Download acquired immunity

Definitions
Immune -Exempt from the pathogen.
Immunology is used to mean the study of defense
mechanisms against infectious disease.
√ Specific
√ Non-specific
• innate or natural immunity: attributed to inherited
ability to produce antibodies without stimulation by
antigens
• acquired immunity: host is stimulated by contact
with antigens
Table 1
Non-specific Immunity
Specific Immunity
Response is antigen-independent
Response is antigen-dependent
There is immediate maximal response
There is a lag time between exposure and
maximal response
Not antigen-specific
Antigen-specific
Exposure results in no immunologic memory
Exposure results in immunologic memory
Introduction
• Fish is a heterogenous group of organisms
that include agnathans(lampreys and
myxines),condryctians(sharks and
rays),Teleosteans(bony fish).
• Fish and mammals shows some similarities
and some diffrences regarding immune
function.
Immune Response in Fish
• Fish are the most primitive vertebrates, but had to
develop an immune system for protection
• the only exception was cold water species: due to
low bacterial generation time at lower temperatures
• those living under schooling conditions and in warm
environments needed a highly developed response
• all fish pathogens contain antigens: viral particles,
bacteria, fungi, toxins and animal parasites
Response of Fish Following an
Encounter with a Pathogen
Fish Contacts
Pathogen
Innate Immunity
Failure
(Disease and
Death)
Humoral Response
(Extracellular
Pathogens and Toxins)
Initiation and Instruction of
the Specific Immune
Response
Acquired Immunity,
Immunologic Memory,
and Protection (Survival)
Success (No
Disease or
Infection)
Cell-Mediated Immune
Response
(Intracellular
Pathogens and
Viruses)
Non-specific defence mechanisms
• External barriers
Mucus
Skin
Lysozyme
Mucus
• Mucus which by entrapping micro organisms
and continuously inhibits colonization of the
integument.
• The rate of mucus production in fish can be
increased in the response to infection.
• Mucus of the fish is toxic to certain micro
organisms.
Skin
• Active immune responses occurring in the skin.
• The epidermal integrity is vital to fish in
maintaining osmotic balance & excluding micro
organisms.
• Ig is present in low concentration in skin mucus.
• lymphocytes, plasma cells & macrophages
present in the epidermis of fish.
Lysozymes
• Lysozyme is one of the most studied innate
responses in fish.
• It can act on the peptidoglycan layer of the
bacterial cell walls and resulting in the lysis
of the bacteria.
• Lysozyme response in fish is very rapid not
only related to bacteria,but also to other
alarm situation such as after stress
Phagocytic activation
• Macrophages and neutrophils can be enhanced
in two differents ways
Opsonins
Lymphokines
Opsonins:
An opsonin is any molecule that acts as a binding
enhancer for the process of phagocytosis.
Lymphokines:
Lymphokines are a subset of cytokines that are
produced by a type of immune cell known as a
lymphocyte.
Opsonins
• The alternative complement pathway can
be activated in normal serum by
pathogen(bacteria).
• Then more attach to phagocytic cell
resulting in enhancing phagocytosis.
Cont…
• Fish antibody seems to have weak opsoniting
activity but in the presence of complemet,
opsonization is strong because activation of the
classical complement path way.
• CRP&MBP have also been reported to have
opsonizing effect in fish.
Lymphokines
• Macrophages are able to kill pathogen or multiply
within normal macrophages respectively.
• The lymphokine responsible for this activation is
known as macrophages activating factor.
• It’s produced by fish T lymphocytes following
exposure to specific antigen.
Immune Response Sequence: 1
Begins when macrophage
encounters this non-self entity
(e.g., virus): macrophage literally
“eats” the substance, digests it and
displays pieces of the invader on
its surface. These pieces are
antigens.
Meanwhile, other viral particles are
at work, infecting nearby host cells.
Immune Response Sequence: 2
Antigenic fragments alert a
specific type of T lymphocyte
(“helper” T) to begin
choreographed attack of
intruder
Helper recognizes antigen
particles and binds to the
macrophage via an antigen
receptor
Helper T cells are unique to a
specific antigen
Immune Response Sequence: 3
This binding stimulates
production of chemical
substances such as
interleukin-1 (IL-1), tumor
necrosis factor (TNF) by
macrophage
Helper T cells generates
interleukin-2 and gamma
interferon (IFN-y)
All substances facilitate
intercellular communication
Immune Response Sequence: 4
As mentioned IL-2 instructs helper
T’s and “killer T’s” to multiply
Proliferating helper T’s release
substances that cause B cells
(another type of lymphocyte) to
multiply and produce antibodies
Meanwhile, many invader cells
have been consumed by
macrophages, but other “daughter”
viral particles have escaped and
are infecting other cells
Immune Response Sequence: 5
Killer T cells start shooting “holes” in
the surface of infected host cells
Antibodies released by B cells bind in
a lock-and-key fashion to antigens on
the surface of invaders that have
escaped macrophages (Ag-Ab
complex).
Makes it easier for macrophages and
special killer lymphocytes to destroy
unwelcomed entities.
Binding of antibodies with antigens
signals release of a blood
component, complement, to puncture
virus membrane (death)
Natural Cytotoxic Cells(NCC)
• NCC cells similar properties to NK cells.
• The fish NCC cells morphologically resemble
agranular lymphocytes or monocytes. Role in
defense mechanisms.
• They may be important protection against viral
parasitic & neoplastic disease.
Eosinophiles, Basophils & Mast cells
• Some fish species posses blood granulocytes
with eosinophilic or basophilic granules and
basophils.
• Many species posses eosinophil granular cells in
connective tissues in the skin and gills or
intestinal wall.
• Mast cells release of vasoactive amines.
• Fish do not posses IgE
Eosinophil, Basophil & Mast cell
Specific defence mehanisms
• Specific defense mechanisms are two
types.They are
1. Humoral immunity.
2. Cell mediated immunity.
Humoral Immunity in Fish
• Defined: the antibody response to foreign antigens
• Fish posses B-cells (surface immunoglobulin-positive
cells), similar to mammals in structure
• Surface IgM of B-cells serves as receptor for antigen
recognition and is of same specificity as the antibody
molecule that will be produced (Janeway and
Travers, 1994)
• Unlike crustaceans, fish possess immunologic
memory (Arkoosh and Kaattari, 1991)
• Their primary and memory response both use the
same IgM molecule, with eight antigen binding sites,
a potent activator of complement
Cell-Mediated Immunity in Fish
• Used to eliminate intracellular pathogens (e.g.,
bacteria, virus, parasites)
• Relies on contact of the foreign invader with the
subsequent presentation of an antigen having the
same major histocompatability complex (MHC I or II)
to T-helper cells (REM?)
• Once T-helper cells are stimulated, the produce
cytokines that result in stimulation of effector cells
(cytotoxic lymphocytes) or macrophages
• Cytokines stimulate aforementioned cells and also
recruit new cells to the area, activate them
• Work quite well against bacteria, important against
Edwardsiella ictaluri (Shoemaker, et al., 1999)
Lymphoid organs
Immune Tissues and Organs
• Most important immunocompetent organs: thymus,
kidney (head, trunk), spleen and liver
• Immune tissues in these organs not well defined
(Manning, 1994)
• Thymus: develops T-lymphocytes (helpers, killers;
similar to other vert’s), indirect evidence
• Kidney: important in both immunity and
hematopoiesis, site of blood cell differentiation
o
o
Early immune response handled by entire kidney
With maturity, anterior used for immune response; posterior
for blood filtration, urinary activities
Immune Tissues and Organs
• Kidney (cont.):
o blood flows slowly through kidney and
antigens are “trapped” or exposed to
reticular cells, macrophages, lymphocytes
o Anterior is where “memory” occurs
(Secombs et al., 1982)
• Spleen: secondary to kidney, involved in
immune reactivity and blood cell formation,
contains lymphocytes and macrophages
• Liver: could be involved in production of
components of the complement cascade,
important in resistance; not real clear
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