Class By:
Aneetta Zachariah
⦿Definition
⦿InnateImmunity
⦿Types of Innate Immunity
⦿Factors affecting Innate Immunity
⦿Mechanism
⦿ Immunity is defined as the resistance exhibited
by the host against micro-organisms or any
foreign substances
⦿ Immunity is classified into two:-
1.Innate Immunity : present from birth
2.Acquired or Adaptive Immunity : acquired
during the course of the life
⦿ Definition: It is an inborn resistance possessed
by an individual against infections right from
the birth, due to his genetic or constitutional
makeup
⦿ First line of host defence against infections
⦿ Independent of prior exposure to the microbes
⦿ Cells of innate immunity are non specific in
their action
⦿ Innate Immunity does not have a memory
component
1.Species Immunity
➢ Resistance to a pathogen shown by all members of
a particular species
➢ E.g. B.anthracis infects human beings but not
chickens
2. Racial Immunity
➢ Within one species, different races may exhibit
differences in susceptibility or resistance to
infections
➢ E.g. Algerian sheep is highly resistant to anthrax
which is a common disease of their races of sheep
3. Individual Immunity
➢ Resistance to infections varies with different
individuals of same race and species
➢ It is determined by various factors such as health
status, nutritional status, personal hygiene, genetic
differences
➢ E.g. Individual with genetic deficiency of glucse-6-
phosphate dehydrogenase are resistant to malaria
1.Age
➢ The two extremes of life(foetus and old age) are
highly susceptible to various infections
➢ In foetus, the immune system is immature and in
case of old age ,there is gradual waning of immune
responses
➢ The foetus in-utero is protected from maternal
infections through the placental barriers.
➢ Exceptions are some pathogens such as rubella
Toxoplasma gondii cross this barrier and lead to
congenital malformations
2.Hormones
➢ Hormonal disorders such as diabetes mellitus,
adrenal dysfunction and hypothyroidism enhance
susceptibility to infections
➢ Staphylococcal sepsis is more
common in diabetes which may
be associated with increased level
of carbohydrates
➢ The elevated steroid level during pregnancy is
related to higher susceptibility of pregnant
women to many infections
3.Nutrition
➢ Malnutrition lead to bacterial
infections
➢ Both humoral and cell mediated
immune responses are reduced in
malnutrition
1.EPITHELIAL SURFACES
i) Skin
➢ Act as mechanical barrier to microorganisms and
provide bactericidal secretions
➢ High concentration of salt in drying sweat,
sebaceous secretions will produce bactericidal
activity
➢ The skin may freed of transient flora but resident
flora present on skin is not easily removed
➢ The resident bacterial flora of skin and mucous
surfaces help to prevent colonization by
pathogens
ii) Respiratory Tract
Inhaled particles are trapped on moist mucus membrane
surfaces of nasal passages
Particles are trapped by mucous secretions in the
respiratory tract
Hair like cilia drives the particles towards the throat,
where they are ingested or coughed out
iii) Intestinal Tract
➢ Mouth will produce saliva(inhibitory effect) to
many microorganisms
➢ Some pathogens may be swallowed are destroyed
by acidic pH of gastric juices
iv) Conjunctiva
➢ Tears have major role by flushing away bacteria
and other dust particles
➢ Lysozymes present in tears contain antibacterial
substances
v) Genitourinary Tract
➢ Flushing action of urine eliminates bacteria from
urethra
➢ Acidic pH of vaginal secretion in females renders
vagina free of many pathogens
2. ANTIBACTERIAL SUBSTANCES
➢ Present in blood and tissues
➢ Substances are properdin , complement ,
lysozymes , betalysin, polypeptides and interferon
which produce antiviral activity
3.CELLULAR FACTORS
Infective agent invades tissues or epithelial surfaces
Exudative inflammatory reaction occur
Accumulation of phagocytes at the site of infection
Deposition of fibrin which entangles the organism
and act as barrier to spread of infection
PHAGOCYTOSIS
4.INFLAMMATION
➢ Tissue injury or irritation ,initiated by the entry of
pathogens or other irritants may result in
inflammation
➢ Inflammation leads to vasodilation ,increased
vascular permeability and cellular infiltration
5. FEVER
➢ Rise in temperature following infection is natural
defence mechanism
➢ It destroys the infective material
➢ Fever stimulates the production of interferon which
helps in recovery from viral infections
6. ACUTE PHASE REACTANT PROTEINS(APRs)
➢ They are the proteins synthesized by liver at steady
concentration, but their synthesis either increases
or decreases during acute inflammatory conditions
➢ It can also synthesized by endothelial cells,
fibroblast,monocytes and adipocytes
➢ Positive APRs: They are proteins whose levels are
increased during acute inflammation
➢ Negative APRs: They are proteins whose levels
are decreased during acute inflammation .It create
negative feedback that stimulates liver to produce
positive APCs
➢ APCs have various antimicrobial and anti-
inflammatory activities
❖ C – Reactive Protein(CRP)
✓ Rise in acute inflammatory condition
✓ Belongs to beta globulin family
✓ It precipitates with C- carbohydrate antigen f
pneumococcus
✓ Following an injury or inflammation, the CRP level
starts increases by 6 hours, doubles every 8 hr ,
reaches its peak by 48 hr
✓ Insignificant increase of CRP(‹1 mg/dL)-heavy
exercise. common cold and pregnancy
✓ Moderate increase(1-10 mg/dL)-bronchitis,
cystitis, pancreatitis, myocardial infarction
✓ Marked increase of CRP(›10 mg/dL)-acute
bacterial infections, major trauma
of Medical Microbiology, 3rd edition,
⦿ Essentials
by Apurba S Sastry
⦿ Textbook of Microbiology ,C.P.Baveja
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