10/30/2024
Chapter 5: Innate Immunity
Lecture 8: Oct 01, 2024
o First line of defense
- Concept of Immunity: Innate and Adaptive
- Innate immunity by Skin, Mucous membrane,
normal microbiota.
Ref: 1. Wikipedia,
2. Immunology-Kuby 5th Edition,
3. Immunology 7th Ed, -Roitt
4. Microbiology-Tortora and Funke, Chap 16
Concept of Immunity
Ref: Microbiology- Totora, Chap 16
o When microbes attack our bodies, we defend ourselves by
utilizing our various mechanisms of immunity.
o In general, there are two types of immunity: innate and
adaptive.
Innate immunity
o Innate immunity refers to defenses that are present at birth.
o They are always present and available to provide rapid
responses to protect us against disease.
o Innate immunity does not involve specific recognition of a
microbe.
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Concept of Immunity
Ref: Microbiology- Tortora, Chap 16
Innate immunity
o Further, innate immunity does not have a memory response,
that is, a more rapid and stronger immune reaction to the
same microbe at a later date.
o Among the components of innate immunity are the first line
of defense (skin and mucous membranes) and the
second line of defense (natural killer cells and
phagocytes, inflammation, fever, and antimicrobial
substances).
o Innate immune responses represent immunity's early-
warning system and are designed to prevent microbes from
gaining access into the body and to help eliminate those that
do gain access.
Concept of Immunity
Adaptive immunity
o Adaptive immunity is based on a specific response to a
specific microbe once a microbe has breached the innate
immunity defenses.
o It adapts or adjusts to handle a particular microbe.
o Unlike innate immunity, adaptive immunity is slower to
respond, but it does have a memory component.
o Adaptive immunity involves lymphocytes called T cells (T
lymphocytes) and B cells (B lymphocytes) and will be
discussed later.
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Innate Immunity:
o Innate immunity is resistance that is pre-existing and is
not acquired through contact with a nonself (foreign) entity
known as an antigen.
o It is nonspecific and includes barriers to infectious agents—
eg, skin and mucous membranes, phagocytic cells,
inflammatory mediators, and complement components.
o It may vary with age and with hormonal or metabolic activity.
Adaptive Immunity:
o Adaptive immunity, which occurs after exposure to an
antigen (eg, an infectious agent) is specific and is mediated
by either antibody or lymphoid cells.
o It can be passive or active.
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The immune system
Immune system
Innate (non-specific) immunity Adaptive (specific) immunity
• Anatomic barriers (Skin,mucous •Antigen specificity
membranes)
•Diversity
• Physological barriers
(temperature, pH) •Immunological memory
• Phagocytic Barriers (cells that eat •Self/nonself recognition
invaders)
• Inflammatory barriers (redness,
swelling, heat and pain)
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Mechanisms of Innate Immunity
o The simplest way to avoid infection is to prevent the
microorganisms from gaining access to the body
Physiologic Barriers at the Portal of Entry
The Skin
o The skin consists of two distinct layers:
- a thinner outer layer—the epidermis—and a
- thicker layer—the dermis.
o The epidermis contains several layers of tightly packed
epithelial cells. The outer epidermal layer consists of dead
cells and is filled with a waterproofing protein called
keratinacids in sebaceous secretions. The periodic
shedding of the top layer helps remove microbes at the
surface.
Mechanisms of Innate Immunity
The Skin
o When the skin is moist, as in hot, humid climates, skin
infections are quite common, especially fungal infections
such as athlete's foot.
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Physiologic Barriers at the Portal of Entry : Skin
o The dermis, which is composed of connective tissue,
contains blood vessels, hair follicles, sebaceous glands,
and sweat glands.
o This arrangement permits defensive cells to move from
blood into tissues during inflammation.
o The major line of defense is of course the skin which, when
intact, is impermeable to most infectious agents; when
there is skin loss, as for example in burns, infection
becomes a major problem.
Physiologic Barriers at the Portal of Entry : Skin
o Few microorganisms are capable of penetrating intact skin,
but many can enter sweat or sebaceous glands and hair
follicles and establish themselves there.
o Sweat and sebaceous secretions—by virtue of their acid
pH and certain chemical substances (especially fatty
acids)—have antimicrobial properties that tend to
eliminate pathogenic organisms.
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Physiologic Barriers at the Portal of Entry : Skin
o Lysozyme, an enzyme that dissolves some bacterial cell
walls, is present on the skin and can help provide protection
against some microorganisms.
o Lysozyme is also present in tears and in respiratory and
cervical secretions.
o Skin resistance may vary with age. For example, children
are highly susceptible to ringworm infection.
o After puberty, resistance to such fungi increases markedly
with the increased content of saturated fatty acids in
sebaceous secretions.
Barriers at the Portal of Entry: Mucous Membranes
o Mucus, secreted by the membranes lining the inner
surfaces of the body, acts as a protective barrier to block
the adherence of bacteria to epithelial cells.
o Microbial and other foreign particles trapped within the
adhesive mucus are removed by mechanical stratagems
such as ciliary movement, coughing and sneezing.
o Among other mechanical factors which help protect the
epithelial surfaces, one should also include the washing
action of tears, saliva and urine.
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Barriers at the Portal of Entry: Mucous Membranes
o In the respiratory tract, a film of mucus covers the surface
and is constantly being driven upward by ciliated cells
toward the natural orifices. Bacteria tend to stick to this film.
In addition, mucus and tears contain lysozyme and other
substances with antimicrobial properties.
o In the gastrointestinal tract, several systems function to
inactivate bacteria: Saliva contains numerous hydrolytic
enzymes; the acidity of the stomach kills many ingested
bacteria (eg, V cholerae); and the small intestine contains
many proteolytic enzymes and active macrophages.
o For some microorganisms, the first step in infection is their
attachment to surface epithelial cells by means of adhesive
bacterial surface proteins. If such cells have IgA antibody
that can prevent bacterial attachment.
Barriers at the Portal of Entry: Mucous Membranes
o Most mucous membranes of the body carry a constant
normal microbial flora that itself opposes establishment of
pathogenic microorganisms ("bacterial interference"). For
example, in the adult vagina, an acid pH is maintained by
normal lactobacilli, inhibiting establishment of yeasts,
anaerobes, and gram-negative bacteria.
o Many of the secreted body fluids contain bactericidal
components, such as acid in gastric juice, spermine and
zinc in semen, lactoperoxidase in milk and lysozyme in
tears, nasal secretions and saliva.
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Chapter 5: Innate Immunity
Lecture 8: Oct 01, 2024
o First line of defense
- Concept of Immunity: Innate and Adaptive
- Innate immunity by Skin, Mucous membrane,
normal microbiota.
Ref: 1. Wikipedia,
2. Immunology-Kuby 5th Edition,
3. Immunology 7th Ed, -Roitt
4. Microbiology-Tortora and Funke, Chap 16
