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invasin 418 Ir genes
of major histocompatibility complex (MHC) class II
molecules to cell surfaces. It directs the MHC class II
molecules to endosomes where Ii is degraded, permitting
MHC class II molecules to bind peptides in the endosomes.
The Ii chain stabilizes the class II molecule before
it acquires an antigenic peptide.
invasin
A membrane protein derived from Yersina pseudotuberculosis
that binds to α 4β1 integrins and has the capacity to
induce T cell costimulatory signals.
invasive pathogen
A pathogenic microorganism that successfully gains access
to the body even though defense mechanisms are intact.
invasive tumor
A neoplasm capable of accessing and obliterating healthy
architectures of adjacent organs.
inversional joining
An event that takes place during V(D)J recombination when
the two gene segments to be united are in the opposite
transcriptional orientation.
invertebrate immunity
Invertebrates have various mechanisms to recognize
and respond to nonself substances even though they
lack lymphoid immune systems. They possess both
cellular and humoral components that mediate immunelike
responses. Invertebrate internal defense responses
include phagocytosis, encapsulation, and nodule formation.
The molecular recognition and effector mechanisms
among species are diverse. Some of the factors
involved include α 2 macroglobulins, C-reactive proteins,
antibacterial peptides, serine proteinases and proteinase
inhibitors, C-type lectins and complement-related
factors, glucan-binding proteins, and some antibacterial
peptides. Alloaggressive responses have been observed
in noncolonial invertebrates. Invertebrates form certain
members of the immunoglobulin superfamily such as
adhesion molecules and receptors for tyrosine kinases.
Within the immunoglobulin superfamily, only hemolin,
a protein isolated from lepidopterans, is induced following
bacterial challenge. Hemolin has four immunoglobulin-like
domains whose primary structures more closely
resemble cell adhesion molecules than immunoglobulins.
With respect to invertebrate effector molecules,
antibacterial peptides are classified into several families
that include lysozymes, cecropins, sapecins or insect
defensins, and attacin-like and proline-rich antibacterial
peptides. Invertebrates have cascades of endogenous serine
proteinases that are important in defense. Cytokinelike
activity, possibly mediated by factors equivalent to
IL1 and IL6, has been recognized. Receptors have also
been identified on phagocytic cells. Thus, invertebrate
cytokine-like factors may play a role in the regulation
of nonspecific responses to tissue injury and infection.
Opioid peptides, opiate alkaloids, and other neuropeptides
may modulate chemotaxis and cell adhesion.
invertebrates
Animals without backbones.
inverted repeat
Complementary sequence segments on a single strand of
DNA. A palindrome when the halves of an inverted repeat
are placed side by side.
in vitro (“in glass”)
Investigations with living cells or cellular components performed
outside the bodies of intact organisms. The investigations
are performed in tissue culture plates or test tubes.
in vivo (“in life”)
Investigations performed in intact living organisms.
ion exchange chromatography
A method that permits the separation of proteins in a
solution, taking advantage of their net charge differences.
It involves the electrostatic binding of proteins onto a
charged resin suspended in a buffer and packed into a column.
Because serum protein charges vary, binding to or
elution from the column is possible by gradually increasing
or decreasing the salt concentration (with or without
changes in pH). This affects the types of proteins binding
to the resin. With buffers of low molarity and pH >6.5,
the immunoglobulin G (IgG) in solution is not adsorbed
on the column and passes through with the first buffer
volume.
ionic bonds
Electrostatic bonds.
– +
–NH 3
OOC–
Electrostatic forces.
ionic (or Coulombic) forces
Forces resulting from the interactions of oppositely charged
ionic groups on antigen and antibody molecules. Based on
Coulomb’s equation:
F = Q + Q -
εr 2
where ε is the dielectric constant of the medium, Q + and Q -
are the positive and negative charges in electrostatic units,
respectively, and r is the distance between the centers of the
charged sites, the Coulombic force of attraction is inversely
proportional to the square of the distances between antigen
and antibody.
IP-10
Interferon γ (IFN-γ)-inducible protein 10. A chemokine of the
α (CXC) family. IP-10 is a gene product following stimulation
of cells within IFN-γ. It does not posses the ELR motif
that determines the biological significance of a particular
α chemokine. IP-10 has an angiostatic potential, which is
opposite to the angiogenic effect of other ELR-containing
α chemokines. This potential renders IP-10 a unique α
chemokine family member. Tissue sources include endothelial
cells, monocytes, fibroblasts, and keratinocytes. High levels of
IP-10 transcripts are present in lymphoid organs. Monocytes,
progenitor cells, and natural killer cells serve as targets.
IPEX
Abbreviation for immunodysregulation, polyendocrinopathy,
enteropathy X-linked (IPEX) syndrome.
Ir genes
Immune response (Ir) genes. Major histocompatibility complex
(MHC) class II genes that control immune responses
are found in the Ir region. These genes govern the ability
of an animal to respond immunologically to any particular
antigen. Ir genes encode polymorphic MHC molecules
that bind peptides needed for T cell activation and are