OVERVIEW OF THE IMMUNE SYSTEM AND BODY'S DEFENCE SYSTEM.pdf

Immunology

1. Definition of terms
➢ Immunology
➢The study of the immune system or immunity
➢the study of all aspects of host defense against
infection and of adverse consequences of immune
responses.
➢The study of the physiological mechanisms which
enable the body to recognize materials as foreign and
to neutralize, metabolize or eliminate them without
injury to the host tissue.

2. cont…
Immunity
➢State of protection from infectious diseases
Immune system
➢ A remarkably versatile defense system that has evolved
to protect animals from invading pathogenic
microorganisms and cancer.
➢ It is able to generate an enormous variety of cells and
molecules capable of specifically recognizing and

3. eliminating an apparently limitless variety of foreign
invaders.
cont…
antigen
➢It is any foreign substance that when enters the body
activates the immune response.
antibody
➢ Is a protein produced by the B lymphocytes to attack and
fight off antigens.

4. Fluid Systems of the Body
• There are two main fluid systems: blood and lymph
• They are intertwined throughout the body
• Theyare responsible for transporting the agents of the immune
system.

5. The Blood System
• 5 liters of blood of a 70 kg person constitute about 7% of the body's
total weight
• Composed of 52–62% liquid plasma and 38–48% cells
• Three types of blood cells:
1) Erythrocytes (red blood cells or RBCs),
2) Leukocytes (white blood cells or WBCs),
3) Thrombocytes (platelets)
Three types of blood cells:

7. Leukocytes
• Further subdivided into:
▪ Granulocytes (containing large granules in the cytoplasm)
▪ Agranulocytes (without granules)
Granulocytes consist of:
– Neutrophils (55–70%),
– Eosinophils(1–3%),
– Basophils (0.5–1.0%).
Leukocytes…….

8. • Agranulocytes are:
• Lymphocytes (20-40%) - Consisting of B cells and T cells
• Monocytes (1-6%)
• Lymphocytes circulate in the blood and lymph systems, and make
their home in the lymphoid organs.

11. Erythrocytes
• RBCs are produced each second and each lives for about 120 days
• RBCs antigens used in ABO blood grouping
• Grouping is characterized by the presence or absence of A and/or
B antigens on the surface of the RBCs.
• Blood type AB means both antigens are present
• Type O means both antigens are absent.
• Type A blood has A antigens and type B blood has B antigens.

13. The Lymph System
•There are small bean-shaped lymph
nodes that serve as filters of the
lymphatic fluid.
•It is in the lymph nodes where antigen
is usually presented to the immune
system.
Understanding the
lymphatic system
• The lymphatic system consists of organs, ducts,
and nodes. It transports a watery clear fluid called
lymph

14. • Fluid distributes immune cells and other factors throughout the body. It also
interacts with the blood circulatory system to drain fluid from cells and
tissues.
• The lymphatic system contains immune cells called lymphocytes, which
protect the body against antigens (viruses, bacteria, etc.) that invade the
body
Main functions of the lymphatic system
• The lymphatic system aids the immune system in destroying pathogens and
filtering waste so that the lymph can be safely returned to the circulatory
system.
• To remove excess fluid, waste, debris, dead blood cells, pathogens, cancer cells,
and toxins from these cells and the tissue spaces between them.

15. • The lymphatic system also works with the circulatory system to deliver
nutrients, oxygen, and hormones from the blood to the cells that make up the
tissues of the body.
Blood capillaries allow fluid to leave, and enter, the circulatory system

17. Lymph organs
• Include the bone marrow, lymph nodes, spleen, and thymus. Precursor cells
in the bone marrow produce lymphocytes. B-lymphocytes (B-cells) mature in
the bone marrow. T-lymphocytes (T-cells) mature in the thymus gland.
• the ducts of the lymphatic system provide transportation for proteins, fats,
and other substances in a medium called lymph.
• "Means clear water and it is basically the fluid and protein that has been
squeezed out of the blood (i.e. blood plasma).

18. The immune system

1.3. The immune system
Immune System
In nate
( Nons pecific )
Ada ptive
( Spe cific )
Cellular
Components
Humoral
Components
Cell - Mediated
Humoral
( Ab )

19. Overview of the Immune System

20. The Innate immunity
Natural immune system (Innate Immunity)
✓ Non – specific
✓ First line of defense
✓ Repeated exposure - no augmentation
◼ Components
✓Biochemical
✓Physical barrier
✓Cells
1. Components

21. a. Biochemical
◼ enzymes, C’, etc.
◼ secretions
◼ pH
b. Physical
◼ skin
◼ Mucous membrane
c. Cells
◼ Phagocytes, NK

22. cont…

23. Lysozymes
Mucus
Sebaceous glands
Skin
Cilia: trachea
Acid in
stomach
Commensal
organisms in
gut & vagina
Spermine in semen

24. Innate immunity
◼ It is divided into two parts
 1
st
line of defence (External Innate Defense system)
 2
nd
line of defence (Internal Innate Defense System)

25. 1. External Innate Defense Systems
◼ Skin
 Keratinzed dead layer, sweat and sebum, hair and normal
flora
◼ Mucous membrane
 Mucus and cilia
 Gastric acid
 Vagina ph
 Urine ph
 Saliva and tears

27. cont…
cont…
◼ Prevent entrance:
 Structural barriers – effective with most
microorganisms
◼ Skin - epidermis = layers of tightly packed epithelial
cells. Outer layer is dead cells and
keratin, waterproofing protein
◼ Inner layer skin - dermis = blood vessels, hair follicles,
sweat glands, and sebaceous glands that produce an
oily secretion called sebum
◼ Cilia and cough reflex – helps expel microbe
containing mucous
◼ Sneeze

28. cont…
◼ Mucus - conjunctivae, alimentary, respiratory, and
urogenital tracts
• saliva, tears, and mucous secretions wash away
invaders and contain antibacterial or antiviral
substances.
• acidity (pH 5.6) of sweat, sebaceous glands, vagina
(pH 5) and stomach (pH 1) – unfriendly to many
microorganisms
◼ enzymes present in the skin and stomach, tears
◼ Normal flora - out compete pathogens for attachment
sites on the epithelial cell surface and for necessary
nutrients.

29. cont…
2. Internal Innate Defense System
◼ Cells
 Neutrophils, eosinophil, basophils and mast cells
 Dendritic cells and monocyte (macrophages) antigen
presenting cells
◼ Physiology
 Inflammation
 fever
◼ Chemicals
 Interferon

30. cont…
 Complement proteins and other chemicals produced by
the cells
◼ To prevent expansion of penetration
 Recognize carbohydrates not normally present on cells
such as mannose
 May cause nonspecific activation of white cells
◼ Phagocytosis – by neutrophils, eosinophils, basophils, or
macrophages, mast cells, and dendritic cells
 Clotting mechanism which entraps organisms in fibrin
clots
 Complement System can lyse cells or enhance
phagocytosis

31. cont…
Physiologic Barriers
◼ Soluble factors contribute to innate immunity, they are
collectively known as acute phase reactants.
◼ Normal serum components, non-specific responders to
inflammation
◼ Increase because of infection, injury, trauma
◼ Produced mostly by liver in response to inflammation and
cytokine stimulation
 Cytokines: IL-1, IL-6 and TNF alpha which are produced by
macrophages and monocytes at inflammatory site are activators

32. cont…
◼ Complement – a series of enzymes normally circulating
in an inactive form
 May be activated by the classical or alternate pathways
 Can result in lysis or enhanced phagocytosis of cells
◼ Lysozyme, a hydrolytic enzyme in mucous secretions
and in tears, can cleave the peptidoglycan layer of
bacterial cell wall.
◼ Interferon, proteins produced by virus-infected cells.
Has many functions including ability to bind to nearby
cells and induce a generalized antiviral state.
◼ Phagocytosis
 Is a form of endocytosis.

33. cont…
 Important body defense mechanism is process in which
specialized cells engulf and destroy foreign particles
such as microorganisms or damaged cells.
 Macrophages and segmented Neutrophiils are the most
important phagocytic cells.
◼ Can be divided in to several stages:
 chemotaxis – attraction of leukocytes or other cells by
chemicals
 Movement of neutraphils is influenced by chemotaxins –
chemical messangers

34. cont…
◼ Complement, proteins from coagulation,
◼ Products from bacteria and viruses,
◼ Secretions from mast cells, lymphocytes, macrophages,
and other neutrophils Phagocytosis
◼ Phagocytic cells Chemotaxins such as
 Complement components
 Coagulation cascade proteins
 Bacterial and viral products ◼ Attract phagocytic cells
including:
 Mast cell, lymphocyte, macrophage, neutrophil products
◼ Physical contact between phagocytic cell and foreign
object results in

35. cont…
 Formation of phagosome
 Digestion
 Release of debris
◼ Phagocytosis ...
 Adherence – binding of organism to the surface of
phagocytic cell.
 Engulfment:- is the ingestion and formation of
phagosomes.
 Digestion – after the foreign particle is ingested,
cytoplasm lysosome fuse with phagosome Th e

36. cont…
enzymes of lysosome then contribute to microbial killing
and lysis.
Phagocytosis ...

37. cont…

Source: Kuby immunology 2007, 5
th
ed

38. 1.5. The adaptive immune system

The adaptive immune system
Immune System
In nate
) pecific Nons (
Ada ptive
( Spe cific )
Cellular
Components
Humoral
Components
Cell - Mediated
Humoral
( Ab )

40. The adaptive immune system
Adaptive Immunity
➢ Specific
➢ Second line of defense
➢ Repeated exposure - augmented – memory
➢ Faster response
➢ More vigorous response
➢ Longer lasting response
Components
Classic Immune System
➢ Cells (Cell mediated) =CMI
➢ Soluble Factors (Humoral immunity) = HI
◼ It is divided into two

41.  Humoral
◼ B cell – plasma cells (antibodies) and memory cells
 Cell mediated
◼ T cells
 T helper cells (CD4+) - activated cells and memory cells
 Cytotoxic T cells (CD8+) – activated cells and memory cells
 T regulatory cells
The adaptive immune system
◼ Capable of recognizing and selectively eliminating
specific foreign microorganisms and molecules(i.e.,
foreign antigens).
◼ Unlike innate immune responses, adaptive immune
responses are reactions to specific antigenic challenges

42. ◼ Different populations of lymphocytes and their products
are the major actors together with accessory cells –
Antigen presenting cells (APCs) ◼ Cardinal features
are :
 Specificity
 Diversity , Memory,
The adaptive immune system
Cardinal Features of adaptive Immune Responses
◼ Specificity –
 specific for distinct antigen, and for different structural
components of a single complex protein,
polysaccharide, or other macromolecules.

43.  Portions of such antigens recognized by individual
lymphocytes are called determinants or epitopes.
 This fine specificity exists because individual
lymphocyte express membrane receptors able to
distinguish subtle (slight) differences in structure
between distinct antigens.
The adaptive immune system
◼ Diversity- total number of antigenic specificities of the
lymphocytes in an individual, called the lymphocyte
repertoire, is extremely large.
 estimated mammalian immune system can discriminate
10
9
to 10
11
distinct antigenic date ruminants.

44.  This property of the lymphocyte repertoire is called
diversity. It is the result of variability in the structures
of antigen- binding sites of lymphocyte receptors for
antigens.
The adaptive immune system
◼ Memory- Exposure of the immune system to foreign
antigen:
 enhances its ability to respond again to that antigen.

45.  Responses to second and subsequent exposure to the
same antigen, called secondary immune responses,
are usually more rapid and larger than the first or
primary immune response.
The adaptive immune system
◼ An effective immune response involves three major
groups of cells: Cellular Immunity (T lymphocytes),
Humoral Immunity (B cells), and Accessory cells
(antigen-presenting cells).

46. ◼ The two major populations of lymphocytes —B
lymphocytes (B cells) of Humoral immunity and T
lymphocytes (T cells) of Cellular Immunity provide us
with our specific adaptive immunity
The adaptive immune system
◼ Specialization –the immune system responds in
distinct and special ways to different microbes,
maximizing the efficiency of antimicrobial defense
mechanisms. Thus, humoral immunity and cell mediated

47. immunity are elicited by different classes of microbes or
by the same microbe at different stages of infection
(extra cellular & intra cellular)
◼ Self –limitation- All normal immune responses returning
the immune system to its resting or basal state with time
after antigen stimulations, process called homeostasis.

49. Humoral defense
• Involves production of antibodies.
• Initial exposure to an antigen results in the production of low affinity antibodies
•Continued exposure to antigen leads to the production of high affinity
antibodies.
• In primary antibody response, B cells are activated to produce IgM antibody
• By 3-5 days, specific antibodies mainly of the IgM appear in serum and
concentration increases until a pick is reached in 10-14 days
• Antibody titre then fall to pre-immunization level after some weeks

50. Humoral defense
• Upon immunization, there is more rapid and extensive development of
antibody producing cells in regional lymph nodes and many of them undergo
isotope switch to produce IgG or other immunoglobulin classes of specific
antibodies.
• Antibodies function to inactivate viruses or bacteria toxins by blocking their
binding sites and label microorganisms for destruction by phagocytes or
complement- mediated lysis.

54. Summary of innate and adaptive immunity
Comparison of Innate and Adaptive Immunity
Innate Immunity Adaptive Immunity
• No time lag
• Not antigen specific
• No memory
• A lag period
• Antigen specific
• Development of
memory

55. Tissue Transplant
◼ Histocompatibility: Matching of donor and recipient
tissue to minimize rejection. Major Histocompatibility
Complex (MHC) plays a crucial role.
◼ Compatibility of RH and ABO blood group
◼ Rejection: Host immune system recognizes the
transplanted tissue as foreign and mounts an
immune response.

56. Hypersensitivity Reaction
◼ Hypersensitivity reactions are exaggerated or
inappropriate immune responses to antigens
(foreign substances) that can lead to tissue damage.
There are four types of hypersensitivity reactions:
Hypersensitivity reaction
◼ Type I (Immediate Hypersensitivity):
 Rapid onset (within minutes)
 Mediated by IgE antibodies

57.  Examples: Allergic reactions (e.g., hay fever, asthma,
anaphylaxis)
◼ Type II (Cytotoxic Hypersensitivity):
 Mediated by IgG or IgM antibodies
 Antibodies target antigens on host cells, leading to cell
destruction by complement activation or phagocytosis
 Examples: Blood transfusion reactions, autoimmune
hemolytic anemia
Hypersensitivity reaction
◼ Type III (Immune Complex-Mediated Hypersensitivity):

58.  Mediated by immune complexes (antigen -antibody complexes)
depositing in tissues and causing inflammation and tissue damage
 Examples: Systemic lupus erythematosus (SLE), rheumatoid arthritis
◼ Type IV (Delayed-Type Hypersensitivity):
 Delayed onset (hours to days)
 Mediated by T cells (specifically, CD4+ T cells or CD8+ T cells)
 Results in inflammation and tissue damage
 Examples: Contact dermatitis (e.g., poison ivy), Tuberculin skin test
reaction
Auto Immune Diseases
◼ Autoimmune diseases occur when the immune
system fails to distinguish between self and nonself

59. antigens, leading to an attack on the body's own
tissues.
◼ The exact cause of autoimmune diseases is not fully
understood, but factors such as genetics,
environmental triggers, and infections play a role.
Auto Immune Diseases
◼ Autoantibodies: Antibodies mistakenly produced by
the immune system that target selfantigens, leading
to tissue damage.

60. ◼ T Cell Dysfunction: Dysregulation of T cells,
including CD4+ T helper cells and CD8+ cytotoxic T
cells, which play a central role in orchestrating
immune responses.
◼ Examples: inflammatory bowel diseases, diabetes
type 1 etc.

61. Summary of innate and adaptive immunity
Infectious
Exposure
Innate Immunity
holds
Innate Immunity
Fails
Disease
Adaptive
Immune system
Recovery
Second Infectious
Exposure
Same organism
Adaptive Immunity
Specific memory
No
Disease

62. Adaptive and Innate - Interactions