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ontogeny 542 oral immunology
ontogeny
The development of an individual organism from conception
to maturity.
open reading frame (ORF)
A length of RNA or DNA that encodes a protein and may
signal the identification of a protein not described previously.
An ORF begins with a start codon, ends at a stop
codon, and lacks a termination codon.
opisthorchiasis (clonorchiasis) immunity
Antibodies synthesized in patients with opisthorchiasis (or
chlonorchiasis) react with the various developmental stages
of the parasites. Stage-specific and cross reactive common
antigens have been detected and identified. Immunoglobulin
G (IgG) is the predominant class of antibodies in serum,
but IgE has also been detected to a lesser degree. The bile
contains secretory IgA as the principal immunoglobulin.
The parasite antigens manifest IgE-potentiating activity.
Although high antibody titers are achieved in infected
patients, their protective ability is doubtful. Some investigations
have suggested that complement-fixing antibodies may
play a role but Opisthorchis may be able to activate complement
by way of the alternative pathway leading to lymphocyte
killing. Cell-mediated immunity also occurs following
natural infection or immunization with the parasite antigen.
The role of T cells remains to be determined. Primary
infection does not appear to protect against reinfection by
the same parasite. Thus, there appears to be a lack of protective
acquired immunity. The liver flukes survive in the
biliary system that may serve as a type of immunologically
privileged site. These parasites can shed their surface teguments
following injury by immune mechanism, representing
yet another mechanism to evade host defenses.
opportunistic infection
An infection produced by microorganisms that are usually
of relatively low virulence but become more aggressive in
subjects with altered or defective cell-mediated immunity.
Susceptible individuals include individuals with acquired
immune deficiency (AIDS) and severe combined immunodeficiency
(SCID) and organ transplant recipients. Typical
microorganisms producing opportunistic infections include
Pneumocystis carinii, Candida albicans, Mycobacterium
avium intracellulare, Cryptosporidium, Toxoplasma, cytomegalovirus,
and herpesvirus.
opportunistic pathogen
A microorganism that produces disease only in persons
whose immune defense mechanisms are compromised as in
AIDS.
opsonin
A substance that binds to bacteria, erythrocytes, or other
particles to increase their susceptibility to phagocytosis.
A host protein that coats a pathogenic microorganism or
macromolecule to make it bind more readily to phagocyte
receptors, thereby enhancing phagocytosis. Opsonins
include antibodies such as IgG 3, IgG 1, and IgG 2 that are
specific for epitopes on particle surfaces. Following interaction,
the Fc region of the antibody becomes anchored to
Fc receptors on phagocyte surfaces, thereby facilitating
phagocytosis of the particles. In contrast to these so-called
heat-stable antibody opsonins are the heat-labile products of
complement activation such as C3b or C3bi that are linked
to particles by transacylation with the C3 thiolester. C3b
combines with complement receptor 1 and C3bi combines
with complement receptor 3 on phagocytic cells. Besides
immunoglobulins of the mentioned isotypes and complement
proteins, other opsonic complement intermediates
include iC3b and C4b. Opsonins facilitate phagocytosis of
particulate antigens by neutrophils or macrophages. Other
substances that act as opsonins include the basement membrane
constituent known as fibronectin.
Inefficient phagocytosis
Opsonization
Fc receptor
Macrophage
Efficient phagocytosis
Opsonization.
Bacteria
Antibacterial
Ab (opsonin)
opsonization
Facilitation of the phagocytosis of microorganisms or
other particles such as erythrocytes through the coating of
their surfaces with immune or nonimmune opsonins. The
enhanced phagocytosis of a pathogenic microorganism or
macromolecule is attributable to the linkage of molecules that
interact with phagocyte cell surface receptors. Antibodies
such as immunoglobulin G (IgG) molecules and complement
fragments may opsonize extracellular bacteria or other
microorganisms, rendering them susceptible to destruction
by neutrophils and macrophages through phagocytosis.
opsonophagocytosis
Antibodies and/or complement, mainly C3, serve as
opsonins by binding to epitopes on microorganisms and
increasing their susceptibility to phagocytosis by polymorphonuclear
leukocytes, especially neutrophils. Serum
bactericidal activity and phagocytic killing are two principal
mechanisms in host defense against bacteria. Opsonic
antimicrobial antibodies are critical for optimal functioning
of phagocytes in the uptake and containment of bacteria.
oral immunology
Saliva rinses the oral cavity and also contains numerous
molecules such as lysozyme and secretory immunoglobulin
A (IgA) that serve as parts of the mucosal immune system to
help protect the oral cavity. Polymorphonuclear leukocytes
are important in protection of gingival tissues and ultimately
the periodontium. In addition to secretory IgA, the systemic
vascular humoral immune response is significant in oral
immunity. The relative contribution of Th1 and Th2 cells
in an immune response to plaque bacterial pathogens is