its all about immunity and defense mechanisms

1. BS MICROBIOLOGY
NumanaAslam

2. immunity and its
types

3. immunity
 Immunity is a resistance and protection of biological systems by means of
cells and molecules against non self molecules and invading microbes
without any pathological change.
 Molecules that are to be detected by cells of body are of two types :
 Self molecules and non-self molecules.
 Self molecules:
 chemical composition is known.
 immune system doesn’t show any response against self
molecules.
 Non-self molecules:
 chemical composition is unknown.
 when a non-self molecule tries to enter in body or get
entry in the body ,it is detected by the cells of the body and produce
immune response against those molecules.

4. Auto immune system
 Auto immune system Is defined as the system in
which immune system start breaking the body
cells by its own.we can say that there is no need
of response but immune system intentionally
start producing response against the healthy
body cells and tissues and harm them .this type
of system is reffered as auto immune system

5. Response of Immune system
 Immune system repond against the non-self molecules .
 Non-self molecules are any foreign particulate particles also called as
antigen
 So we can say that immune system’s response against antigen Is also called
as immunity.
 Response is aquired through either cells or molecules of the body.
 Response acquired through molecules is reffered as humoral.
 Response acquired through cells is termed as cellular.

6. Types of immunity
Innate(natural) immunity Addaptive(aquired) immunity
 Innate immunity is present by birth.
 It is non-specific.(because it
produces response against the
chemicals and invading particles in
the same way)
 It always produce a quick response.
 Memory cells are not present.
 Number of encounters are not
stored.
 Level ,extent,reaction not change
while in addaptive it changes.
 Addaptive immunity develops with
the passage of time upon exposure to
microbes.
 It is specific.(whenever a non-self
molecules enter in a body immune
system produces a response
differently)
 In addaptive type response is
somewhat different ,on first exposure
to microbes it takes time but on the
second entry of microbe response is
quick .
 Memory cells are present that
remember the entry of microbes .
 Number of encounters are stored.

7. Immunity can be aquired by two
means
 Natural as well as addaptive immunity is aquired through :
 Active mechanism
 Passive mechanism
 Active mechanism:
 in which body system itself show response.
 Example:
 hepatitis virus is defended by active mechanism.

8. Passive mechanism:
 Where immune system doesn’t perform any function.In this system
individual is given antibodies produced by some one else.
 Adaptive immunity Is further classified as:
 Natural and artificial
 Natural and artificial further classified as:
 Active and passive immunity.
 Naturally acquired active immunity (infection).
 Naturally acquired passive immunity (maternal).
 Artificially acquired active immunity (immunization).
 artificially acquired passive immunity (antibody transfer).

9. Recongnition of self and non-self molecules:
 Immunity discriminate the self and non self molecules through receptors
called as toll like receptors (TLR) present in plasma membrane in form of
clusters,and protein in nature. Toll-like receptors activate phagocytes and
tissue dendritic cells to respond to pathogens.
 For instance:
 Gram negative bacteria: have lipopolysaccharides in the walls of cells as
well as outside the cell walls in hangingsuspended form.
 Gram positive bacteria: have techoic acid in cellwalls and is non-self
molecule ,which will be recongnized by the receptors
 there are different types of receptors for different molecules or
foreign particles;
Examples:

10.  Motile bacteria have flagella for movement consist of flagellin protein
which is a non-self molecule and incompatibe to human body.
 Fimbrae one of external structures of cell walll of bacteria containing
fimbrin protein also incompatible to human body and recongnized as a
non-self molecule by receptors present in cell.
 Information (size,molecular weight,composition,and configuration)
about foreign particle pass to the cells through the receptors.

11. When toll like receptors recongnize a microbe or non-self molecule it sends
a message to nucleus to produce response against these molecules.
That in return transmit information to the immunity cells .
TLR (pass information to the nucleus to produce cytokines
chemicals (cytokines)
trnasmit signals to the immunity cells

12. Innate immunity
 Innate immunity is non-specific.
 There are no memory cells in innate immunity that will recongnize the microbes
on their second entry.
 Innate immunity produces a rapid response against microbes or non-self
molecules.
 Number of body cells or immunity cells do not increase on the exposure of cells
to non-self molecules or microbes.
First line of defense:
immunity defends on the basis of three components.
 Physical barrier
 Chemical barrier
 Microbiota(microflora)

13. Phycical barriers
Physical barriers are of different types that help in preventing body from
microbes.
 Skin
 Mucous membrane
 Respiratory system
 Conjuctiva
 Ear
 Oral cavity
 Digestive system
 Skin:
skin is the largest organ of the body in aspects of surface area and play
a role in prevention of body against microbes.

14. Skin consist of two layers:
 Epidermis(in epidermis epithelial cells are closely packed,microbes cannot
pass through the epidermis due to close packing of cells,cells of outer
surface or epidermis are almost dead)
 Dermis(in dermis cells are not closely packed ,there are spaces among cells
so mocrobes may pass through if they get entry in the body through
epidermis).
Desqoumation:
desqoumation is the process of removal of dead cells of the
body(outer layer of epidermis) and also in removal of microbes.
 Desqoumation accurs naturally.

15.  Keratin:
keratin is a protein present in membranes of the cells and also ceases
the passage of microbes through the skin.
 If microbes want to get entry in the skin they have to hydrolyze the keratin
that accur only in the presence of enzymes.
 80% cells of the skin are dry that act as a barrier against microbes.
 15-20% cells are moist where microflora is present for the protection
and it is present naturally.
For instance:
athelets foot is a disease caused by a fungus when moisture is
present on the skin.

16. Mucous membrane:
Mucous membrane another barrier for microbes.
If we compare mucous membrane with skin there are following differences:
 Mucous is present in between cells and tissues while not present in skin.
 In case of mucous membrane outermost cells are not dead cells while in skin
dead cells are present.
 Mucous membrane is wet due to presence of mucous in it while skin is dry.
 Keratin is not present in mucous membrane while present in skin.
 Resistance against microbes is less in mucous membrane than skin.
 Hinders microbes physically.
for instance:
nostrils,trachea,nasal,lungs,urinogenital system have mucous in
membranes.

17. Respiratory system:
 Moist hair are present in nostrils and particles get attached to them
 Cilia as a physical barrier present on the epithelial cells of the respiratory
system,due to cilliary motion microbes do not get attached to upper
respiratory system.but of the cilia are destroyed or damaged microbes get
entry in the upper respiratory system.
 Cilia are damaged due to dusty environment or chemicals etc.
For instance:
in case of smokers there are more chances of entry of microbes
because of destruction of cilia due to carcinogen present in the cigerrete smoke.
Microbes trap in mucous and with damaged cilia move to the upper respiratory
system and cause disease called respiratory disease . For example bronchitis.

18.  Epiglottis:
a flap of cartilage behind the root of the tongue, which is
depressed during swallowing to cover the opening of the windpipe.
Two functions are performed by the epiglottis:
 During eating respiratory system is protected.
 During inhalation digestive system is protected.
Epiglottis also prevent the entry of microbe but if it is damaged it may allow the
microbe to enter.
 Epiglottis genitically infected:
epiglottis get infected due to excess of
exercise because more oxygen and energy is required during this process and
when we take up food and water immediately it effects epiglottis and microbes
get entry in the respiratory tract along food particles.

19.  Inflammation:
a localized physical condition in which part of the body
becomes reddened, swollen, hot, and often painful, especially as a
reaction to injury or infection.
if inflamation of voice box accur it will exert pressure on the epiglottis and
its barrier may break and hence microbes will get entry.
 sneezing:
it’s a physical barrier
 It is a mechanism of innate immunity may exhale the microbes from
the body.
How?
it works due to contraction of muscles ,first we take a small
amount of air inside before the process of sneezing because muscles
require energy to perform the action.

20.  Coughing:
through the process of coughing mucous (cellular debris) is
expelled from the body.
 When cell death accurr due to apoptosis microbes are present in the cellular
debris and by the process of coughing it is expelled and also reffered as
sputum.
Conjuctiva:
it is also a physical barrier that help in prevention against
microbes

21.  Lacrimal glands present in he upper lids of the eye produce tears when
exposed to the microbes and remove the microbes but when these lacrimal
glands are damaged microbes get entry and cause disease.
 Ear:
ear also contain mucous membranes .
 Usually H2O2 is used to remove mucous from the ear that in return injured
the membranes and chances of trapping of microbes increased.
 Oil is als used but due to oil membranes become more oily and microbes
trap easily.

22. Oral cavity:
 In oral cavit slivary glands are present.
 The process of salivation is innate meachanism of immunity.
 The process of salivation is used in washing of micro organism.
 When oral cavity is damaged due to toothpick,miswak,coa,salt and soda ,it
allow microbes to enter and cause disease.
 Fibrous food may cause injury .
 Digestive system:
Digestive system is also a defense system against microbes.following processes
are involved that help to expel the microbes from the body.
 Vommiting:

23.  Vommiting involves in physical barrier of innate immunity.
 It is involuntary action.
 And accurr in response to toxins,vommiting accurr due to deficiency of O2 is
reffered as hypoxia.
 When vommiting stops ,microbes get absorb in the stomach again.
Diarrhoea:
a condition in which faeces are discharged from the bowels
frequently and in a liquid form.
 It is also a mechanism of innate immunity.
 When diarrhoea get absorb ,it may cause death.

24.  Urination:
urination is a washing of genital system and also help in removal of
microbes from the body.

25. Chemical barriers:
 Glands are organ in the human or animal body which secretes
particular chemical substances for use in the body or for discharge into
the surroundings.
 They strengthen physical barriers .
 Lacrimal glands:
lacrimal glands are secretary cells and protect conjuctival
glands.
 They provide protection in form of tears. For instance: lysozyme is an
enzyme present in the tears that target peptidoglycan in the walls of
gram positive bacteria and to some extent gram negative bacteria and
cause death of bacteria .

26.  Slivary glands:
slivary glands are present around digestive system that produce
sliva to dilute the number of microbes and it contain highest concentration of
microbes that will be expelled from the body after production.
 Mucous:
mucous contain lysozyme (hydrolyse the peptidoglycan which is the
major component of gram positive bacteria and cause lysis of the cell).
 Mucous collect the microbes in the form of plug and then remove it from the
body.

27.  Gastric juice:
gastric juice, thin, strongly acidic (pH varying from 1 to
3), almost colorless liquid secreted by the glands in the lining of the
stomach. Its essential constituents are the digestive enzymes pepsin and
rennin , hydrochloric acid, and mucus
 When ph is less than 4 ,death of microbes accurr.
 Enzymes present in stomach cause digestion of microbes.
 For instance :
Halicobacter pylori this bacteria reach stomach due to small
wounds but HCl present in stomach doesn’t act on it and cause disease
called ulcer .

28.  Clostridium botulinum and Staphlococcus aureus cause spoilage of foodand
produce toxins and there degradation doesn’t accurr and hence cause
disease.if vommiting and diarrhoea do not respond then both bacteria will reach
there target site and ultimately cause death.
 Urinary system:
The urinary system, also known as the renal system,
consists of the kidneys, ureters, bladder, and the urethra and glands are
present in this system that produce secretions in the form of urine having
akaline pH where no bacteria can grow so ,it helps in removal or death of
microbes from the body but if pH is diturbed using chemicals from plants and
animals, it may allow the microbes to attack. For instance: urine naturally
defends against vaginal thrush caused by a fungus called Candida
albicans.

29.  Skin:
in skin secretary cells are sebaceous glands that produce
sebum(contain unsaturated fatty acids due to which skin hair remain oily and
prevent from microbes )but if skin hair are dry they may become brittle and in
result breakage of brittle hair accur and the site for the entry of microbes will be
free
Excess and absence of sebum cause acne .
 Fatty acids provide protection of hair and make the pH acidic so that
microbes do not grow and there will be no chance of disease and sebum
contain lysozyme enzyme that cause lysis of the bacterial cell.
 If sebum and fatty acids are not emulsified ,microbes present on skin
convert unsaturated fatty acids to saturated fatty acids having smell and
result will be smelly sweat.

30.  Perspiration:
perspiration is the process of sweating.this is the secretion
of skin cells containing lysozyme . they secrete the salts which maintain the
osmosis and high salt concentration kill microbes but some microbes can grow
in halophilic environment for example : Staphlococcus aureus
 If these are not removed or washed out they may cause formulation of
pimples and then converted into pustules.

31. Microbes(microbiota or
microflora):
 This a type in which useful microbes present on skin defend the body
against the environmental microbes
 Microbes reside on the skin and mucous membrane following relationship
called commensalism(both individual are beneficial for eachother) .
In case of microflora following factors are involved:
 Space
 Nutrition
 pH
 Solubility
 Space :
microbes present on skin provide protection against lethal microbes
present in environment but products like bleech destroy microflora and the
chances of enterance of microbes will increase.

32.  Nutrition:
if microbes succeeded to find the space on the skin to enter but
they will be failed to find nutrition because microbes present on skin wouldn’t
allow them to take nutrition due to competitive exclusion and once again
person will be detected from the entry of the microbes.
 pH:
desqoumated cells are taken up by the microbes as a source of nutrition
and the pH of skin become acidic and microbes cannot grow in acidic pH and in
result individual is protected from the entry of microbes.

33.  Solubility:
Escherichia coli live in intestine and produce bacteriocins
(soluble protiens )in the result of metabolism and these proteins help in killing
microbes like Shigella and Salmonella that cause intestinal diseases .
Take up of antibiotics disturbs the E.coli and in result environmental microbes
cause diseases .

34. 2nd line of defence:
 Reticuloendothelial cells (lymphoid cells) act as a second line of defense.
lymphoid cells in mammals are of two types:
 Primary
 Secondary
 Primary:
primary lymphoid cells are present in bonemarrow and spleen.
 Secondary:
secondary lypmhoid cells are present in thymus,tonsils,payers
patches(in the walll of intestine lynphoid cells are present in the form of
clusters),liver and kidney.

35.  In birds in place of bonemarrow bursa of fabricious is present.
 When microbes enter the body after breaking the first line of defense ,the
lymphoid cells fight against them(second line of defense).
For instance:
 Neutrophils engulf bacteria and kill them by the process called
phagocytosis.
 Macrophages are phagocytic against microbes and infection.it is mainly for
viruses and fungi etc.
 Eosinophils these are mainly for protozoa.its first role is in tissues called
mast cells
 Dendritic cells engulf those microbes that enter through the skin by the
process of phagocytosis.

36.  lymphocytes are reffered as naturally killer,engulf those bacteria enter
through blood. Lymphocytes are of two types B-lymphocytes and T-
lymphocytes.
 Cytotoxic T-cells are T-lymphocytes that kill cancer cells,cells that are
infected particularly with viruses .
macrophages
Wandering fixed
Wandering macrophages which are located in certain organs
roam the wandering tissues and tissues,fixed macrophages
and gather at infections site. Are found in liver(kuffer’s cells).

37. wandering cells circulate in fixed macrophages present in diff
Blood(monocytes) and then organs and tissues but do not
migrate to the other tissues circulate.
and become macrophages those present in tissues called
histiocytes.
those present in liver called Kupffer’s
cells.
those present in lungs called alveoler
those present in brain called
microglial.

38. Phagocytosis:
 Phagocytosis is a first mechanism of 2nd line of defense.
 When an infection accurrs both granulocytes (especially neutrophils)and
monocytes migrate to an infected area and primarily neutrophils are
dominant and fight against the infection but when infection progresses
macrophages will attack .
 Macrophages are either wandering or fixed .
 Mechanism of phagocytosis:
phagocytosis is mainly divided in four phases:
 Chemotaxis
 Adherence
 Ingestion
 digestion

39.  Chemotaxis:
chemotaxis is the chemical attraction of phagocytes to the
microbes.After attachment of phagocytes with microbes they engulf the
microbes.
 Adherence:
Adherence is attachment of phagocyte’s plasma membrane to
the surface of microbes. Attachment of microbes can be enhanced by the
presence of coating of serum proteins on the surface of microbes.
 Process of this coating is called opsonization.
 The proteins that act as opsonins include some components of the
complement system and antibody molecules.

40.  Ingestion:
during this process the plasma membrane of the phagocytes extends
and projection are formed called pseudopodia that engulf microbes,then
microbe surrounded by pseudopods and they meet and fuse to form
phagosome.The membrane of phagosome has enzymes that pump protons
into phagosomes ,reducing pH to 4.At this pH hydrolytic enzymes are activated.
 Digestion:
in this phase of phagocytosis,phagosome pinches off from the
plasma membrane and enters the cytoplasm .in cytoplasm it fuse with
lysosome and form phagolysosome.Its contents take almost 10-30 minutes to
kill almost all types of bacteria.
Lysozyme enzyme present in the lysosome and in addition to this other enzyme
are also present like protease ,nuclease etc..

41.  Lysozyme act on peptidoglycan of cell wall of bacteria.
 Lipase act on lipids and lipids are converted into fattyacids.
 Protease act on proteins and digest them.and convert them into peptides
etc.
 Nuclease act on nucleus and convert it into nucleotides.
 In phagosome only those things will remaain left that cannot be digested
even in presence of enzyme and these things are not useful for phagosomes
and are reffered as residual bodies in the form of pus.And then residual
bodies are discharged from the cell.
Debris of cell : cellular debris
Debris of microbes: microbial debris

42.  Some other enzymes are present in lysosomes that can produce toxic
oxygen products .Toxic oxygen produced by the process called oxidative
burst.
 Certain bacterial capsular composition is known to phagocytic cells means
they cannot recongnize them as the non-self molecules and they get entry
in the body and hence cause disease .
For instance:
Bacillus anthrasis
haptens(a small molecule which, when combined with a larger
carrier such as a protein, can elicit the production of antibodies which
bind) specifically to it

43. Inflamation:
 Inflamation Is the second mechanism of 2nd line of defense.
 Damage due to bodie’s tissues triggers a defensive response called
inflamation.
 The damage can be caused by microbial infection and physical agents.
 Symptoms of inflamation: redness ,pain ,heat,swelling and loss of
function.
inflamation
Two types:
 Acute inflamation
 Chronic inflamation

44.  Acute inflamation:
when the cause of inflamation is removed in short time then
inflamatory response will be intense ,it is reffered as acute inflamation.
For instance: response to a boil caused by Staphlococcus aureus.
 Chronic inflamation:
when the cause of inflamation cannot be removed easily and
it takes a long time ,also the inflamatory response will be less intense and long
lasting,then it is reffered as chronic inflamation.
For instance: response to a chronic infection such as tuberculosis caused by
Mycobacterium tuberculosis.

45.  Functions of inflamation:
There are following fuctions of inflamation:
 To destroy the injurious agents
 If destruction is not possible then limit the microbes and there effect on
body
 To repair and replace tissue damaged by the injurious agents or its by-
products.
During inflamation there is an activation and increased concentration of group
of proteins in blood called acute-phase proteins.Some acute-phase proteins
are produces by liver and some are present in blood in inactive form naturally
and on exposure to infection or microbe these proteins are converted to their
active forms to perform their relative functions .

46.  For instance:
when mast cells are infected or injured ,they produce acute-phase
proteins called histamine.basophils and platelets are also produce histamine.
Vasodilation and increased permeability of blood vessels:
immediately following tissue damage ,blood vessels dilate (increased
diameter ) in the area of damage ,and the permeability of blood vessels
increase.Dilation of blood vessels also reffered as vasodilation,increased blood
flow to the damaged area is responsible for redness(erythema) and heat
associated with inflamation.
 Due to increased permeability the blood moves from the vessels to the
tissues ,and is responsible for edema.

47.  Vasodilation and increased permeability of blood vessels are caused by
chemicals released by damaged cells in response to injury .
for instance:
 histamine present in many cells especially in mast cells in connective
tissues,basophils and platelets etc.
 Kinins are present in already produced form in blood plasma,cause
vasodilation and permeability of blood vessels .
 Prostaglandins play role to intensify the effect of kinins and histamine and
help phagocytes to move through capillary walls.
 Fibrinogen play role in blood clotting, molecules can be trapped in clot and
not allowed to disperse anymore.
 Complement play role same as histamine ,kinins etc .In addition to
these,they also help in chemotaxis ,phagocytosis and increase opsonization.

48.  If these products are produced in limited amount then inflamation will be a
beneficial process but if these products are unlimited then inflamation is not
beneficial.
 Due to increase in permeability spaces are formed between cells when fluid
(neutrophils and monocytes )are reabsorbed and stick to the walls of blood
vessels , this process is reffered as margination.
 Then collected phagocytes begin to squeeze between the endothelial cells
of the blood vessels to reach the damaged area . This migration which
resembles the ameboid movement ,is called emigration (diapedesis).
 After phagocytosis all injured cells ,monocytes,neutrophils and
macrophages are killed and debris(cellular debris) produced and pus formed
on the site of injury .

49.  pus:
pus is localized colection of a mixture of dead cells and body fluids .
 Abscess:
abscess is a cavity enclosed pus.Stimulus of inflamation never stop and
the phagocytes fight against microbes continously,abscess increased and due
to pressure it bursts and microbes are eliminated from the abscess.
 When abscess is ruptured artificially, physical injury accurr again and all
processes are repeated again.