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40 Cards in this Set

  • Front
  • Back
Antigen Recognition by B and T cells

How are they different based on receptors?
For adaptive:
BCR = B cell receptor, antigen receptor complex on B lymphocytes

TCR = T cell receptor, antigen receptor complex on T lymphocytes

For innate: PRR = Pattern recognition receptor
Immunoglobulin (Ig) supergene family

How is it named?
Immunoglobin = antibody

All related proteins have Ig domain
For BCR complex, name the 3 parts
1. mIg

2. Ig(alpha)

3. Ig(beta)
Membrane immunoglobulin is domain that recognizes and binds to antigen
2 transmembrane proteins that work together with mIg (antibody) to create signal transduction from the exterior of the B lymphocyte to the interior
Ig(alpha) & Ig(beta)
What are the 3 parts of the TCR complex?

What are their functions?
1. TCR

2. CD3

3. Zeta

CD3 & Zeta work with TCR to create signal transduction for T lymphocyte
Marker for T cells since all T cells have CD3 receptors
Regions of Ig
Fab region
Fc region
C region of Ig
Constant region

Stimulates same function regardless of the antigens that are bound.
V region of Ig
Variable region

Ag recognizing portion of receptors and changes it from clone to clone
Fab region of Ig
Fab = fragment antigen binding region

Each Ab has 2 fab regions
Fc region of Ig
Fc = fragment crystalline region
CDR region of Ig

What is the most variable CDR?
CDR = complementarity determining region

Parts within the V region of both the heavy & light, give specificity for binding antigens

CDR3, located between C and V regions
Ab can be cleaved by what enzymes?
Papain gives 3 fragments: 2 Fab + 1 Fc

Pepsin gives 2 fragments: F(ab')2 + 1 Fc
The isotypes of antibodies

How do they differ?
IgM, IgD, IgG, IgA, IgE

Differ in the composition of the Fc domain
What is the structures of antibodies?
2 H (heavy) chains that associate with 2 L (light) chains
Switching of the H chain of an antibody.

When an IgM can change into an IgG but will produce the same antigen-specific antibody
Class switching
Function of IgM
Membrane surface receptor

Complement activation
Function of IgG

Neutralization (blocks activity of pathogen by changing biological activity of toxic proteins)

Complement activation


Only Ab that can cross the placenta and protects fetus from mom's antibodies through FcRn receptor

Regulation of B cell, stops production of Abs
Function of IgA
Mucosal immunity, neonatal immunity

Found in colostrums & breast milk, gut epithelium
Functions of IgE
Allergic reaction, parasite infection

Works together with eosinophilic and mast cells
Which antibody has the highest concentration in the blood?

Which antibody has the highest concentration in the body tissues?
IgG highest in blood

IgA highest in body tissues
Same Fab, different Fc
Same Ig class from different individuals
Differences of Fab region with each clone.

Unique structure produced by a single clone
Binding strength between the epitope and the antigen-binding site.
How is affinity measured?

Lower the Kd value, the higher the affinity
Naive B cells have medium range of affinity. But once they become activated, their affinity to bind Ag increases.

Occurs only in B cells

Only a somatic mutation so won't be passed down to future B cells
Somatic mutation
Total binding strength based on number of different binding sites and affinities
How is BCR different from TCR
TCR & BCR are both membrane anchored but TCR doesn't secrete.
Describe the TCR structure?
Has 2 chains-heavey and light

Each chain has a V and C region

CDR3 is the most variable region
Where does TCR assembly take place?
In the thymus
The most common type of TCR has what type of chains?
90% of T cells have alpha/beta chains-->MHC restriction (which means they only recognize proteins when presented by MHC molecules)

Recognize peptides (adaptive immunity)
The least common type of TCR has what type of chains?
10% of T cells have TCR as gamma and delta chains-->not MHC restricted

Recognize phospholipids & glycolipids (innate immunity)
Which type of receptor binds Ag with more affinity?
BCR, has a lower Kd value

So TCR needs help from adhesion molecules to bind to epitope
How does TCR get help to bind to epitope?
via CD4 & CD8 receptors

TCR recognizes peptide, CD4 & CD8 recognizes MHC.
Which type of receptor has more diversity and why?
BCR has more diversity because it is made of 3 segments (V-variable, D-diversity, J-joining)

Whereas, TCR has less diversity since it only has V and J segments
For BCR and TCR, only express allel from mom OR dad, not both
Allelic exclusion

Unlike MHC which is codominant
How are the alleles chosen for BCR and TCR?
Random selection

Chose mom OR dad's alleles (not germline change so not passed on)

Ensures one cell, one specificity
Once B cell is committed to one antigen specificity it won't change it's allelic exclusion, even if B cell undergoes a class switch
Clonal selection theory