Nursing college, Second stage
Microbiology
Dr.Nada Khazal K. Hendi
L12: :
Immunology
Immunology: is the study of host's defense mechanisms against disease, also study the
interaction between human and disease agents (pathogenic microbes)., it includes the
distinction between self and non self of immune response.
Immunity: refers to the general ability of the host to resist a particular infection or
disease.
Antibody (Ab): a protein present in the blood, tissue, fluid and mucous membrane of
vertebrate's produce as a result of interaction with an Ag. It has the ability to combine with
Ag that stimulated its production.
Antigen (Ag) or immunogen is it is a foreign substance such as protein (pathogen) that
reacts with Ab. Not all Ag induce Ab production.
Immune system
It is a complex network of specialized cells , organs and tissues evolved to defend the
body against attacks by foreign invaders .The organs involved the immune system are
called lymphoid organs, play a role in production and activate lymphocytes they are:• Bone morrow.
• Thymus (two lobes that join in front of the trachea).
• Lymph nodes (small organs shaped like beans located throughout the body) .
• Tonsils (two oval masses in the back of throat)
• Payer's patches (Lymphoid tissue in the small intestine).
• Lymphatic vessels (a network of channels throughout the body that carries
lymphocytes to the lymphoid tissue in the abdominal cavity).
• Spleen (a fist – size organ located in the abdominal cavity).
• Adenoid (two glands located at the back of the nasal passage).
General functions of immune system
1. Defense against foreign invaders.
2. Autotolerance (unresponsiveness to the self tissues).
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Microbiology
Nursing college, Second stage
Dr.Nada Khazal K. Hendi
3. Surveillance: recognition and clearance of internal antigens (old damaged, or
mutagenic cells).
Host resistance & Types of Immunity
The interaction between a host and microorganism is a dynamic process in which each
protagonist acts to maximize it ‫ۥ‬s survival , in some instances , after a M.O enters or
contacts a host a positive relationship occurs , while in other M.O produces deleterious
effects on the host , so , there are many factors influenced on host – microbe relationship
either directly such as nutrition , physiology , age and genetics or indirectly such as
personal hygiene , socioeconomic status etc. as a result of influenced on the immunity , for
example when the host is either very young or very old , sensitivity to infection increases.
To establish an infection, the pathogenic M.O must first overcome many surface barriers,
such as physicochemical barriers that are either directly antimicrobial or inhibit attachment
of M.O to the host. Any M.O can penetrate these barriers encounter two levels of
resistance. Immunity can be classified according to their specificity into:
1. Innate (non specific) immunity and
2. Acquired or adaptive (specific) immunity
1-Non- specific resistant (innate immunity)
The elements of the non specific immunity include:
A-Non – specific innate defenses
The body has a number of built in defense mechanisms which provide protection against
a wide range of pathogens , it is includes general mechanisms inherited as part of innate
structure and act as a first line of defenses called non - specific innate defenses such as:
1. Physical or Anatomical barriers
a- skin b- tears in eyes c- waxes in ears d- urine in bladder
respiratory system
e- cilia and mucous in
f- mucous membrane and peristalsis in gastrointestinal tract
and
intestinal movement g- saliva in mouth.
2. Chemical barriers
Mammalian host have numbers of chemical substances to combat the continuous on
sloughs of M.O, some of this chemicals like: gastric juice, salivary glycoprotein,
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Nursing college, Second stage
Dr.Nada Khazal K. Hendi
Microbiology
lysozyme, oleic acid on the skin in addition to blood, lymph and other body fluids contain
defensive chemicals such as bacteriocin and betalysine, fatty acids in sweat,
phospholipids, pH, defensins which are antimicrobial polypeptides secreted by wide
variety of host cells.
3. Physiologic barriers: fever response to infection inhibits growth of many microbes.
4. Biological factors: include the normal flora of the (skin, genitourinary tract, GIT) can
prevent the colonization of pathogenic microbes by secreting toxin substances or by
competing with pathogens for nutrient or attachment to host cells.
B-Non – specific cellular defense
In addition to non- specific innate defense, the body also has a range of different cell
types that involved in non – specific cellular defense as fallow:
a-Neutrophile
( 60-70% of WBC count)
b- Natural killer cell (5-8% of WBC count)
c- Macrophage
(5% of WBC count)
d - Eosinophile
(1.5% of WBC count)
Properties of Innate (non specific) immunity
1. Present at birth & does not improve on repeated contact with the same infectious agent.
2. Non specifically protects against foreign substances.
3. Response results in no immunologic memory.
4. Response is antigen- independent.
5. Inborn resistance.
6. Response is characterized by immediate maximal course and occurs at rapid rate.
7. Not needs for time of recognition or helping from other components of immune system.
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Nursing college, Second stage
Dr.Nada Khazal K. Hendi
Microbiology
Example of Innate (non specific) immunity
System/organ
Skin
Immune effectors mechanisms
Mechanically prevents entry of microbes. Sweat contain fatty acids
which denatures microbial cellular proteins
Saliva
Hydrolytic enzymes
Tears
Lysozymes
Lung
Cilia, lysozymes, surfactant (antimicrobial lipoproteins)
GIT
Gastric pH, bile acid, lysozymes, flusing normal flora
Genitourinary tract Low pH, normal bacterial flora
Blood
Phagocytosis, complement, acute phase proteins
Mucous
Mechanically prevent entry of microbes, normal bacterial flora
membranes
interferes with the attachment of pathogenic microbes to the
mucous membranes and consequently entry of pathogenic microbes
into body is prevented.
Inflammation
Inflammation is an important non – specific defense reaction to tissue injury or wound
caused by a pathogen. Acute inflammation is the immediate response of body to injury or
cell death, the gross features were described over many years ago and are still known as the
cardinal signs of inflammation, these signs include redness, warmth, pain, swelling and
altered function. During the acute Inflammation, the offending pathogen is neutralized and
eliminated by a series of events, the most important of which are the following:
• The increase in blood flow and capillary dilation bring into the area more antimicrobial
factors and leukocytes that destroy the pathogens.
• The rises in temperature stimulate the inflammation response and may inhibit microbial
growth.
• A fibrin clot often forms and may limit the spread of the invaders so that they remain
localized.
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Nursing college, Second stage
Dr.Nada Khazal K. Hendi
Microbiology
• Phagocytes collected an inflamed area and phagocytes the pathogen in addition to
chemicals stimulate the bone marrow to release neutrophile and increase the rate of
granulocyte production.
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