Antigens and The Major Histocompatibility Complex Flashcards
macromolecules capable of triggering an adaptive immune response by inducing the formation of antibodies or sensitized T cells in an immunocompetent host
immunogens
a substance that reacts with antibody or sensitized T cells but may not be able to evoke an immune response
antigen
T/F
all immunogens are antigens but not all antigens are immunogens
true
Older individuals are more likely to have a decreased response to antigenic stimulation, neonates do not fully respond to immunogens, because their immune systems are not completely developed
age
Individuals who are malnourished, fatigued, or stressed are less likely to mount a successful immune response
overall health
A threshold dose, allows the innate immune response to take care of small amounts of pathogens and leave the adaptive response for pathogens that are present in large numbers
dose
Include intravenous (into a vein), intradermal (into the skin), subcutaneous (beneath the skin), and oral administration
route of inoculation
Linked to the MHC and to the receptors generated during T and B lymphocyte development
genetic capacity
molecular weight of at least 10,000 to be recognized by the immune system, and the best immunogens typically have a molecular weight of over 100,000 daltons
macromolecular size
______ is that the greater the molecular weight, the more potent the molecule is as an immunogen
the rule of thumb
proteins and polysaccharides are the best immunogens (amino acids)
chemical composition and molecular complexity
_______ recognize structures that project from the external surfaces of macromolecules
B cells
_____ have epitopes that also stimulate T cells, which is essential to generating T-cell help in antibody production
proteins
_______ are somewhat less immunogenic than protein
carbohydrates
Carbohydrates are somewhat less immunogenic
than protein:
glycolipids or glycoproteins
the A, B, and H blood group antigens are _______
glycolipids
the Rh and Lewis antigens are _______
glycoproteins
_______ and _______ are not immunogenic by themselves, although a response can be generated when they are attached to a suitable carrier molecule (DNA protein complex)
pure nucleic acids and lipids
being able to distinguish between self and non-self, and those substances recognized as non-self are immunogenic
foreignness
involves enzymatic digestion to create small peptides or pieces that can be complexed to MHC molecules to present to responsive lymphocytes
The ability to be processed and presented with MHC molecules
Determinant site
epitope
Molecular shapes or configurations that are recognized by B or T cells, may be repeating copies, or they may have differing specificities
epitope
Linear or conformational
epitope
surface antibody on B cells may react with both linear and conformational epitopes present on the surface of an immunogen
Epitope recognition by B cells
T cells recognize an epitope only as a part of a complex formed with MHC proteins on the surface of an antigen-presenting cell
Epitope recognition by T cells
Non-immunogenic materials that, when combined with a carrier, create new antigenic determinants
haptens
May be complexed artificially with carrier molecules in a laboratory setting, or this may occur naturally within a host and set off an immune response
haptens
Antigens that belong to the host
autoantigens
These do not evoke an immune response under normal circumstances
autoantigens
From other members of the host’s species
alloantigens
Capable of eliciting an immune response
alloantigens
They are important to consider in tissue transplantation and in blood transfusions
alloantigens
From other species, such as other animals, plants, or microorganisms
heteroantigens
Heteroantigens that exist in unrelated plants or animals but are either identical or closely related in structure so that antibody to one will cross-react with an antigen of the other
heterophile antigens
A substance administered with an immunogen that
increases the immune response; acts by producing a
local inflammatory response that attracts a large number of immune system cells to the injection site
adjuvants
______ are the only ones approved for clinical use in the United States, and these are used to complex with the immunogen to increase its size and to prevent a rapid escape from the tissues
aluminum salts
aluminum salts must be injected into the ____ to work
muscle
_____ is an example of using this type of adjuvant
hepatitis b vaccination
______ are thought to enhance the immune
response by prolonging the existence of immunogen in the area, increasing the effective size of the immunogen, and increasing the number of macrophages involved in antigen processing
adjuvants
Formerly referred to as human leukocyte antigen (HLA)-Dausset
Major Histocompatibility Complex Molecules
They determine whether transplanted tissue is histocompatible and thus accepted or recognized as foreign and rejected
Major Histocompatibility Complex Molecules
Main function is to bring antigen to the cell surface for recognition by T cells, because T-cell activation will occur only when antigen is combined with MHC molecules
major histocompatibility complex molecules
They are relevant, because they may be involved in transfusion reactions, graft rejection, and autoimmune diseases
major histocompatibility complex molecules
Genes controlling expression of these molecules
are actually a system of genes known as the _______
major histocompatibility complex (MHC)
Genes coding for the MHC molecules in humans are
found on the ______ and are divided into three categories or classes
short arm of chromosome 6
______ are coded for at three different locations or loci, termed A, B, and C
class I molecules
_____ are situated in the D region, and there are several different loci known as DR, DQ, and DP
class II genes
There is a gene that codes for the alpha chain and one or more genes that code for the beta chain
class II genes
______ coded between the class I and class II regions on chromosome, codes for complement proteins and cytokines such as tumor necrosis factor
class III
Expressed on all nucleated cells
class I
Highest on lymphocytes and low or undetected on liver hepatocytes, neural cells, muscle cells, and sperm
class I
Class I:
The alpha chain has a molecular weight of ______
45,000
A lighter chain associated with it, called a ______, has a molecular weight of ______ (alpha chain domains – a1, a2, a3)
beta2-microglobulin
12,000
reacts with CD8 on cytotoxic T cells
a3
Found primarily on antigen-presenting cells, which
include B lymphocytes, monocytes, macrophages, and dendritic cells
class II
___ is expressed at the highest level, as it accounts for
about one-half of all the class II molecules on a particular cell
DR
_____ is the most highly polymorphic, as 18 different alleles are known at this time
DR gene
Both the chain, with a molecular weight of 33,000, and the chain, with a molecular weight of 27,000, are anchored to the cell membrane
class II
To bind peptides within cells and transport them to the plasma membrane, where T cells can recognize them in the phenomenon known as antigen presentation
Role of MHC Class I and II
Mainly present peptides that have been synthesized within the cell to CD8 (cytotoxic) T cells
class I
The watchdogs of viral, tumor, and certain parasitic antigens that are synthesized within the cell
class I
Display of hundreds of class I molecules complexed to antigen allows CD8+T cells to continuously check cell surfaces for the presence of non-self-antigens
class I
If it recognizes an antigen as being foreign, the
CD8+T cell produces _____ that causes lysis of the entire cell
cytokines
Present antigen to CD4 (helper) T cells
class II
Mainly bind exogenous proteins – those taken into the cell from the outside and degraded
class II
Stimulate CD4 T cells in the case of bacterial infections or the presence of other material that is endocytosed by the cell
class II
On the cell surface, ______ are responsible for forming a trimolecular complex that occurs between antigen, class II molecule, and an appropriate T-cell receptor
class II molecules
If binding occurs with a T-cell receptor on a CD4+T cell, the T helper cell recruits and triggers a B-cell response resulting in _____
antibody formation
