Nursing college, Second stage
Microbiology
L12:
Dr.Nada Khazal K. Hendi
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
vertebrates .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).
1
Nursing college, Second stage
Microbiology
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 it‫ۥ‬s 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,
lysozyme, oleic acid on the skin in addition to blood, lymph and other body fluids
2
Nursing college, Second stage
Microbiology
Dr.Nada Khazal K. Hendi
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.
3
Nursing college, Second stage
Microbiology
Dr.Nada Khazal K. Hendi
Example of Innate (non specific) immunity
System/organ
Immune effectors mechanisms
Skin
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.
4
Nursing college, Second stage
Microbiology
Dr.Nada Khazal K. Hendi
 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 .
Acquired or adaptive (specific) immunity
the resistance, which absent at the time of first exposure to a pathogen, but develops after
being exposed to the pathogen is called acquired immunity. It includes specific cells of
the immune system that ate able recognize and response to the foreign materials. The
cells involved in this type of immunity are lymphocytes both T and B cells.
Properties of acquired or adaptive (specific) immunity
Also known as acquired immunity, resist a particular foreign agents, moreover, specific
immune response improve on repeated exposure to the same agents, many characteristic
distinguish specific immunity from non- specific immunity:
1. Specificity: specific activity for each type of pathogens.immunity is directed against
a particular pathogen or foreign substance.
2. Memory: when exposed to the same pathogen or substance the body reacts so
quickly that there is no notice able pathogenesis, Recognition to the specific sites on
the foreign substances (Ag) needs at first a certain time so innate immunity is faster
than specific immunity but the later is more effective and the program of the solid
immunity against infectious disease depend on the activation of specific immunity.
Response results in immunologic memory very important characteristic feature that
the concept of vaccination depends on
3. Diversity: the system is able to generate an enormous diversity of molecules such as
antibodies that recognize billions of different antigens.
4. Discrimination between self and non self. The specific immune system always
responds only to non self antigens thus, does not attack human itself .
5. Response is antigen dependent.
5
Nursing college, Second stage
Microbiology
Dr.Nada Khazal K. Hendi
6. the effectiveness toward antigens increases following subsequent exposure to the
same antigens. Thus second contact with the same antigens increases the immune
response through antibodies or sensitized memory cells.
Classification of acquired or adaptive (specific) immunity
According to the nature of components of immune mediated reactions:
A:Humoral immunity(HI): mediated by specific glycoproteins (immunoglobulins or Ab).
B: Cell mediated immunity (CMI): mediated by specific cells which are T lymphocytes.
Also, specific immunity can be classified according to the rout of acquirement into:
1. Natural immunity
A: passive (placental transfer of Ab).
B: Active (as response to the infection).
2.Artificial immunity
A: passive (administration of Ab e.g. antitoxin antibodies).
B: Active (vaccination: administration of attenuated live or killed foreign invaders to
stimulate the immune system).
1-Humoral (antibody – mediated ) immunity
It is antibody ( Abs.) dependent and relies upon body fluids especially the lymph
and blood plasma to spread Abs. around the body . The Abs. are produced by Blymphocyte and it is thought that processing of B-cell occurs in bone marrow and fetal
liver . There are five classes of Abs. each is called immunoglobulin as fallow:
IgA (15% of total Abs. count) found in mucous secretion of respiratory and digestive tract
, vagina and in colostrums the substance is produced before the milk after delivery will
protect the baby for about six months .
IgD
(less than 1%) appears to have a role in activating and suppressing lymphocyte
activity .
IgE
(less than 1%) it is mediator in allergic response , activate histamine secreting cells
and play role in parasitic infection .
6
Nursing college, Second stage
IgG
Microbiology
Dr.Nada Khazal K. Hendi
(75% of total count) stimulate phagocyte cells , activate the complement system and
neutralized toxins . It is the only Abs. that can cross the placenta and confer immunity on
the fetus.
IgM
(10% of total Abs.) this is the predominant early Abs. that activate in an initial
attack of Ag. Because of it is high number of antigen binding sites have 5 sites ( Fig.) ,this
is important in an initial activation of B –cells macrophage and complement system .
7
Nursing college, Second stage
Microbiology
Dr.Nada Khazal K. Hendi
Fig. sites of binding antibodies with antigens
Cell – mediated immunity
It is involved T- lymphocyte cell, that is originally derive from stem cells of the bone
marrow and then passes to the thymus gland in the chest , where they multiply. Cell –
mediated is based on the action of specific kinds of cell
T- lymphocyte that directly
attack cells infected with viruses or parasites , transplanted cells or organs and cancer cells
.T- lymphocyte can lyses these cells or release chemicals like cytokines that enhance
specific immunity and non- specific defenses such as phagocytes and inflammation.
The cells responsible for both specific and non- specific immunity are leukocytes
(meaning white cell) from the stem cells which migrate to the other body sites undergo
further development , some become residents within tissues while others circulate in body
fluids . In figure below there are different types of leukocyte :
LEUKOCYTES: White Blood Cells
Granular leukocytes (granules in
cytoplasm)
Nongranular leukocytes (do not have
granules in their cytoplasm)
non
Fig. Leukocytes types divisions
8


Nursing college, Second stage
Microbiology
Dr.Nada Khazal K. Hendi
1-Lymphoid cells
Lymphocyte are major cells of specific immune system , lymphocyte can be divided into
three population T, B and natural killer (NK) cells .
2- Mononuclear cells
There are two types of mononuclear : monocyte & macrophages are highly phagocytic were
engulfed & destroyed pathogenic M.O.
3- Granulocytes
Have irregular- shaped nuclei with 2-5 lobes and the cytoplasm matrix has granules contain
reactive substances which kill M.O. There are three types of granules : neutrophil , acidophile ,
basophile .
neutrophile
9
Nursing college, Second stage
Acidophile
Microbiology
Basophile
10
Dr.Nada Khazal K. Hendi