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
