The document discusses the immune system's role in protecting organisms from pathogens, which are agents that can cause disease. It distinguishes between the innate immune system, which provides immediate but non-specific responses, and the acquired immune system, which adapts and improves its response to specific pathogens over time. Additionally, it covers immunity types, the process of vaccinations, and the impact of antibiotics and antibiotic resistance.

1. UNIT 2: THE
IMUNNE
SYSTEMS

2. INTRODUCTION
TO IMMUNITY
• Immune system - system of
•biological structures + processes within
organism:
• protects against disease.
• detect wide variety of agents (pathogens
- viruses, parasitic worms)
• distinguish them from own healthy
tissue.

3. COUNTER ACTION OF
THESE AGENTS
Agents referred to as
pathogens
organism / substance that
could cause a disease.
rapidly evolve + adapt to
avoid detection +
destruction by immune
system.
Multiple defence
mechanisms evolved to
recognize & neutralize
pathogens.

4. PHYSICAL
BARRIER
• Physical barriers prevent pathogens (bacteria +
viruses) from entering organism.
• If a pathogen enters through barriers  innate
immune system provides immediate but non-
specific response.
• Innate immune systems found in all plants +
animals

5. INNATE IMMUNE SYSTEMS
• Cells + proteins  always
present & ready to mobilize
 fight microbes at site of
infection.
• Main components of innate
immune system:
1) physical epithelial
barriers,
2) phagocytic leukocytes
(WBC)
3) dendritic cells,
4) a special type of
lymphocyte (type of
WBC) called a natural
killer (NK) cell,
5) circulating plasma
proteins.

6. ACQUIRED IMMUNE
• If pathogens successfully avoid innate response
vertebrates possess
 2nd layer of protection:
• acquired immune system  activated by
innate response
• Now immune system adapts its response
during infection  improve its recognition
of pathogen.
• Improved response  retained after
pathogen eliminated
• immunological memory
• allows acquired immune system to act faster &
stronger attacks each time this pathogen is
encountered.

7. Differences in the
components of the
immune system
Innate immune system Acquired immune system
Response is non-specific Pathogen & antigen specific response
Exposure leads to immediate maximal
response
Lag time between exposure & maximal
response
Cell-mediated & humoral components Cell-mediated & humoral components
No immunological memory Exposure leads to immunological memory
Found in nearly all forms of life Found only in jawed vertebrates

8. 2. INNATE IMMUNITY
• Innate immune
responses 
• active
immediately upon
infection
• are the same
whether or not
pathogen has
been encountered
previously.
• Includes:
1. barrier
defences &
2. internal
defences

9. 1. BARRIER DEFENSE
SYSTEM
• Includes:
•Skin
•Mucus
membranes of
digestive-,
respiratory-
urinary &
reproductive
tract
oBody secretions:
mucus, saliva
(lysozymes),
tears, oil
secretions, acid
in stomach,
sweat.

10. Mucus membranes •Some cells in
mucus
membrane
produce
mucus.
•Mucus –
trapping
microbes &
other
foreign
particles

11. Trachea  ciliated epithelial cells sweep mucus + trapped
microbes upwards  helping to prevent infection of lungs.

12. • Body secretions create
environment 
unfavourable for microbes.
• Lysozymes in saliva,
mucous secretions + tears
 destroy bacteria as they
enter respiratory tract or
openings around eyes.
• Acid in stomach kill bacteria
• Oils & sweat give human
skin (pH between 3-5) 
acidic enough to prevent
growth of microorganisms.

13. 2. INTERNAL
DEFENSE
If barrier defences
damaged & pathogens
enter body of organism

• 2nd line of defence activated:
Internal defence system
 more sensitive +
includes phagocytosis +
inflammation.

14. PHAGOCYTOSIS Process by
which
phagocytes
ingest / engulf
other cells /
particles.
Phagocyte 
body cells 
leukocyte
(white blood
cell).

15. Different types of
:
• Neutrophils 
engulf & destroy
microbes
• Macrophages
part of the
lymphatic system &
are found
throughout the body
• Eosinophils 
discharge
destructive enzymes
• Dendritic cells 
stimulate
development of
acquired immunity
NEUTROPHIL MACROPHAGE
EOSINOPHIL DENDRITIC CELL

16. PHAGOCYTE
ENGULFING
A
BACTGERIU
M CELL

17. INFLAMMATORY
RESPONSES
• Injured / infected
by pathogens 
signalling
molecules are
released,
• histamine –
stored in mast
cells.
• These molecules
trigger blood
vessels to dilate
& become more
permeable

18. • This increases local blood supply + allow more
phagocytes & antimicrobial proteins to enter tissues
Pus  a fluid rich in WBC, dead microbes, + cell
debris  accumulates at site of inflammation
Fever systemic inflammatory response triggered
by pyrogens (released by macrophages) + toxins
(from pathogens)

19. MAJOR EVENTS IN A
LOCAL INFLAMMATORY
RESPONSE
•Activated
macrophages &
mast cells at injury
site release
signaling
molecules that act
on nearby
capillaries.

20. • The capillaries dilate & become more permeable,
• allowing fluid containing antimibrobial peptides
to enter the tissue.
• Signaling molecules released by immune cells
attract additional phagocytic cells.

21. •Phagocytic cells digest
pathogens & cell debris
at the site, & the tissue
heals

22. ACQUIRED
IMMUNITY
• Acquired immunity  specific immune response system
 specifically detects & destroys pathogens.
• protects us against infectious diseases body learnt
to recognize foreign substances.
• Produces specific reaction to each infectious agent,
REMOVING that PATHOGEN from the body.

23. • Ability to recognize
pathogen that
previously PRODUCED
an immune response is
basis for acquiring
immunity to specific
diseases.
• Thus  we suffer
from many diseases
(chicken pox,
measles etc.) only
once.
• Acquired immunity
involves 2 main
activities:
• Destruction of the
invaders
• Memory of this
response

24. WHICH CELLS ARE
INVOLVED IN ACQUIRED
IMMUNITY RESPONSE?
• Special leucocytes
(WBC), called
lymphocytes
released from
bone marrow.
Some reach the
Thymus gland &
mature  T-
lymphocytes (T-
cells)
Some become B-
lymphocytes (B-
cells) & is present
in bone marrow &
lymph nodes)

25. • Antigens  foreign
molecules on surface of
pathogens (each
pathogen has specific
antigen).
• The immune system has
great amounts of B-
Lymphocytes.
• Each B-lymphocyte is
able to recognize a
specific antigen.
• The B-lymphocytes then
produce antibodies that
will bond to antigens.
• This will neutralize /
destroy pathogen.

26. HOW B-LYMPHOCYTES WORK
antibody
B-lymphocytes
oThe B-lymphocyte form antibodies
o One type of B-lymphocyte is activated by a specific
antigen on the surface of a foreign body

27. The antibodies bond to the antigens & destroy
the foreign body.

28. ACTIVE ACQUIRED
IMMUNITY • Active immunity  a
person has already
been exposed to
antigens (from
pathogens)
• & develops a secondary
response against
specific pathogens.
• Vaccinations  develop
primary response, then
if they are exposed to
pathogens later 
active immunity helps
to fight them off.

29. PASSIVE IMMUNITY
• In natural passive
immunity, antibodies 
passed from mother to
child.
• Antibodies can be
transferred through the
placenta, or transmitted
through the colostrum.
• Colostrum 
milky yellowish fluid
produced by the milk glands
of mammals  first few
days after giving birth,
before true milk appears.
• It contains proteins,
carbohydrates, fats,
vitamins, minerals, &
proteins (antibodies)
that fight disease-
causing agents such as
bacteria & viruses.

30. • Antibodies transmitted
through colostrum /
placenta only last for
several weeks
• long enough to
allow baby to start
to build up its own
immune system &
make its own
antibodies.
• Artificial passive
immunity involves the
introduction of
antibodies through
means such as injection
- VACCINATIONS.

31. HUMORAL
IMMUNITY
& CELL
MEDIATED
IMMUNITY
Humoral Immunity -
infectious agents in the
blood & body tissues
• managed by B-cells (with help from
T-cells).
Cell Mediated - Cell-
mediated immunity - deals
with body cells that have
been infected.
• The cell-mediated system is
managed by T-cells.

32. VACCINATIONS
• All vaccinations
work by
presenting a
foreign antigen to
the immune
system in order to
evoke an immune
response, but
there are several
ways to do this.
• We will look at 4
methods:

33. 1. Using an
inactivated
vaccine
• Inactivated vaccine  virus / bacteria grown in culture 
killed .
• Virus / bacteria particles  destroyed & cannot replicate,
BUT:
• virus capsid proteins or bacterial wall are intact enough
to be recognized & remembered by the immune system.
• This evokes an immune response.

34. 2. Using an
attenuated vaccine
• Attenuated vaccine,
live virus or bacteria
 very low virulence
are administered.
• They will replicate
locally or very slowly.
• Which causes an
immune response to
produce antibodies.

35. 3. Virus-like particle
vaccines
• Virus-like particle vaccines
consist of viral protein(s)
derived from structural
proteins of a virus.
• These proteins self-assemble
into particles that resemble
the virus (from which they
were derived) but lack viral
nucleic acid,  not
infectious.
• Human papillomavirus &
Hepatitis B virus.

36. 4. A subunit vaccine
• A subunit vaccine
presents an antigen
to the immune
system without
introducing viral
particles.
• One method:
isolation of specific
protein from virus /
bacterium 
administering this by
itself.

37. ANTIBIOTICS •Antibiotics are
also known as
anti-bacterials.
•They are drugs
used to treat
infections
caused by
bacteria.
• The first
antibiotic was
penicillin.

38. ANTIBIOTICS
• In 1952, penicillin was fully
effective against all strains of
staphylococcus bacteria, to such
an extent that by the early 1960s
the U.S. surgeon general, William
Stewart, felt confident enough
to declare: “The time has come to
close the book on infectious
diseases. We have basically
wiped out infection in the United
States.” Even as he spoke,
however, some 90 % of those
strains were in the process of
developing immunity to
penicillin. Soon one of these new
strains, called Methicillin-
Resistant Staphylococcus Aureus,
began to show up in hospitals.
Only 1 type of antibiotic,
vancomycin, remained effective
against it, but in 1997 a hospital
in Tokyo reported the
appearance of a strain that could
resist even that. Within months it
had spread to six other Japanese
hospitals. All over, the microbes
are beginning to win the war
again.

39. ANTIBIOTICS
• As James Surowiecki has
noted, given a choice
between developing
antibiotics that people
will take every day for
two weeks or
antidepressants that
people will take every
day forever, drug
companies not
surprisingly opt for the
latter.
• Although a few
antibiotics have been
toughened up a bit, the
pharmaceutical industry
hasn’t given us an
entirely new antibiotic
since the 1970s.

40. How do antibiotics work?
• Different types of
antibiotic,
• they all work in one
of two ways:
• Bactericidal
antibiotic  kills the
bacteria.
• Penicillin is a
bactericidal.
• Bactericidal 
interferes with
formation of
bacterium's cell
wall or cell
contents.
• Bacteriostatic stops
bacteria from
multiplying.

41. Antibiotic Resistance
• If antibiotics are overused or used
incorrectly
• chance that the bacteria will become
resistant –
• the antibiotic becomes less effective
against that type of bacterium.