The immune system can be divided into three lines of defense against pathogens: 1. The first line of defense are physical and chemical barriers like the skin and mucous membranes that prevent pathogens from entering the body. 2. The second line of defense is the innate immune system, which includes non-specific cells and mechanisms like phagocytes and complement proteins that attack foreign substances. 3. The third line of defense involves adaptive immunity including B and T lymphocytes that produce antibodies and mount a specific immune response against pathogens.

1. Nutritional Immunology
-Lines of Defense
ROSHINA RABAIL
LECTURER, GOVERNMENT COLLEGE WOMEN UNIVERSITY, FAISALABAD, PAKIS TAN.
M.PHIL HUMAN NUTRITION AND DIETETICS
FORMER DIETITIAN CMH OKARA CANTT. & SHIFA INT. HOSPITAL ISLAMABAD
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2. Lines of Defense
The immune system can be divided into three basic lines of defense
against pathogenic infection:
◦ The first line of defense against infection are the surface barriers that prevent
the entry of pathogens into the body
◦ The second line of defense are the non-specific phagocytes and other internal
mechanisms that comprise innate immunity
◦ The third line of defense are the specific lymphocytes that produce antibodies
as part of the adaptive immune response
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3. Line of Defense
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4. FIRST LINE OF DEFENSE- SKIN AND PHYSICAL AND CHEMICAL BARRIERS
The primary defence against infectious disease are the surface barriers that
prevent pathogens from entering the body
Many of the body’s most effective defenses are nonspecific
These surface barriers include intact skin (protect external boundaries) and
mucous membranes (protect internal boundaries)
Both the skin and mucous membranes release chemical secretions which
restrict the growth of microbes on their surfaces
If pathogens cannot enter the host body, they cannot disrupt normal
physiological functions and cause disease
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5. Physical and
Chemical Defenses
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6. Physical and Chemical Defenses—The Skin and Mucosal Tissues
The structural integrity of tissue surfaces—barrier to penetration by microbes.
Intact surfaces prevent potential pathogens from adhering to surfaces Growing
at these sites such that they do not travel elsewhere in the Body—
COLONIZATION.
Damaged surfaces—abraded skin are often readily colonized promoting
invasion of this and other tissues
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7. Skin
Microorganisms normally Associated
with skin prevent Potential pathogens
from Colonizing
Sebaceous glands secrete Fatty acids
and lactic acid Which lower the skin pH
(pH 4-6)
Unbroken skin is a contiguous Barrier
The skin has a low moisture content
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8. Mucosal membranes
a. Ciliated epithelial cells lining the trachea remove microbes inhaled through the nose and
mouth.
b. Mucus secreted by these cells prevent the microbes from associating Too closely with the
cells
c. Cilia push microbes upwards until they are caught in oral secretions and expectorated or
swallowed.
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9. Normal Flora of the Gastrointestinal Tract
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10. Potential pathogens in the gastro-intestinal tract
The pH of the stomach is 2.0 which is too low for most pathogens
Pathogens must compete with the normal flora associated with the small and
large intestines. (pH 5 and 7, respectively)
The large intestines normally contain approx 1010 bacteria per gram of
content—establishment of pathogens difficult
Microbes have a difficult time adapting to abrupt changes in pH as they might
encounter as they pass through the GI tract.
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11. Lysozyme of the eye and kidney
Lysozyme constantly baths the kidney and the surface of the eye
(tears).
(also found with egg whites and the female urogenital tract, and
saliva)
Lysozyme breaks the glycosidic bonds between the NAG and NAM
that make up the backbone of peptidoglycan—causing bacteria to
lyse.
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12. Extracellular fluids
Blood plasma contains bacteriocidal substances
Blood proteins called beta-lysins bind to and disrupt the bacterial
cytoplasmic membrane—leads to leakage of the cytoplasmic
constituents and bacterial cell death
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13. Tissue Specificity
Organisms first adhere and colonize at the FIRST site of exposure
If this site is not compatible with their environmental or nutritional needs they
die.
EXAMPLE: Clostidium tetani—tetanus.
 Ingestion: The organism does not survive the low pH of the stomach
 Introduced into a deep wound: organism can grow in this anoxic
environment that has been created by localized tissue death
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14. ROSHINA RABAIL 14

15. Lines of Defense
•The immune system can be divided into three basic lines of defense
against pathogenic infection:
• The first line of defense against infection are the surface barriers that prevent
the entry of pathogens into the body
• The second line of defense are the non-specific phagocytes and other internal
mechanisms that comprise innate immunity
• The third line of defense are the specific lymphocytes that produce antibodies
as part of the adaptive immune response
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16. Line of Defence
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17. THE SECOND LINE OF DEFENSE-CELLULAR COUNTERATTACK
• A patrolling army of macrophages, neutrophils, and natural killer cells attacks
and destroys invading viruses and bacteria and eliminates infected cells.
• In addition, a system of proteins called complement may be activated to
destroy foreign cells, and body cells infected with a virus secrete proteins
called interferons that protect neighboring cells.
• The second line of defense against infection are the non-specific cellular and
molecular responses of the innate immune system
• These defenses do not differentiate between different types of pathogen and
respond the same way upon every infection
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18. THE SECOND LINE OF DEFENSE-CELLULAR COUNTERATTACK
•Phagocytic leukocytes migrate to infection sites and engulf foreign
bodies (dendritic cells then present antigens to lymphocytes)
•Inflammatory responses increase capillary permeability at infected
sites, recruiting leukocytes but leading to localised swelling
•Antimicrobial proteins (such as cytokines and complement proteins)
regulate immune activity within the body
•Fever increases body temperatures to activate heat-shock proteins
and suppress microbial growth and propagatio
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19. Cells of the Innate Immune System
Monocytes
differentiate into macrophages serve as antigen-presenting cells in the adaptive
immune responses
Phagocytes
Phagocytosis.
 Required to process and present antigen to immunocompetent T cells.
 Production of cytokines, such as IL-1 and TNF, which are roinflammatory
 Lyses tumor cells by secreting toxic metabolites and proteolytic enzymes
Examples of tissue macrophages are kuppfer cell of the liver, microglial cells of brain,
mesangial phagocyte of the kidney, alveolar macrophages of lungs and osteoclasts of
bone.
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20. ROSHINA RABAIL 20

21. NEUTROPHILS:
Mediate the earliest phase of inflammatory response and aids in phagocytosis.
The cytoplasm contains enzymes such as lysozyme, collagenase, elastase lactoferrin, acid hydrolase, and
myeloperoxidase and other microbicidal substances.
They also possess receptors for IgG antibody. These receptors enable neutrophils to participate in the
inflammatory response and phagocytosis.
EOSINOPHILS
They are phagocytic cells.
contains receptors for immunoglobulins, growth factors and complement components on the cell
surface
Their primary function may be secretion and extracellular killing rather than intracellular.
perform specialized function namely immediate hypersensitivity in response to parasites and protozoa.
secrete destructive enzymes such as acid phosphatase, peroxidases and proteinases and promotes
inflammation
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Cells of the Innate Immune System

22. BASOPHILS
Basophils contain several enzymes, histidine carboxylase.
release histamine, leukotrienes, and prostaglandins, chemicals that
promotes inflammation
Mast cell
Has inflammatory mediators such as histamine, eosinophils chemotactic
factor, neutrophil chemotactic factor and heparin and zinc ions.
It also synthesizes TNF and leukotriene C4.
These cells possess receptors for complement components (C3a and C5a) as
well as receptors for the antibody molecules, IgE and IgG
The stimulation of these receptors can result in activation and secretion of
vasoactive substances that increase vascular permeability and dilation.
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Cells of the Innate Immune System

23. THE THIRD LINE OF DEFENSE-THE IMMUNE RESPONSE
The final line of defence against infection are the lymphocytes that produce
antibodies to specific antigenic fragments
Each B cell produces a specific antibody, and the body has millions of different
B cells capable of detecting distinct antigens
Helper T cells regulate B cell activation, ensuring that antibodies are only mass-
produced at the appropriate times
Both B and T cells will differentiate to form memory cells after activation,
conferring long-term immunity to a particular pathogen
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24. THE THIRD LINE OF DEFENSE-THE IMMUNE RESPONSE
Antigens are molecules, usually foreign, that provoke a specific immune
attack. This immune attack may involve secreted proteins called antibodies, or
it may invoke a cell-mediated attack
Humoral immunity: lymphocytes called B cells respond to antigens by
producing proteins called antibodies. Antibody proteins are secreted into the
blood and other body fluids and thus provide humoral immunity (the term
humor here is used in its ancient sense, referring to a body fluid.) Other
lymphocytes
Cell-mediated immunity : called T cells do not secrete antibodies but instead
directly
Attack the cells that carry the specific antigens. These cells are thus described
as producing cell-mediated immunity.
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