Immune System I Flashcards
What do accessory cells do?
They process antigen (ingested and paritally degraded foreign substances) and then present processed antigenic fragments on their membranes that can be recognized by lymphocytes
lymphocytes: what role do they play? how so?
specifically recognize and distinguish different antigenic determinants by virtue of their cell surface antigen-specific receptors
receptors are clonally expressed: each lymphocyte expresses only one binding specificity (basis of clonal selection)
lymphocytes then execute the effector mechanisms that characterize acquired immunity
B lymphocytes: what type of immunity do they confer? How do they become specific? What is the difference btw the two types of B cells?
Humoral immunity (antibody-mediated) they express Ig (immunoglobulin) receptors that confer specificity to a given antigen When they encounter the antigen, they divide into memory B cells and effector (plasma) cells. Plasma cells make Ig (aka antibodies) Memory B cells have longer life span
T lymphocytes: what kind of immunity? What controls specificity?
T cells mature in thymus
responsible for cell-mediated immunity
specificity controlled by antigen receptors on the surface (TCRs). TCRs made of polypeptide chains. N-terminal ends make up the antigen combining site.
T cell responds when it encounters an antigenic determinent o n the surface of the accessory cell presented in association with major histocompatibility complexes.
What distinguishes Th cells from Tc cells?
Th: helper cells. Express CD4.
Tc cells: express CD8.
CD4 interacts with class II MHC determinants; CD8 with class I MHC determinants.
What to stimulated Th cells do?
produce cytokines that are nonantigenically-specific small peptides that stimuate functions of T and B cells and other aspects of physiology
What is the difference between the two kinds of helper t-cells?
Th1 cells produce cytokines hthat facilitate cell-mediated immunity;
Th2 cells produce cytokines that facilitate humoral immunity
What is one risk associated with splenectomy?
increased incidence of bacterial sepsis caused by encapsulated bacteria
What are MALTs? What role do they play?
mucosal associated lymphoid tissues. they trap antigens that have gained entry through the epithelial mucous membrane. Can include loosely organized lymphatic tissue or other structures, like tonsils, appendix, and Peyer’s patches.
DiGeorge syndrome
thymus and parathyroids fail to develop owing to failure in the development of the 3rd and 4th pharyngeal pouches. presents with tetany.
Bruton’s agammaglobulinemia
B cell deficiency. X linked recessive defect associated with low levels of immunoglobulins. Recurrent bacterial infections after 6 mo. Defect in tyrosine kinase
SCID
B and T cell deficiency. frequent viral, bacterail, fungal, and protozoal infections. multiple causes
hyper IgM syndrome
Increased IgM levels with low levels of IgG. X linked. Due to a CD40 ligand mutation and defective isotype switching
chronic granulomatous disease
phagocyte deficiency. defect in phagocytosis of neutrophils due to lack of NADPH oxidase activity. Inc. susceptibility to opportunistic infections like S aureus and Aspergillus
Chediak Higashi disease
defect in phagocytosis from microtubular and lysosomal defects. Recurrent pyogenic infections with staph and strep
Job’s syndrome
neutrofils can’t respond to chemotactic stimuli. Lots of IgE. Recurrent staph absesses
Leukocyte adhesion deficiency I
autosomal recessive
bacterial and fungal infections
impaired wound healing defect in B2 integrins and cell adhesion.
Wiskott-Aldrich syndrome
B and T cell deficiency. defect in the ability to mount an IgM response to capsular polysaccharides of bacteria. Recurrent pyogenic infections, eczema, and thrombocytopenia
Selective immunoglobulin deficiency
deficiency in a specific class of immunoglobulins, perhaps due to isotype switching selective IgA deficiency is the most common.
ataxia-telangiectasia
B and T cell deficiency with associated IgA deficiency. Presents with cerebellar probs and spider angiomas
chronic mucocutaneous candidiasis
T cell dysfunction, esp. against candida albicans
What is the definition of an antigen?
Any substance capable of inducing an immune response
What is clonal selection?
the process by which one particular B cell out of a large pop of B cells is selected for clonal expansion and development into a mature plasma cell that secretes a specific antibody
What is a globulin?
a protein that is insoluble in distilled water- requires the presence of dilute salt
what kind of immune response do we see if this is our second exposure to a given antibody?
an anamnestic response
What kinds of antibodies can cross the placenta? Why?
maternal IgG but not IgM or IgA get across the placenta due to a transport processes mediated by a receptor which binds to a potion of the immunoglobulin molecule
alloantigen definition
alloantigen: antigens whos structure is under geneteic control and thus may be present in one person but absent in another due to genetic polymorphism
what is the difference btw the a and b blood groups
A codes for a Gal NAc transferase which transfers N-acetyl galactosamine to H precursor substrate. B codes for a gal transferase that transfers gal to H substance. O has a single base deletion that makes the a protein inactive
Erythroblastosis fetalis
hemolytic disease of the newborn. arises when an Rh neg mom carries an Rh pos fetus to term and generates anti-Rh antibodies. These antibodies can harm subsequent Rh positive fetuses and lead to fetal death. Anto-Rh antibodies are of the IgG type and can cross the placenta. causes hemolytic anemia in the baby.
how do we treat erythroblastosis fetalis?
prophylactic use of a human anti-D (anti-Rho) IgG isotype. causese the immune elimination of antigen before Rho positive cells can provide an antigenic stimulus.
What is an epitope?
the portion of an antigen molecule against which antibody is directed and which serve as determinant of antibody specificity
How do you make a monoclonal antibody?
Primed B cells are fused with HGPRT negative myeloma cells. This is advantageous- they become immortal (from the myeloma cells) and express a specific antibody. Cells are selected for using HAT medium (this medium contains an analog for folic acid. HGPRT negative cells die because they can only make new DNA using the folic acid dependent pathway, and the analog thus leads to cell death).
What is a cross reaction and what role does it play in vaccination?
Cross reaction: partial sharing of reactivity by antigens or antobidies. two antigens which are chemically or structurally related might show immunological cross-reactivity; closer the relationship, the more extensive the cross-reaction. these are called homologous or heterologous antigens (the antigen used to raise the rxn is called the homologous antigen; the related but non-identical antigen is called the heterologous antigen). So, there are two very similar structures, there may be some portions with identical epitopes and you might see some cross-reactivity.
What are two ways to make specific antisera?
- absorption. add some cross reactive protein to a polyclonal mixture. This cross-reactive antigen will precipitate out the non-specific antigen- what is left over will be more specific.
- use monoclonal antibodies
What kind of globulins (alpha, beta, gamma) are immunoglobulins?
gamma
What is the basic immunoglobulin structure?
2 heavy chains and 2 light chains held together in a bilaterally symmetric LHHL arrangement. 4 chains held together by non-covalent interactions. (hydrophobic and hydgen bonding) as well as disulfide bonds
What is the significance of fractioning immunoglobulins with proteases papain and pepsin?
you can produce fragments of antibodies that define functional domains. In this way you can tell which properties of the immunoglobulin depend on the bivalent structures and which ones just depend on monovalent binding
What feature of the immunglobulin defines its class?
the primary structure of the constant portion of its heavy chain
Where does IgG predominate?
in serum and interstitial fluid
What important roles are played by IgM?
first Ig made by neonates
first to be produced in a primary response
has a transmembrane form that is anchored in the lipid bilayer as a monomer where it serves as a receptor for antigen
more efficient than IgG in binding complements and promiting lysis of gram neg bacteria
Where does IgA predominate?
external secretions
Where is IgD found?
sufrace of B cells a s a receptor for antigen or in the serum at low concentrations
Where is IgE found and what is its significance?
not much in serum
very high affinity for receptors of mast cells
important in allergy
What is an isotypic determinant of immunoglobulins?
constant region determinants that distinguish each Ig class and subclass within a species
What is an allotypic determine of immunoglobulins?
subtle amino acid differences encoded in different alleles. detected by comparing the same antibody class among different inbread strains or different members of the same species
What are idotypic determinants of immunoglobulins?
generated by the conformation of the amino acid sequences of the heavy and light chain variable region specific for each antigen. each individual determinant is called an idiotope, and the sume of the individual idiotopes is the idiotype.
What are J chains?
a type of polypeptide chain that occurs only as a subunit in certain polymeric immunoglobulins, esp. serum IgM, serum IgA and secretory IgA.
What is the SC component?
secretory component is another type of polypeptide chaing that occurs only as part of the secretory IgA molecule found in external secretions. part of the molecule involved in exporting sIgA
What is hapten?
low MW substance that isn’t immunogenic alone but becomes immunogenic when coupled or joined covalently to an antigenic carrier protein.
What is a toxoid?
an altered toxin that has been modified to destroy its toxicity but to retain its antigenicity
