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CMB2004 > Lecture 1 > Flashcards

Lecture 1 Flashcards

1
Q

What are the sources of infection?

A

Pathogens

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2
Q

What are pathogens?

A 
Organisms that cause disease
• Bacteria
• Viruses
• Fungi
• Parasites (Worms, Protozoa)
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3
Q

What must the immune system be able to do for an effective immune response?

A

Be able to recognise & respond to any invading organism

Not over react to benign or self

Be able to direct different effector mechanisms against different pathogens

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4
Q

What is the difference between innate & adaptive immunity?

A

Innate is activated very quickly

Adaptive takes over if innate doesn’t completely control the pathogen

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5
Q

What is specific/adaptive immunity

A

Induced by exposure to a particular infection

Shows a high degree of specificity

Exhibits memory

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6
Q

Features of specific immunity

A

Clonally distributed receptors

Large repertoire

Response takes time to develop

Memory cells produced

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7
Q

Clonal selection

A
  1. Removal of potentially self-reactive immature lymphocytes by clonal deletion
  2. Pool of mature naïve lymphocytes
  3. Proliferation & differentiation of activated specific lymphocytes to form a clone of effector cells

Followed by clonal expansion

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8
Q

What are the 2 lymphocyte receptors for antigens?

A

B lymphocytes

T lymphocytes

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9
Q

B lymphocytes

A

BCR expressed by B cells

Membrane anchored protein on the surface of B cell

Binds free antigen

Is subsequently secreted with B cell is activated = an antibody

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10
Q

T lymphocytes

A

TCR expressed by T cells

Membrane form only - stays on the surface where it functions

Recognises a peptide fragment of antigen bound to MHC expressed by APCs

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11
Q

What do antibodies do?

A

Activation of complement

Activation of effector cells

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12
Q

What are antibodies made of

A

Formed of 4 polypeptides
• 2 heavy chains & 2 light chains

Formed by domains - variable & constant

Held together by covalent & non-covalent bonds

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13
Q

Pathogens that may infect mammals can include fungi, bacteria, viruses as well as large, multi-cellular organisms such as …

A

parasites - worms, protozoa

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14
Q

The first phase of an immune response is known as the innate response with the second phase called the …

A

Adaptive immunity

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15
Q

The acquired phase is specific and relies on the detection of infectious agents using …

A

antibodies/cytokines specific for that pathogen

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16
Q

Why is the secondary immune response more effective than the primary response?

A

The memory cells recognise the pathogen, and the antibodies can respond much faster.

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17
Q

Antibody structure:

A
  • immunoglobulin
  • basic 4-chain structure
  • 2 identical heavy chains & 2 identical light chains, held together by covalent and non-covalent bonds
  • 2 types of L chain (λ & κ)
  • each chain has a variable (V) and a constant (C) region
  • antigen-binding sites (variable region) consist of VH and VL
  • different CH regions interact with complement and the Fc region binds to different FcRs expressed by effector cells (macrophages, neutrophils, NK cells)
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18
Q

What do the variable & constant regions do?

A

Variable regions form the antigen-binding sites - specific for a given Ab

Constant regions are responsible for antibody structure & interacting with other molecules

19
Q

What are the 2 types of light chain?

A

Lambda and Kappa

20
Q

5 antibody classes - what are they?

A

IgM, D, A, G and E

Isotype is determined by the heavy chain (C region)

Isotypes differ in their structure and functions

21
Q

Antibody domains

A

Analysis of amino acid sequences of H and L chains reveals homology regions (domains)
each domain ~ 110 amino acids
each domain comprises two b sheets,
linked by a disulphide bridge (S-S, C)
domains are paired –> folded units within the protein

22
Q

Immunoglobulin-like domains

A

present in a range of other proteins:
Immunoglobulin superfamily
includes:
TCR, MHC class I and II, various other molecules
(e.g. CD4, CD8, CD80, CD86, CTLA-4, KIR, IL-6R)

23
Q

Antibody – antigen interaction:

A
  • variable region (heavy and light chains)
  • V regions are specific for a given Ab
  • concentrated region of variability
  • hypervariable regions (3 in VH & VL)
  • HV1-3
  • 6 hypervariable loops-> Ag binding site
  • complementary-determining regions (CDR1-3)
  • both heavy and light chains contribute
  • Ag binds to aa in CDRs
  • size/shape of Ag affects binding
24
Q

Antigen recognition:

A
  1. epitopes recognised by antibodies may be continuous or conformational (discontinuous)
  2. Ag can be almost any molecule (protein, polysaccharide even nucleic acids), along with non-biological molecules e.g. chemicals, metals
  3. antibody and Ag form non-covalent interactions
  4. Ag sequence may be manipulated in vaccine design
  5. Ag may be folded
  6. CDRs present in antibody V regions determine the specificity and the affinity of an antibody for Ag
25
Q

What are the 2 chains of an antibody called?

A

Heavy and light chains.

26
Q

Which part of an antibody interacts with the epitope of an antigen?

A

The variable domains of the heavy and light chains (VH and VL)

27
Q

Define the Fab and the Fc regions of an antibody?

A

The Fc region is constant. The Fab region binds to antigens and consist of VH and VL

28
Q

The antigen binding site of an antibody is made up of …

A

VH and VL

29
Q

The Lamda and Kappa chains form the L chain of an antibody?

A

Light

30
Q

How many hypervariable regions are involved with antigen binding in a single antibody molecule?

A

3 in VH and 3 in VL – 12 in total

31
Q

Antibodies only recognise peptide antigens?

A

False, antigens can be almost any molecule (protein, polysaccharide, nucleic acids, chemicals, metals)

32
Q

Lymphocyte receptors for antigen:

A

• TCR expressed by T lymphocytes:

membrane form only

recognizes peptide fragment of antigen bound to MHC expressed by APC

33
Q

What does a TCR do?

A
  • unlike antibody, it doesn’t bind free antigen
  • binds/recognizes processed antigen (peptides)
  • “presented” in the cleft/binding “groove” of MHC class I or class II molecules
34
Q

TCR:

A
  • membrane bound receptor (and unlike BCR is not secreted)
  • smaller than BCR/antibody (only 4 Ig-like domains)
  • recognizes short peptide fragments (of Ags) bound to MHC molecules on other cells (i.e. not free/ “native” antigens)
  • heterodimer of a and b chain (sometimes g and d)
  • each chain has a V and a C region
  • domains (x4) are Ig-like
  • V domains interact with antigen = peptide bound to MHC molecule
  • each chain contributes 3 CDRs to Ag binding
35
Q

Major histocompatibility complex (MHC) molecules

A 
chromosome 6, 7 x106 bp
MHC class I (expressed by nearly all cell types in body)
MHC class II (expression restricted to a specialized group of immune cells)
36
Q

MHC class I and II

A
  • related, but different structures
  • different expression patterns
  • present peptides from different sources
  • many alleles (polymorphic)
  • first identified due to role in transplant rejection
37
Q

MHC class I

A

• expressed on all nucleated cells
• heterodimer: a chain (43 kD)
b2- microglobulin (12 kD)
• in humans three different MHC class I molecules: HLA-A, HLA-B and HLA-C
• HLA-A, B and C molecules are encoded by separate a chain genes. A single (non-MHC located) gene encodes b2-microglobulin which associates with HLA-A, HLA-B and HLA-C
• a1 and a2 domains fold to form b-sheet structure known as peptide binding site (“groove, cleft”)
• DNA encoding encoding a1 and a2 domains is very polymorphic (many alleles differ here)
• a3 domain/b2-microglobulin fold into “Ig-like” domains

38
Q

MHC class II

A

• expression limited to APC (and cytokine-activated cells)
• heterodimers, a and b chains similar size (34 and 29 kD) and both transmembrane
In humans three different MHC class II molecules: HLA-DP, HLA-DQ and HLA-DR
• a and b chains encoded by separate genes encoded within MHC
• both a2 and b2 domains are Ig-like
• similar structure to MHC class I molecules
• polymorphic a1 and b1 domains form peptide-binding site
• more open than “groove” seen in MHC class I molecules, and binds longer peptides)

39
Q

TCR, CD8 and CD4

A 
The TCR expressed by a T cell that co-expresses CD8  can bind MHC class I molecules (that expressed on most cells)
The TCR expressed on a T cell that co-expresses CD4 will bind MHC class II molecules expressed on APC
40
Q

Summary Antibody

A

H2L2, expressed on B cells, also secreted
Binds free antigens
Highly variable, clonally distributed

41
Q

Summary TCR

A

alpha beta on T cells
Binds peptide-MHC complex: dual specificity
Highly variable, clonally distributed

42
Q

Summary MHC class I

A

alpha chain plus beta2-microglobulin, expressed on all nucleated cells
Binds peptide 8-10 amino acids to present to TCR
Highly polymorphic, limited variation in one individual

43
Q

Summary MHC class II

A

alpha beta chain heterodimers, expressed on APC
Binds peptide 13+ amino acids to present to TCR
Highly polymorphic, limited variation in one individual

CMB2004 (4 decks)

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