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Oily Fish
Species of fish which store fat throughout their flesh
(for example salmon, herring and mackerel)s.
Fatty Acids and the Immune System
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Oliguria
A urine volume insufficient to sustain life, usually less
then 400 ml per 24 hours.
Septic Shock
Opsonin
A molecule that binds to antigen and phagocyte to
enhance phagocytosis. C3b and C4b along with their
degradation products are opsonins derived from the
complement system. Immunoglobulins also function
as opsonins.
Complement, Classical Pathway/Alternative Pathway
Opsonins
All factors by which bacteria or other microorganism
are altered by the attachment to the surface so that they
are more readily and more efficiently engulfed by phagocytes, are collectively called Opsonins.
Respiratory Infections
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Organization for Economic Co-operation and Development, an international organization helping governments solve the economic, social and governance challenges of a globalized economy. Testing guidelines of
the OECD recommend procedures for testing chemicals.
Immunotoxicology
3
3
OECD
Infections with bacteria, viruses, fungi, or protozoa to
which individuals with a normal immune system are
not usually susceptible. That is, infections that are
caused by microbes that are not very infectious, but
that can be so when the normal immune system is not
functioning properly.
Lymphoma
Leukemia
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Diabetes and Diabetes Combined with Hypertension, Experimental Models for
Opportunistic infection
3
Obese Zucker rat
3
Opsonization
Oncogenes
Mutated genes that are the cause of a cancer. The normal gene is called the proto-oncogene. These genes
are usually involved in the regulation of cell growth
or survival or the intermediate steps in those processes.
Lymphoma
Leukemia
Phagocytosis of microorganisms such as bacteria can
be enhanced by binding of antibodies, complement
factors (mainly C3b), or blood plasma proteins,
which are also collectively termed opsonins. These
endogenous proteins cover a pathogen and thereby
make it “visible” for sentinel cells (macrophages, dendritic cells, or neutrophilic granulocytes) which posses
specific receptors for the opsonins.
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3
Opsonization and Phagocytosis
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3
3
3
Opsonization and Phagocytosis
Charles J Czuprynski
Department of Pathological Sciences
University of Wisconsin
2015 Linden Drive W
Madison, WI 53706
USA
dies) that are specific for antigenic determinants on
that organism, or with complement proteins (particularly C3b) deposited on the surface of the organism
via either the classical or alternative activation pathways. The presence of these plasma proteins on the
surface of the microbe facilitates their sequential interaction with immunoglobulin receptors (Fc receptors)
or complement receptors (CR) on the phagocyte surface. These interactions result in encirclement of the
particle by the cytoplasmic membrane of the phagocytic cell, until the particle is contained within a membrane-bound vacuole (phagosome) within the cell.
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Immune Response
Fish Immune System
Complement Deficiencies
Streptococcus Infection and Immunity
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Characteristics
In general, the term phagocytosis refers to ingestion of
microbes or other particles by professional phagocytic
cells. These include granulocytes (principally neutrophils) and monocytes in the bloodstream, and
mononuclear phagocytes ( macrophages) that are distributed throughout the various tissues of the body.
Opsonization of a microbe by immunoglobulins (antibodies) reflects a specific immune response against
antigenic epitopes on that microbe, as a result of natural infection or immunization, or a cross-reaction
with antibodies against related antigens. Activation
of the complement cascade on the surface of the microbe via the classical pathway, occurs following binding of certain immunoglobulin isotypes (usually IgG)
to the surface of the microbe. This event leads to deposition of the C1 complex, which has C3 convertase
activity and cleaves C3 to C3b on the surface of the
microbe. The alternative pathway of activation occurs
when a different C3 convertase (composed of C3 and
factor B) forms on the microbial surface. Once the IgG
or C3b are deposited on the microbial surface, they
can interact with specific receptors (Fc and CR, respectively) on the cytoplasmic membrane of phagocytic cells. There are subtypes of both receptors present
on various leukocyte populations, that may demonstrate either activating (immunoreceptor tyrosinebased activation motif or ITAM) or inhibitory (immunoreceptor tyrosine-based inhibition motif, or ITIM)
activity. Other plasma proteins that have been reported
to opsonize and facilitate ingestion of particles by phagocytic cells include fibronectin, fibrinogen, and Creactive protein. The interactions amongst plasma proteins and phagocytic cells provides the critical first line
of cellular defense in innate immunity against microbial infection.
Once it is internalized within the phagosome, the vacuole becomes acidified and the ingested microbe will
be exposed to a variety of antimicrobial compounds.
These include reactive oxygen intermediates and nitrogen intermediates that are produced in response to
activation of ITAM-containing Fc receptors, and antimicrobial proteins and peptides (e.g. lysozyme, defen3
ingestion, uptake, internalization
Definition
Opsonization is the process by which a foreign particle, particularly a microbe, is coated with plasma proteins (opsonins) so as to facilitate the attachment and
internalization of that particle by a professional phagocytic cell. In general, the process refers to coating of
the microbe with immunoglobulin molecules (antibo-
Opsonization and Phagocytosis. Figure 1 Simplified
overview of how opsonization with IgG and C3b
facilitates phagocytosis, phagolysosome formation, and
release of reactive oxygen intermediates, defensins
and other microbicidal peptides into the phagolysosome.
3
Synonyms
Oral Mucositis and Immunotoxicology
sins) that are present in preformed lysosomal granules
in the phagocytic cell. Following granule fusion, the
phagosome is referred to as a phagolysosome. Most
microbes cannot survive in the hostile environment of
the phagolysosome. Intracellular pathogens have
evolved strategies to circumvent formation of this hostile environment (e.g. inhibition of phagosome acidification or phagolysosome formation), or resistance
mechanisms to the toxic compounds contained within
the phagolysosome (e.g. production of catalase or superoxide dismutase to scavenge reactive oxygen intermediates).
Preclinical Relevance
Experimental assessment of the effects of potential
toxicants on innate immunity would include concerns
about inhibition of the ability of the exposed individual to produce immunoglobulins that can opsonize
pathogenic microbes, and the ability of their granulocytes and mononuclear phagocytes to ingest and kill
the opsonized microorganisms. Various simple assays
can be performed to assess phagocytosis of bacteria,
yeast cells, or other particles. Opsonins (e.g. serum as
a source of immunoglobulins and complement) might
be added to facilitate evaluation of the phagocytic
function of granulocytes and mononuclear phagocytes.
Fluorescent beads (either opsonized or uncoated) can
be used to evaluate phagocytosis by microscopy or
flow cytometry.
489
duction of immunoglobulins or other plasma proteins
required for opsonization of microbes. Although assessment of opsonization is not frequently done in a
regulatory situation, production of immunoglobulins,
as assessed either by ELISA or a plaque-forming cell
assay, is heavily relied upon for assessment of potential immunotoxicants. If a weak antibody response
occurred following toxin exposure, it might indicate
a potential for decreased resistance against extracellular pathogenic microbes that must be opsonized, ingested, and killed by phagocytic cells. The draft EPA
Health Effects Test Guidelines (OPPTS 870.1350) for
Acute Inhalation Toxicity with Histopathology include
assessment of phagocytic activity by alveolar lavage
macrophages using a fluorescent bead assay and microscopy.
References
1. Aderem AA, Underhill DM (1999) Mechanisms of
phagocytosis in macrophages. Ann Rev Immunol
17:593–623
2. Janeway CA, Travers P, Walport M, Shlomchik M (2001)
Immunobiology. Garland Publishing, New York, pp 24,
39–40, 49, 55–56, 371–373
3. Rosenberger CM, Finlay BB (2003) Phagocyte sabotage:
disruption of macrophage signaling by bacterial pathogens. Nat Rev Mol Cell Biol 4:385–396
Oral Mucositis and Immunotoxicology
Relevance to Humans
Phagocytic cells are essential for innate immunity
against microbial infection. Individuals afflicted with
genetically determined defects in their phagocytic cells
often experience significant problems in controlling
infectious agents. In some instances, the defect may
be of sufficient severity to cause repeated severe infections or premature death. There is concern that toxicants in the environment might alter the ability of
humans to produce, mobilize, and regulate the activity
of these phagocytic cells, and by so doing render individuals susceptible to infectious diseases. An additional concern for inhaled particulate toxicants is that
their ingestion by phagocytic cells in the lung might
elicit release of inflammatory mediators (e.g. cytokines, eicosanoids) that could damage nearby cells,
or attract inflammatory leukocytes that trigger hypersensitivity responses.
Regulatory Environment
Assessment of phagocytic cells is not universally required as part of the assessment of immune function.
Nonetheless, it is frequently listed on tiers of immune
function assays, and its assessment may be prudent or
required if the compound in question is known to have
an adverse effect on phagocytic cells, or on the pro-
Gary J Rosenthal
Drug Development
RxKinetix Inc.
1172 Century Drive, Ste # 260
Louisville, CO 80027
USA
Synonyms
Mucositis, stomatitis, ulcerative mucositis, ulcerative
stomatitis, radiation mucositis, oral ulcer
Definition
Oral mucositis is a frequent toxicological complication
of high-dose chemotherapy as well as head and neck
radiotherapy. This insidious condition manifests as inflammation of the moist mucosal lining the mouth and
back of the throat and ranges from redness to severe
ulceration over vast portions of the region. Symptoms
of oral mucositis vary from local pain and discomfort
to the inability to chew and/or swallow food or fluids,
or to communicate.
Characteristics
Oral mucositis induced from either chemotherapy or
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490
Oral Mucositis and Immunotoxicology
radiotherapy is characterized by painful and often incapacitating ulcerative lesions of the oropharyngeal
mucosa (1). Chemotherapy-induced mucositis often
presents as lesions involving the buccal and tongue
mucosa, the soft palate, and the floor of the mouth.
In contrast to this broad area of injury associated with
chemotherapy, patients being treated for head and neck
cancers with ionizing radiation manifest mucositis on
those oral mucosal sites that lie in the direct path of
radiation beam. The targeted oropharyngeal mucosa is
lined by mucus membranes with a high mitotic index
and is exceptionally sensitive to the antiproliferative
effects of chemotherapy and radiotherapy.
At the tissue and cellular level, oral mucositis manifests initially as hypoplasia and destruction of superficial epithelial cells along with a lack of cell renewal.
The subsequent erythematous areas proceed to desquamation and eventually ulcers covered by an exudate.
From the host defense perspective, cancer treatment
and resultant oral ulcers serve to weaken the defense
system of the lining of the mouth leading to marked
local infections. In addition, the potential for systemic
infection due to opportunistic and acquired oral flora
has been documented in cancer patients. This further
complicates the already challenging health status of
immunosuppressed patients where morbidity and mortality due to infection is of prime concern. While not
considered life-threatening to the extent that chemotherapy-induced myelosuppression has historically
been, oral mucositis is often identified by cancer patients as the single worst side effect of therapy. Symptoms may be so severe that they may limit a patient’s
ability to tolerate their chemotherapy or radiotherapy,
resulting in delayed or shortened treatment and limited
efficacy (2).
The early understanding of mucositis was of a disorder
that simply resulted from non-specific toxicity of chemotherapy or radiotherapy against the basal epithelium. More recent research has broadened our understanding to suggest a more complex pathology with
multifaceted interactions between connective tissue,
endothelium and epithelium, myelosuppression and
the oral microenviroment. A conceptual model for
oral mucositis outlining the probable pathophysiology
was published by Sonis in 1998 (3). In this model,
mucositis is broken down into four phases (also see
Figure 1):
* inflammatory/vascular phase
* epithelial phase
* ulcerative/bacteriological phase
* healing phase.
Inflammatory/Vascular Phase
In this early phase, chemotherapy or radiotherapy directly or indirectly induce events leading to local inflammatory events, including reactive oxygen-induced
cell damage, NF-κB/early response gene activation,
and proinflammatory cytokine induction, all of
which serve as a foundation for local tissue damage
and initiate the events leading to development of mucositis.
Epithelial Phase
Dividing cells of the epithelium begin to atrophy and
cell renewal is diminished in the face of any continued
antiproliferative cancer therapy. Inflammatory events
serve to augment the negative effects of tissue destruction.
Ulcerative/Bacteriological Phase
This is generally considered to be the most symptomatic phase with ulcerative erosions of the mucosa and
an altered opportunistic microbial microenviroment.
Healing Phase
This involves renewal of the epithelial cell population,
re-establishment of microbial homeostasis and local
immune function.
While oral mucositis is biologically complex and progresses as a continuum of these phases, the depiction
outlined by Sonis in 1998 allows a focus on the characteristic and likely primary events of the disorder as it
progresses from initiation to healing. Research conducted over the last 5 years (4,5) has served to add
support for the model put forth by Sonis and elucidates
in greater detail the cellular and subcellular events
associated with oral mucositis. Considering the involvement of reactive oxygen species (ROS) in mediating
other manifestations of chemotherapy or radiation toxicity, it seems likely that ROS play a role in the initiation and progression of mucosal injury (5).
Preclinical Relevance
Oral mucositis remains under extensive laboratory investigation. Animal models of mucositis have been
developed in a variety of species using radiation
alone or both chemotherapy and radiation protocols.
Possessing a cheek pouch accessible to treatment and
observation, the hamster has provided much of the
currently available preclinical information, though rodents have also been used with some success. Critical
understanding into the roles of mucosal immune dysregulation and wound healing are imperative areas of
preclinical research that will improve prospects for
effective prophylactic or treatment strategies.
Relevance to Humans
Myelosuppression was previously the major dose-limiting toxicity associated with of cancer therapies. With
therapeutic advances in the 1980s relative to infection
prevention and reduced myelosuppression via growth
factors such as granulocyte colony stimulating factor
Oral Ulcer
491
Oral Mucositis and Immunotoxicology. Figure 1 A conceptual model for oral mucositis outlining the probable
pathophysiology.
Adapted from Sonis (1998).
Regulatory Environment
A plethora of approaches have undergone clinical assessment around the world with no single approach
showing any consistent benefit. Currently no medication is approved by the Food and Drug Administration
(FDA) to prevent or treat oral mucositis. While clinical
trials investigating a variety of novel approaches continue, most patients and clinics manage symptoms
with morphine or other narcotic analgesics, with
mouth rinses, changes in diet, and cold liquids.
The FDA recognizes that oral mucositis is a serious
illness that needs to be addressed expeditiously and as
such has granted Fast Track designation to some candidate therapeutics in clinical development. Fast Track
designation is intended to expedite the regulatory re-
view and approval process for a product and claim that
addresses a significant unmet medical need.
References
1. Berger AJ, Kilroy TJ (1997) Oral complications. In:
Devita VT, Hellman S, Rosenberg SA (eds) Cancer
Principles and Practice of Oncology, 5th ed. Lippincott
Williams & Wilkins, Philadelphia, pp 2714–2725
2. Ohrn K, Sjoden P, Wahlin Y, Elf M (2001) Oral health
and quality of life among patients with head and neck
cancer or hematological malignancies. Supp Care Canc
9:528–538
3. Sonis ST (1998) Mucositis as a biological process: a new
hypothesis for the development of chemotherapy-induced
stomatotoxicity. Oral Oncol 34:39–43
4. Sonis ST, Scherer J, Phelan S et al. (2002) The gene
expression sequence of radiated mucosa in an animal
mucositis model. Cell Prolif 35 (Suppl 1):93–102
5. Blonder JM, Etter J, Samaniego A et al. (2001) Topical
bioadhesive antioxidants reduce the severity of experimental radiation induced oral mucositis. Proc Amer Soc
Clin Oncol 20:1606
Oral Ulcer
3
(G-CSF), thrombopoietin and erythropoietin, non-hematologic toxicities have now become significant
dose-limiting concerns. Of these non-hematologic
toxicities, oral mucositis has emerged as one of the
most problematic toxicities associated with current
therapeutic regimens with direct impacts on cure
rates and long-term survival (2).
Considering the frequency of oral mucositis, which is
determined by the type of cancer therapy ( e.g. approximately 40% in patients treated with systemic chemotherapy to nearly 100% of patients treated for head
and neck cancer), this unmet clinical need remains an
active area of clinical investigation.
Oral Mucositis and Immunotoxicology
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Organ-Specific Autoimmunity
Organ-Specific Autoimmunity
Autoimmune disease which affects a single organ in
the body such as the pancreas in type 1 diabetes.
Systemic Autoimmunity
Oryctolagus cuniculus
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492
Rabbit Immune System
3
Oxidative Stress
Organogenesis
The formation of the various organs of the body from
embryonic tissues during gestation.
Developmental Immunotoxicology
3
Organotypic Murine or Human Skin
Explant System
Oxidants released by phagocytes such as neutrophils
or macrophages play an important role in early immune defense against pathogens. Free radicals are
any atom that contain one or more orbital electrons
with unpaired spin states. Some radical species are
very reactive with other biomolecules (proteins,
DNA) and others, like the normal triplet state of molecular oxygen, are relatively inert. Cells have multiple
protective mechanisms against oxidative stress, e.g.
protective agents like antioxidants to prevent cell damage.
Rodents, Inbred Strains
3
Three-Dimensional Human Skin/Epidermal Models
and Organotypic Human and Murine Skin Explant
Systems
3
Oxy-PAH
A birth defect in which the palate and/or associated
structures fail to close along the midline during fetal
development. Cleft palate is an orofacial cleft defect.
Birth Defects, Immune Protection Against
3
Orofacial Cleft
Polycyclic Aromatic Hydrocarbons (PAHs) and the
Immune System
3