Immunology Flashcards
What are the two types of immunity?
- (Innate) Natural
- (Acquired) Adaptive
Innate (Natural) immunity
-Immunity present at birth, first defense, immediately available
ex: ABO isoagglutinin, anti-A and Anti- B
-Ability to recognize and attack pathogens without antigen-specific antibody or cell-mediated immunity
1. Physical barriers: skin, mucous membranes
2. Biochemical Barriers: bactericidal enzymes, saliva, stomach acid
3. Drugs
4. Cellular and humoral: nonspecific response (phagocytosis)
ex: phagocytes, complement, NK cells
Acquired (Adaptive) immunity
-this is learned immunity
-slow (1-2) weeks but long-lived memory
-development of foreign antigen-specific antibody or cell-mediated immunity
ex: B lymphocytes and T lymphocytes
Neutrophils
-also called polymorphonuclear leukocytes, polys, PMSs, granulocytes
-primary effector cells in acute inflammation and innate immunity
-engulf and destroy bacteria and cell debris
-appear within the first 24 to 48 hours
** associate with acute infection **
Macrophages
-called dendritic cells (or macrophages) in tissue
-called monocytes in the blood
-predominant cell in chronic infection
-increases within 48-72 hours in acute infection
-engulf and destroy invaders and cell debris, process it, and present the antigens to T cells
-orchestrate cell-mediated and humoral immunity via direct or cytokine intervention
-also help coordinate the repair process
T cells (T-lymphocytes)
-mostly seen in chronic inflammation
-stimulate and stimulated by macrophages
-produce interleukins, interferuons and other mediators
-recognize and are activated by foreign antigens presented to them by dendritic cells (macrophages)
-activate B cells, assure specificity of the immune response
B cells (B lymphocytes)
-mostly seen in chronic infection
-stimulated by T cells or (inhibited) to divide and produce antibodies (plasma cells) or become memory cells
-they produce antibodies specific for a certain antigen
-effector cells of the humoral response
What are the two types of B cells?
- Plasma cells (produce antibodies)
- Memory cells
What are the 5 classifications/types of immunoglobulins?
- IgG
2.IgA
3.IgM - IgE
5.IgD
What are the three most common and important immunoglobulins in blood banking?
- IgG
- IgM
- IgA
IgG
-most common antibody circulating in blood and tissue, small in size and can only bind a few antigens
-requires a bridge for agglutination and commonly reacts at the AHG phase of testing
-univalent (exists as a single antibody molecule)
-complement fixation = +
-production occurs quickly and in high titer in the secondary immune response
-can cross the placenta and cause hemolytic disease of the fetus and newborn
IgM
-usually, the earliest antibody found during an immune response (primary phase)
-largest immunoglobulin (pentamer), and can bind with several antigens
-can directly agglutinate saline suspended in red cells at room temperature (immediate spin: antibodies of the ABO system) no anti-Ig or anti-C3 present
-complement fixation: ++++
-cannot cross the placenta
-initial IgM response may switch to IgG
-activates the classical pathway of the complement system
IgA
found in serum and body secretions, can cause severe anaphylaxis (allergic) reactions
-often a dimer
Complement system
-part of the immune system that enhances the ability of antibodies and the immunological process
-the most interesting component of complement to blood bankers is C3b
-C3b is left on RBC surfaces after IgM (sometimes IgG) binds to the RBC but the membrane attack complex is not activated
-C3b tells us that antibodies once did bind to the cell
-with some antibodies, the complement cascade will progress all the way to the MAC and lyse the cells intravascularly
What is cellular immunity?
mediated by cells
What is humoral immunity?
-antibodies and complement
NK cells (natural killer)
-Non-T and Non-B cells
-apart of the innate immune system
-first line of defense against various infections: target cell lysis,secret cytokines like IFN-gamma)
-targets tumor cells, cells infected with viruses
-no receptor rearrangement like B or T cells
IgE
-found in tissue and serum
-Antiparasitic functions
-attaches to mast cells and mediates histamine release in allergic hypersensitivity
IgD
-small amounts found in serum, also attached to B cells
What are the properties of antigens that influence immune response?
- Size
- complexity
- charge
- solubility
- composition (proteins, carbohydrates)
Naturally occurring antibodies
-antibodies that result from exposure to environment antigens which cross-react with RBC antigens
ex: ABO isoagglutinin developed against bacterial cell wall antigens
Immune antibodies
-antibodies resulting from exposure to foreign (non-self) RBC antigens
ex: transfusion, pregnancy, and other blood exposures (organ transplant)
What are the methods of foreign antigen exposure?
- transfusion
- pregnancy
- other blood exposure: organ or stem cells
What is the purpose of the antibody screen?
-to check for unexpected antibodies in the patient’s serum which may cause the destruction of transfused donor RBC
* not all unexpected RBC antibodies cause red cell destruction but need to distinguish those from the destructive ones
How are antibodies detected?
hemagglutination
alloantibodies
-directed against non-self antigens as a result from previous exposure to non-self RBCs
-usually detected by indirect antiglobulin test (IAT)
ex: transfusion with allogenic donor RBCs, pregnancy
-less common ex: needling sharing sexual exposure, organ or stem cell transplantation
Allotype
-variations of the isotypes and their subtypes involving the heavy chains and differing among members of the same species
idiotype
-variations between antibody isotypes and subtypes within a single member of a species based on the differences in the variable region
Autoantibodies
-directed against self-antigens
-usually the result of immune dysregulation allowing the production of self-reactive plasma cell clones
-commonly detected by the direct antiglobulin test (DAT)
What are some intramolecular binding forces?
- hydrogen bonding
- Hydrophobic and hydrophilic bonding
What are some antibody properties?
- affinity
- avidity
Affinity
strength of the Fab binding to its epitope or hapten
Avidity
ability of the antibodies in a serum to bind to its antigen
What are some antibody specificity?
- specific reaction
- cross-reaction
- no reaction
specific reaction
-strong fit between lock and key
cross-reaction
similar antigen to the antibody’s true antigen allowing a weaker interaction to take place
Polyclonal
-reacts against more than one epitope on an antigen
1. produced by multiple plasma cell clones
2. inconsistent strength of reaction
3. require animal or human sources which may be variable or unreliable
Monoclonal
-reacts against one specific epitope
1. produced by a single hybridoma plasma cell clone
2. consistent strength of reactions
3. may miss antigens that are missing that specific epitope
What does the proximity of RBCs to each other mean?
- the closer the red cells are next to each other, the easier it is for antibodies to bind them together and agglutinate them
How does centrifugation help?
-physically forces the RBCs together
What is the charge of the red cell surface?
- referred to as the zeta potential and keeps the red cells apart from each other
-one way to decrease this is to use enhancement media potentiators (reagents)
What are reagents that reduce the zeta potential between RBCs
1, LISS
2. PEG
3. Albumin
LISS (non-selective effect)
-contains a reduced concentration of NaCl (0.2%) and results in a reduction in charged ions within the ionic cloud, decreasing zeta potential and facilitating antigen and antibody interactions
-tends to enhance cold antibodies and autoantibodies
PEG (non-selective effect)
-polyethylene glycol
-this enhancement is a water-soluble linear polymer that creates a low ionic environment to increase antibody uptake (concentrates the antibody) by removing water molecules in the test environment to allow a greater probability of collision between antibody and antigen molecules
-tubes with this should not centrifuged or read after incubation at 37
-tubes should go directly from 37 to washing then IAT
-tends to enhance warm antibodies and autoantibodies
What is the antigen-antibody ratio?
-strong lattice formation for agglutination requires the proper ratio of antigen to antibody
- prozone, zone of equivalence, and postzone
Prozone
Antibody excess
Zone of equivalence
-the optimum proportion of antigen and antibody
Postzone
-antigen excess
What pH do antibodies work best at?
-most antibodies work best between a pH of 6.5-7.5
Which antibody works better in a more acidic pH?
-anti-M
-anti-I
What temperature do IgM antibodies work better at?
room temp or lower (colder)
High thermal amplitude
-antibodies that react at a wide temperature range
What temperature do IgG antibodies work better at?
-37 degrees or less (and at the AHG phase of testing using anti-IgG to cross-link and agglutinate)
What is a regent that destroys some antigens (Duffy) and enhances the reactions of others (Rh)
-enzymes
Complete the statement “RBCs coated with IgG…”
-can be agglutinated by the addition of an anti-IgG antibody which spans the Fc portion of two IgG antibodies on two separate RBCs
What are the 2 types of anti-globulin test?
- Direct antiglobulin Test
- Indirect antiglobulin Test
Direct anti-globulin test (DAT)
-antibody already coating the patient’s RBCs in-vivo (in the body)
What are some situations in which you would find a positive DAT?
- autoimmune hemolytic anemias
- Incompatible transfusion reactions
- Hemolytic disease of the newborn
Indirect Anti-globulin test (IAT)
-serum or plasma containing UNKNOWN antibody is added to KNOWN REAGENT RBCs, incubated, washed, added Anti-IgG (AHG). Agglutination occurs in vitro
What does AHG mean
Anti-human globulin
-is an antibody to an antibody
What does the IAT test for?
-test patient serum for unknown or unexpected antibodies against reagent RBC with known antigen
*screens for alloantibodies
The IAT test is the principal method for what other screens/tests?
- antibody screen
- crossmatch test
Carbohydrate based antigens
ex: Lewis and P
-generally IgM class “cold reacting” alloantibodies
-not often clinically significant
Protein based antigens
ex: Rh, Kell
-generally IgG class “warm reacting” alloantibodies
-typically clinically significant
Anamnestic response
-antigen re-exposure (2nd time), rapid response
-typically antibodies are detectable within 3-14 days of re-exposure
Does age and gender have an effect on alloantibody response?
NO
-exception are neonates
What are the factors influencing antibody formations?
- exposure frequency
- Immune competency of the host
- Antigen immunogenicity (provoke immune response)
*Rh system D(Rho) has 50% immunogenicity
Enzyme treatment
-papain/ ficin enhances antibody avidity by degrading RBC sialic acid residues
-selective enhancement of some antigens (ABO, Rh, Kidd, Lewis)
-selective destruction of others (FY, MNSs, Xga, JMH, and others)
Automated methods
-reflect an interaction between patient serum and reagent cells in a gel or solid phase medium
-like manual methods the endpoint is agglutination
-pros: increased sensitivity of detection; automated testing; less subjectivity
-Cons: elimination of immediate spin testing, increased junk reactions
Automated antibody detection: Gel method
-specimens are added to a polyamide gel column for observation and agglutination
-gel increases ag-ab interactions
-specimens are centrifuged and results are read
-gel cards can be saved for review
-agglutination is a positive rxn
-more likely to give false positives
Automated antibody detection: solid phase
-microplate approach wherein antigen-coated wells are mixed with patient specimen
-specimens are centrifuged and results are read
strong positive = well is coated (no agglutination)
negative = agglutination (solid dot)
-more likely to give false positives
Reaction phase and clinical significance
-most alloantibodies are detected at immediate spin by tube and are generally deemed cold-reacting and clinically insignificant
-these are IgM class and activity eliminated with incubation
-can be important in certain settings (cardiothoracic surgery)
-cold reactive antibodies are not usually detected by gel/solid phase
-alloantibodies detected at 37/AHG should be considered clinically significant (IgG)
Classical pathway
antigen-antibody complex
-C1 C4 and C2 –> C3 convertase –> C3b
Lectin pathway
-serum lectin binds to mannose residues on pathogens
MASP, C4, C2 –> C3 convertaste –> C3b
Alternative pathway
pathogen cell membrane
C3b, factor B, factor D –> C3 convertaste –> C3b
