of second line of defense – cellular barrier and cytokine barrier Phagocytic cells and perforin releasing cells constitute cellular barrier macrophages and neutrophils are phagocytic cells while natural killer cells (NK cells) are perforin releasing cells Phagocytes engulf bacteria or any other kind of pathogen and destroy them we will discuss functioning of NK cells ahead we have shown phagocytic activity of macrophage in this diagram It engulfs bacteria with the help of pseudopodia and food vacuole is formed lysosomes fuses with this food vacuole to form digestive vacuole Bacteria will be digested in this vacuole And the waste product is thrown out of the cell through exocytosis This diagram is showing Diapedesis of WBCs this is the lumen of blood capillary in which blood cells flow as soon as neutrophils know the presence of bacteria at some tissue site then it squeezes out into the interstitial space through endothelial cells and they reach the site of infection and engulf bacteria to destroy them so diapedesis means neutrophils or WBCs squeeze out into the interstitial space through endothelial cells we will discuss Action of Natural Killer cells with the help of this diagram Natural killer cells attack altered self-cells altered self-cells means those body cells which are either virus infected or have become cancerous whenever any of our body cell is altered then it display some specific molecules on its cell membrane which are recognized by NK cells and T cytotoxic cells and they come to know that these body cells have been altered NK cells approach such altered cells and they will start secreting a protein named ‘perforin’ these are the monomers of perforin which will polymerize through cell membrane to form a tunnel like structure and uncontrolled endosmosis will occur through this tunnel like structure and that altered cell will swell and burst and destroy in this way NK cells destroy virus infected cells and cancerous cells when a body cell becomes infected with virus, then it starts secreting a particular kind of chemicals called interferons these interferons diffuse through interstitial fluid to reach neighboring cells and attach themselves with membrane receptors of these neighboring cells to alarm these cells they provide a kind of signal that virus is present in the vicinity now these neighboring cell will synthesize anti-viral proteins this protein helps cells to prevent viral infection here I want to tell one thing that many students have confusion that interferons kill virus interferons never kill virus but prevent them from taking over cellular machinery. we know that virus does not any mechanism of its own these virus use machinery of host cell to synthesize their own proteins and reproduce because interferons prevent viral infections and their spread therefore we use interferons in treatment of many viral diseases for example influenza and hepatitis now we will discuss features of Acquired Immunity first feature is specificity specificity means that if immune system develops immunity against a pathogen then it will become active on encounter of that particular pathogen It means that vaccination against chicken pox will provide immunity against chicken pox only and not against cholera or some other disease It is called specificity Next feature is diversity It is the ability to recognize vast variety of foreign molecules or antigens. and is able to act against those foreign molecules Next feature is discrimination between self and non-self ‘self’ means our own body cells acquired immunity recognizes our body cells and it takes actions against non-self cells only like pathogens, microbes and even grafted tissue acquired immunity treats grafted tissue as non-self due to which a lot many precautions have to be taken during organ transplantation so that acquired immunity does not reject the grafted tissue Next feature is memory It means that acquired immunity retains the memory of encounter of the pathogen and the same pathogen whenever enters the body then acquired immunity becomes active immediately and will raise action against that pathogen and will prevent its infection B- lymphocytes and T- lymphocytes are the main cells of acquired immunity T cells are of two types – T helper and t cytotoxic T cytotoxic cells phagocytose altered self-cells (infected with intra-cellular pathogen or cancerous cells) and are also responsible for graft rejection in organ transplant. whenever organ transplantation occurs in a human All these concepts are discussed in detail ahead we will now discuss difference between B cell and t cells with the help of this table Both kind of these cells are formed in red bone marrow Here I want to eliminate one confusion that many students do have this confusion that RBCs are formed in red bone marrow And WBCs are formed in yellow bone marrow this is entirely wrong concept All types of blood cells are formed in red bone marrow only whereas yellow marrow is a kind of adipose tissue coming back to differentiation both types of cells are formed in red bone marrow B cells are differentiated in red bone marrow itself whereas T cells migrate to thymus gland where their differentiation takes place due to which these cells are called T cells B cells are responsible for Humoral/Antibody Mediated immunity whereas T cells are responsible for Cell Mediated immunity we will discuss both of these type of immunity in detail ahead B cells act against extracellular antigens and pathogens by producing antibodies these antigens and pathogens exists out side the body cells whereas T cells destroy intracellular antigens and pathogens through phgocytosis B cells play their role in tissue rejection through antibody production whereas T cells play direct role in tiisue rejection T cells destroy grafted tissue directly through phagocytosis if no precaution is taken B cells produce Antibodies whereas T cells produce lymphokines and perforins Acquired immune responses are of two types Humoral immune response or antibody mediated immunity and Cell-mediated immune response B cells provide humoral immunity whenever they encounter an antigen, they undergo differentiation with the hepl of T helper cells and they undergo proliferation proliferation means increasing number of cells through cell division these B cells form two types of cells as a result of proliferation – plasma cells and memory cells Plasma cells are active cells and immediately start producing specific antibodies for a particular antigen these antibodies immediately neutralize the antigens and provide immunity to the organism whereas memory cells enter G0 phase and these are long lived suspended cells whenever this particular pathogen or antigen enters the body again then these memory cells will become active immediately and will start producing antibodies against that pathogen we will discuss Humoral Immune Response with the help of this diagram This is a B cell which has encountered an antigen now this is differentiating with the help of T-helper cell and forming two types of cell through proliferation – plasma cells and memory cells plasma cells have started secreting antibodies and these antibodies have started neutralizing antigens or pathogens T-lymphocytes are responsible for Cell-mediated immune response This immunity is raised against altered self-cells. It is responsible for graft rejection in organ transplant because of its ability to differentiate between ‘self’ and ‘non-self’ cells. here I want to tell in brief about tissue matching as blood group is matched before blood donation in the same way Tissue matching is done before undertaking organ transplantation to avoid organ rejection we will now discuss Cell-mediated Immune Response with the help of this diagram this is a virus infected cell and it has displayed viral antigen on its membrane with the help of which Tc cells will recognize these altered body cells and secrete toxic granules which will destroy this altered cell and will prevent replication of virus we will now discuss differentiation between Humoral immune response and Cell-mediated immune response B cells and T helper (TH) cells participate in Humoral immune response T cytotoxic (Tc) cells participate in cell mediated immune response Plasma cells produce antibodies against extracellular antigens and pathogens in humoral response whereas in cell mediated immune response Tc cells produce perforins against intracellular antigens and pathogens B cells play indirect role in humoral response in tissue rejection by producing antibodies whereas in Cell-mediated immune response, Tc cells play direct role by destroying transplanted organ cells B cells do not provide immunity against cancer cells whereas Tc cells kill cancerous cells We will now understand difference between Primary and Secondary Immune Response with the help of this diagram The first encounter with antigen generates primary response. The response is characterized by a long lag phase during which B cells interact with antigens and differentiate into plasma cells and memory cells, followed by increasing antibody level in blood. Primary Immune Response is weaker in strength and antibody concentration in serum is low But when the same antigen is encountered again now the immune system will elicit Secondary Immune Response which is very quick with a short lag phase as there is stored memory of this pathogen in the system memory cells start proliferating immediately as a result, this response is quick and strong there is high concentration of antibodies in serum Secondary Immune Response is initiated in the body due to memory of that pathogen due to this reason Secondary Immune Response is also called anamnestic response we will now differentiate between Primary and Secondary Immune Response with the help of this table The first encounter with antigen generates primary response. lag phase is of longer duration this response is weak Initially IgM, followed by IgG Serum antibody level is low Affinity of antibodies for antigen is also low subsequent encounter with antigen generates secondary response lag phase is of of very short duration response is Very strong Mainly IgG is produced Serum antibody level is high Affinity of antibodies for antigen is also high we will now discuss difference between Innate and acquired Immunity innate immunity is Present from birth It has 4 barriers: Physical, physiological, cellular and cytokines which Form first and second lines of defense this immunity is active throughout the life But it does not have any specificity it does not act against specific pathogen it does not retain memory for any pathogen acquired immunity develops after birth B cells and T cells are its components which form third line of defense the memory cells formed might be short lived or lifelong acquired immunity is specific and also retains memory of the particular pathogen


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