MAA - immuno Flashcards

1
Q

Nom du mécanisme pour créer les récepteurs des LB et des LT?

A

VDJ rearrangement

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2
Q

Nomme les 4 caractéristiques du VDJ rearrangement.

A
  • Recombinaison aléatoire des gènes V D et J
  • Plusieurs gènes V D et J
  • Processus “error prone”
  • Réassortiment aléatoire des deux chaines
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3
Q

De quoi est composé le récepteur B?

A
  • Light chain
  • Heavy chain
  • Région Fab
  • Région Fc
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4
Q

Combien de Fab sur un récepteur B?

A

2

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5
Q

Décrit Fc.

A

Région constante qui détermine la sorte d’Ig et si il s’agit d’un récepteur ou d’un anticorps

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6
Q

Décrit la composition d’un récepteur T.

A
  • Chaine a
  • Chaine b
  • 1 seul site à antigène
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7
Q

Nom de la région en contact avec l’antigène?

A

Hypervariable region

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8
Q

À quoi sert le VDJ rearrangement?

A

À créer des récepteurs uniques

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9
Q

Décrit la première étape du réarrangement VDJ.

A
  • Héritage de multiples gènes V D J
  • Ordre: V → D → J → C
  • Réarrangement random de l’ordre des gènes
  • ex: V2-D2-J1 vs V2-D3-J1
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10
Q

Décrit la manière de réarranger les exons VDJ.

A
  1. ADN fait des loops pour attacherdeux séquences
  2. RAAG1 et RAAG2 vont couper l’ADN aux séquences de recombinaison
  3. Artemis va réparer l’ADN en laissant partir une partie extrachromosomale
  4. TdT va rajouter des séquences d’acide nucléique à la fin
  5. Collage final de tout les bouts via la ligase
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11
Q

Nomme les séquences des signaux de recombination.

A
  • heptamer - 5’-CACAGTG-3’
  • 12 nucleotides, corresponding to 1 turn of the DNA double helix, or exactly 23 nucleotides, corresponding to 2 turns of the DNA
  • nonamer sequence - 5’-ACAAAAACC-3’
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12
Q

Qu’est-ce qui se passe entre la création de la chaine lourde et de la chaine légère?

A
  • Test de la chaine lourde
  • LB → VprobB
  • LT → pre-T alpha
  • Si le test fonctionne → signaux de prolifération
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13
Q

Décrit la formation de la chaine légère.

A
  • Réassortiment aléatoire
  • VDJ arrangement
  • Test d’auto-réaction → si ça ne réagit pas aux anticorps du soi = prolifération
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14
Q

Est-ce que les chaines légères ont des régions D?

A

Non

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15
Q

Qu’est-ce qui se passe si la chaine légère est réactive au soi?

A

Elle se réarrange jusqu’au manque de matériel génétique = mort

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16
Q

Est-ce que les deux sites des récepteurs des LB sont identiques?

A

Oui → mêmes chaines lourdes et légères

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17
Q

Quelle chaine des LB change durant la maturation?

A

Lourde → code pour les isotypes d’immunoglobulines

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18
Q

Nomme les types d’immunoglobulines.

A

IgM, IgD, IgG, IgA, and IgE

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19
Q

Qu’est-ce que la valence d’un anticorps?

A

Le nb d’antigènes qui se collent à lui
ou
Le nb de région Fab

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20
Q

Décrit les IgM.

A
  • premier anticorps
  • 4% des Ig
  • Monomère ou pentamère
  • Pas besoin de LT
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21
Q

Par quoi est lié le pentamère d’IgM?

A

Lien covalent
Chaine J

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22
Q

Rôles de l’IgM?

A

Active +++ complément
Opsonine

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23
Q

Décrit l’IgG.

A
  • 75% des Ig
  • valence de 2
  • 4 sous classes
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24
Q

Rôle de l’IgG?

A
  • Opsonine
  • Activation du complément
  • Aide les cellules NK à tuer des cellules
  • Traverse le plancenta
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25
Q

Décrit le rôle des IgG en ADCC.

A
  • Bind aux antigènes des virus
  • Se colle au récepteur CD 16 des NK
  • NK sécrète des granzymes
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26
Q

Décrit les IgA.

A
  • 20%
  • Monomère avec valence de 2
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27
Q

Rôle de l’IgA?

A

Opsonine
Antigène des muqueuses

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28
Q

Décrit le rôle des IgA dans les muqueuses.

A
  1. Dimères d’IgA se lient au POLY-Ig receptor
  2. Transport dans la cellule dans une vésicule avec une partie du récepteur
  3. Protection de l’IgA dans la muqueuse
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29
Q

Nomme les deux formes d’IgA.

A

IgA1
IgA2

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30
Q

Que font les IgA dans les muqueuses?

A

Neutralisent et se lient aux pathogènes
Permet la bonne fonction des cils

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31
Q

Méthode de transmission des IgA aux bébés?

A

Lait maternel

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32
Q

Décrit les IgE.

A
  • Allergie et parasite
  • 0,004%
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33
Q

Décrit la fonction de IgE.

A
  • Bind à Fc epsilon pour aider les granulocytes à “vomir” leurs granules
  • Allergies :(
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34
Q

Décrit les IgD?

A
  • 1%
  • Monomère
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35
Q

Rôle de IgD?

A

Signal de départ de la moelle osseuse pour les LB

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36
Q

Décrit en bref l’activation des LB

A
  1. Présentation de l’antigène sur un BCR
  2. Internalisation de l’antigène par le LB
  3. Présentation sur un MHC 2
  4. Présentation au CD4
  5. Liaison entre les CD40 L et R
  6. Activation de AID
  7. Production d’antigènes de différentes classes
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37
Q

À quoi sert AID?

A

This enzyme is only found in B cells and allows them to make cuts in the DNA, causing the B cell to class-switch from IgM to IgG, IgA, or IgE.

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38
Q

À quoi sert le CD4 dans la production de IgX par le LB?

A

Il lui envoie des cytokines pour lui indiquer quel Ig faire

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39
Q

Dans quelles cellules se fait la permutation isotypique?

A

LB

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40
Q

Pourquoi AID permet la permutation isotypique?

A

AID can only bind to single-stranded DNA, so it’s really only able to target genes that are being actively transcribed during the rapid proliferation phase that occurs following B cell activation

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41
Q

Comment fonctionne AID?

A

turning a cytidine into a uridine in the DNA

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42
Q

Décrit la permutation isotypique.

A
  1. Cystidine devient uridine
  2. U ne peut plus s’associer à G
  3. Processus de mismatch repair ou de base excision
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43
Q

Décrit le processus de mismatch repair.

A
  1. MSH2 et MSH6 recrute des nucléases pour enlever U et un bout d’ADN autour
  2. ADN polymérase vient remplacer les nucléotides et fait des fautes!
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44
Q

Décrit le processus de base exciion.

A
  1. ADN glycosylase enlève la base uracile de l’uridine
  2. Remplace donc U par un nucléotide random par l’ADN polymérase
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45
Q

Comment se fait la formation de Ig de + en plus spécifique par les LB?

A
  • If a B cell’s affinity is so low that it doesn’t respond to the antigen anymore, then the B cell will simply stop getting activated and will die out over time.
  • Meanwhile other cells will get a stronger and stronger affinity over the generations and this is what leads to affinity maturation.
  • It’s really like natural selection
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46
Q

Nomme les deux types de LT.

A

CD4
CD8

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47
Q

Qu’est-ce que l’immunité cellulaire?

A

refers to the part of the immune response that’s based on cellular interactions

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48
Q

Décrit l’activation d’un LT.

A
  1. Présentation d’un antigène sur un MHC qui se lie au récepteur TCR
  2. Co-stimulation via la liaison du CD28 avec B7
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49
Q

Nomme les 3 composantes du récepteur IL2 du LT mature.

A

a
b
gamma

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50
Q

Comment se fait l’expansion clonale?

A

Le LT mature relâche des IL2 qui le stimule

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51
Q

Gènes et types de LT créé par:
- IL12
- Interféron gamma
- Interféron béta

A

Stat 1, stat 4 et Tbet
TH1

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52
Q

Fonctions de TH1?

A
  • Interféron g → boost la production de ROS, NO et protéases des macrophages
  • CD40 ligan → stimule les macrophages
  • IL2 → prolifération des NK, CD8 et LB
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53
Q

Gènes et types de LT créé par:
- IL4
- IL5
- IL10

A

Stat 6 et Gata 3
TH2

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54
Q

Fonctions de TH2?

A
  • IL4, IL5, IL10, IL13 → stimule IgE
  • Stimule la dégranulation des basophiles et mast cells
  • IL5 → recrute des éosinophile
  • IL13 → augmente la sécrétion de mucus et le péristaltisme intestinal
  • IL4-IL5 → stimule le TH2
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55
Q

Gènes et types de LT créé par:
- IL1
- IL6
- IL 23
- TGF béta

A
  • RORgamma-t et Stat 3
  • TH17
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56
Q

Fonctions de TH17?

A

IL17 → recrute neutrophiles

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57
Q

Gènes et types de LT créé par:
- IL6
- IL 21
- IL27

A
  • Bcl-6 et cMAF
  • Tfh
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58
Q

Rôle des Tfh?

A
  • IL21 et interféron gamma → génère des LB mémoire
  • CD4 → expriment des récepteurs à cytokines sur les LB
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59
Q

Par quel phénomène sont activés les LT?

A

Cross presentation

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60
Q

Comment le CD8 fonctionne-t-il?

A
  1. Bind à un MHC1 d’une cellule
  2. Utilise LFA1 pour se lier à ICAM
  3. Câlin de la mort si bonne affinité
  4. Activation du SMAC
  5. Relargage de perforines et de granzymes
  6. Mort de la cellule cible
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61
Q

Que contient SMAC?

A
  • cSMAC → TCR
  • pSMAC → LFA1
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62
Q

Comment les cellules NK font-elles pour tuer?

A
  • Récepteurs activateurs → NKG2d
  • Récepteurs inhibiteurs → KIR ou NKG2a
  • Évalue la quantité et la qualité des récepteurs MSH1 sur les cellules
  • Si plus de signaux de tuer que de laissez passer → on tue la cellule
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63
Q

Comment est-ce que NK tue la cellule?
ADCC

A

Le récepteurs CD16 va se lier à un IgG sur la cellule à tuer

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64
Q

Que sécrète NK et à quoi ça sert?

A

Interféron gamma
Active macrophages

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65
Q

À quoi servent kes CD4?

A
  • Différentiation des LB
  • Switch classe
  • Production d’anticorps
  • Recrute phagocytes
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66
Q

Comment est créé un Treg?

A

when a T cell responds a little too strongly to a self-antigen but not strong enough to be killed, it’s instructed to upregulate the transcription factor FOXP3, which guides its development into regulatory cells

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67
Q

Qu’exprime un Treg?

A

CTLA4 → inhibe B7
IL2 et adénosine +++

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68
Q

Décrit l’anergie clonale.

A
  • Quand un LT ne reçoit pas de costimulation
  • Auto-antigènes ne font pas de B7
  • TCR et CTLA4 ne fonctionnent plus
  • Inactivation du LT
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69
Q

Décrit la délétion périphérique.

A
  • Quand les LT reconnaissent un antigène du soi
  • Produisent moins IL2 et augmentent le Fas → apoptose
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70
Q

Décrit le développement de la tolérance périphériqe des LB.

A
  • Un LB qui reconnait le soi ne sera jamais activé par un LT
  • Pas de différenciation ni de sécrétion d’anticorps
  • Mort
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71
Q

Décrit la réaction d’hypersensibilité de type 1.

A

Régulée par IgE

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72
Q

Nomme les étapes de l’hypersensibilité de type 1.

A
  1. Exposition #1
  2. Antigène est mangé par macrophage qui le présente dans les ganglions
  3. Activation des LT → TH2
  4. Médiation des LB → IgE qui vont se coller aux mastocytes
  5. Recrutement d’éosinophiles
  6. Exposition #2
  7. Activation et dégranulation des mastocytes
  8. Histamine → vasodilatation, bronchospasme, urticaire
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73
Q

Décrit la late phase reaction dans la réaction d’hypersensibilité de type 2.

A
  • 8-12h post exposition
  • IL4-5-10 et leukotriènes
  • +++ de neutrophiles, mastocytes, éosinophiles
  • Contraction muscle lisse
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74
Q

Tx de l’hypersensibilité de type 1?

A

Antihistaminique
Cortico
Épinéphrine

75
Q

Par quoi est médié l’hypersensibilité de type 2?

A

Anticorps
Tissus spécifique

76
Q

Décrit les étapes de l’hypersensibilité de type 2.

A
  1. LB crée des IgG ou IgM qui s’attachent à la pénicilline
  2. La pénicilline s’attache à un GR
  3. Activation du complément
  4. Destruction du GR
77
Q

Qu’est-ce qui tue la cellule dans l’hypersensibilité de type 2?

A
  • C3a-C4a-C5a → chimiotaxique pour les neutrophiles
  • MAC → lyse de la cellule
  • C3b → opsonisation
78
Q

Nomme des pathologies qui démontrent l’hypersensibilité de classe 2.

A
  • Anémie hémolytique
  • Goodpasture
  • Test de Coomb
79
Q

Décrit l’ADCC en hypersensibilité de type 2.

A
  • In this case, the bound antigen-antibody complex gets recognized by immune cells called natural killer cells, yeah.
  • The natural killer cell recognizes the Fc tail of the antibody and releases toxic
    granules.
  • These granules contain perforins which just like the MAC, form pores in the cell, except this time the pore also allows entry of enzymes that are like silent assassins called granzymes as well as granulysin which work together to cause cell death in an apoptotic or “quiet death” sort of way, such that there’s no surrounding inflammation.
80
Q

Exemple d’hypersensibilité de type 2 non cytotoxique?

A
  • When this happens it can change the way the cell is supposed to function.
  • Myasthenia gravis
  • Grave’s disease
81
Q

Décrit la réaction d’hypersensibilité de type 3.

A
  • Médié par des complexes immuns qui s’accumulent dans le sang
  • Activation du complément dans la lamina propria des vx
82
Q

Effet de l’activation du complément dans les vx?

A
  • Recrutement de neutrophiles
  • Anaphylatoxines augmentent la perméabilité des vx
83
Q

Exemple d’hypersensibilité de type 3?

A

Lupus
Glomérulonéphrite
Arthrite

84
Q

Décrit l’hypersensibilité de type 4.

A
  • Médié par les LT
  • Formation de TH1
  • Cascade inflammatoire en réaction au nickel
85
Q

A type IV hypersensitivity is also referred to as a delayed-type hypersensitivity, since it usually takes about ____ hours to recruit TH1 cells to the site of exposure

86
Q

Exemple d’hypersensibilité de type 4?

A

Arthrite rheumatoide
Sclérose
MII

87
Q

Décrit le rôle des cellules NK et CD8 dans l’hypersensibilité de type 4.

A
  • Se lie à un CMH1 mal exprimé
  • Tue la cellule
  • Présent dans le diabète de type 1 et la thyroide d’Hashimoto
88
Q

Est-ce que les glucides et les lipides peuvent créer une mémoire immunologique?

89
Q

Memory B cells live for up to __ years in a lymph node

90
Q

Anticorps des LB mémoire?

91
Q

Comment la réponse mémoire s’adapte à la réponse de base?

A
  • Now, because of somatic hypermutation, IgG antibodies created toward the end of the primary immune response typically have higher affinity than the IgM antibodies created early in the primary immune response.
  • These high affinity IgG antibodies therefore bind to Fc gamma receptor II on newly activated IgM producing B cells, inhibiting them from differentiating into plasma cells.
92
Q

Décrit la mémoire immunitaire des LT.

A
  • LT avec de IL7 survivent
  • CD45RA and CD45RO
93
Q

Décrit les LT mémoire central.

A

25 years and remain in the lymphoid tissue

94
Q

Décrit les LT mémoire effecteur.

A

Bougent dans le corps à la recherche de pathogène

95
Q

Que contient le SMAC?

A

p → LFA1
c → MHC1

96
Q

Décrit la synapse immunitaire des LT.

A

TCR se lie à MHC1
B7 se lie à CD28

97
Q

Dans l’ADCC, quel récepteur de la cellule NK se lie aux IgG?

98
Q

À quoi sert FOXP3?

A

Crée les Treg

99
Q

À quoi sert le CTLA4 des Treg?

A

Inhibe B7 sur les cellules présentatrice d’antigènes qui reconnaissent le soi

100
Q

Qu’est-ce qui se passe si un LT se lie à une cellule présentatrice d’antigène sans B7?

A

Anergie clonale

101
Q

Qu’est-ce qui se passe si un LT a de la difficulté à avoir de la co-stimulation?

A

Moins de IL2 et plus de Fas → mot

102
Q

Comment les LB font pour se réguler?

A
  • Si ils reconnaissent les antigènes du soi → jamais de liaison à un LT
  • Si pas de liaison → pas de maturation
103
Q

Décrit la réponse immunitaire aux bactéries.

A
  1. Cellule dendritique mange la bactérie
  2. Présentation sur un CMH2 au LB
  3. Le LB le présente à un LT → Th
  4. Le LB devient un plasmocyte
104
Q

Quel LT?
CD45RA

105
Q

Quel LT?
CD45RO

106
Q

What is the adaptive immune response specific for?

A

Each invader

The specificity arises from receptors that differentiate friendly bacteria and deadly pathogens via antigens.

107
Q

What are the key cells of the adaptive immune response?

A

Lymphocytes: B cells and T cells

These cells have unique antigen receptors.

108
Q

What is VDJ rearrangement?

A

A mechanism to generate diverse antigen receptors

It stands for variability, diversity, and joining.

109
Q

List the four key characteristics of VDJ rearrangement.

A
  • Multiple V, D, and J gene segments inherited
  • Random recombination of V, D, and J segments
  • Recombination inaccuracy leads to variation
  • Random reassortment of two chains
110
Q

What is the B cell receptor (BCR) essentially?

A

An antibody with a transmembrane part

It attaches to the surface of a B cell.

111
Q

What is the Fab region of the B cell receptor?

A

Fragment-antigen binding region

There are two Fab regions on every BCR.

112
Q

What determines the class of B cell receptor?

A

The constant region or Fc region

Examples include IgM or IgD.

113
Q

How does the T cell receptor (TCR) differ from the BCR?

A

TCR has only two chains and no secreted form

It has an alpha chain and a beta chain.

114
Q

What is the antigen binding site in TCRs?

A

The variable region (V region)

It only has one antigen binding site.

115
Q

What are hypervariable regions?

A

Segments of the V region that contribute to diversity

They form the actual antigen binding site.

116
Q

How many V, D, and J gene segments does an individual inherit for B cell heavy chains?

A

44 V segments, 27 D segments, 6 J segments

More segments exist for T cell receptors.

117
Q

What is the role of recombination signal sequences?

A

They flank points for DNA rearrangement

They guide the cutting and rearranging of DNA.

118
Q

What are the three parts of a recombination signal sequence?

A
  • Heptamer (7 nucleotides)
  • Spacer (12 or 23 nucleotides)
  • Nonamer (9 nucleotides)
119
Q

What enzymes are involved in VDJ rearrangement?

A
  • RAG1 and RAG2 (cut DNA)
  • Ku, DNA-protein kinase, Artemis (repair DNA)
  • DNA ligase IV (join DNA)
120
Q

What does terminal deoxynucleotide transferase (TdT) do?

A

Adds and removes nucleotides randomly

This process increases receptor diversity.

121
Q

What happens if the heavy or beta chain binds to the surrogate chain?

A

Signals the cell to proliferate

This occurs in B cells with VpreB and T cells with pre-T alpha.

122
Q

What is created during the random assortment of chains?

A

A light chain for B cells or an alpha chain for T cells

This follows the heavy or beta chain creation.

123
Q

What is tested after the light or alpha chain rearrangement?

A

If it binds to the heavy or beta chain

This ensures the cell is not self-reactive.

124
Q

What happens if a cell is self-reactive?

A

It rearranges the light or alpha chain until genetic material runs out

If it runs out, the cell dies.

125
Q

What is the primary function of the adaptive immune response?

A

It is highly specific for each invader due to unique receptors that differentiate friendly bacteria from pathogens.

126
Q

What are the key cells of the adaptive immune response?

A

Lymphocytes - the B and T cells.

127
Q

Where do B cells develop?

A

In the bone marrow.

128
Q

What process do B cells undergo to generate diverse receptors?

A

VDJ rearrangement.

129
Q

What is the B cell receptor essentially an example of?

A

An antibody with a transmembrane part.

130
Q

What are the two types of chains that make up the B cell receptor?

A

Heavy chains and light chains.

131
Q

What is the fragment of the B cell receptor that binds to the antigen called?

A

Fab region.

132
Q

What is the constant region of the B cell receptor referred to as?

A

Fc region.

133
Q

How many Fab fragments are present on each B cell receptor?

134
Q

What happens to the B cell receptor as the B cell develops into a plasma cell?

A

It gets secreted as an antibody with the same antigen specificity.

135
Q

How many major types of heavy chains are there in immunoglobulins?

136
Q

What are the five major types of immunoglobulins?

A
  • IgM
  • IgD
  • IgG
  • IgA
  • IgE
137
Q

What is the first antibody response made in all immune responses?

A

Immunoglobulin M (IgM).

138
Q

What percentage of serum immunoglobulin does IgM constitute?

A

Approximately 4%.

139
Q

What structural form does IgM take when serving as a B cell receptor?

140
Q

When IgM is secreted, what form does it take?

141
Q

What is the role of the J chain in IgM?

A

It promotes the polymerization of the pentamer by linking to the cysteines of the Fc regions.

142
Q

What is the valence of secreted IgM?

143
Q

Can IgM be made without T cell help?

144
Q

What is the most effective antibody at activating the complement pathway?

145
Q

What percentage of serum immunoglobulin does IgG make up?

146
Q

What is the structural composition of IgG?

A

Two gamma heavy chains and two light chains.

147
Q

What is the valence of IgG?

148
Q

What are the subclasses of IgG?

A
  • IgG1
  • IgG2
  • IgG3
  • IgG4
149
Q

What is the primary role of IgG in the immune response?

A

To serve as an opsonin.

150
Q

What is opsonization?

A

The process by which pathogens are coated with molecules to facilitate phagocytosis.

151
Q

What receptor do phagocytes use to bind IgG?

A

Fc gamma receptor.

152
Q

What is antibody dependent cell mediated cytotoxicity (ADCC)?

A

A mechanism by which natural killer cells kill virally infected cells using IgG.

153
Q

What unique ability does IgG have concerning the placenta?

A

It can cross the placenta.

154
Q

What percentage of serum immunoglobulin does IgA represent?

A

About 20%.

155
Q

What is the valence of IgA?

156
Q

Can IgA cross the placenta?

157
Q

What is the main antibody found in mucosal sites?

158
Q

What form does IgA take in mucosal sites?

159
Q

What is the role of the poly-Ig receptor in IgA transport?

A

It facilitates the transcytosis of IgA dimers across epithelial cells.

160
Q

What are the two forms of IgA?

161
Q

What important role does IgA play in infants?

A

It neutralizes pathogens in the gastrointestinal tract via breast milk.

162
Q

What is the primary function of IgE?

A

To mediate allergic and anti-parasitic responses.

163
Q

What makes up only about 0.004% of total serum immunoglobulin?

164
Q

What type of receptors does IgE bind to?

A

Fc epsilon receptors.

165
Q

What happens when IgE binds to its receptors on mast cells?

A

It triggers granule release.

166
Q

What is the role of IgD in B lymphocytes?

A

It signals that they are ready to leave the bone marrow.

167
Q

What percentage of serum immunoglobulin does IgD constitute?

A

Less than 1%.

168
Q

What is the valence of IgD?

169
Q

What is the role of antigens in the adaptive immune response?

A

Antigens are unique parts of pathogens that cells of the adaptive immune response differentiate to identify invaders.

Antigens trigger specific immune responses through their recognition by lymphocytes.

170
Q

What are the key cells involved in the adaptive immune response?

A

The key cells are lymphocytes, specifically B cells and T cells.

Lymphocytes have unique antigen receptors called B cell receptors (BCR) and T cell receptors (TCR).

171
Q

What process do B cells and T cells undergo to generate diverse receptors?

A

Both B cells and T cells undergo VDJ rearrangement.

This process allows for a massive diversity of antigen receptors.

172
Q

What is somatic hypermutation?

A

Somatic hypermutation is a process that further enhances the diversity of B cell receptors after activation.

It leads to stronger and more specific responses to antigens.

173
Q

What is affinity maturation?

A

Affinity maturation is the process by which B cells develop stronger and more specific responses to antigens through mutation and selection.

This process occurs during the rapid proliferation phase of activated B cells.

174
Q

What are the two general parts of a B cell receptor (BCR)?

A

The two parts are the variable region and the constant region.

The variable region binds antigen, while the constant region determines the antibody class.

175
Q

What triggers the activation of B cells?

A

Activation occurs when a foreign antigen binds and cross-links adjacent BCRs.

This initiates a cascade of events for B cell proliferation and differentiation.

176
Q

What is the role of CD4+ helper T cells in B cell activation?

A

CD4+ helper T cells bind to presented antigens and express CD40 ligand, triggering B cell activation events.

This includes the activation of the enzyme Activation Induced cytidine deaminase (AID).

177
Q

What condition arises from a lack of Activation Induced cytidine deaminase (AID)?

A

The condition is known as Hyper IgM immunodeficiency.

Individuals with this condition have difficulty producing antibodies other than IgM.

178
Q

What is the function of AID in B cells?

A

AID allows B cells to make cuts in DNA, facilitating class switching and somatic hypermutation.

This enzyme is specific to B cells and is crucial for antibody class switching.

179
Q

Describe mismatch repair in the context of somatic hypermutation.

A

Mismatch repair involves MSH2 and MSH6 proteins fixing DNA by removing uridine and adjacent nucleotides, leading to potential mutations.

This process is error-prone and can introduce mutations into the BCR.

180
Q

What happens during base excision repair?

A

Uracil-DNA glycosylase removes uracil, and random nucleotides may be inserted during DNA replication, leading to mutations.

This can also affect the specificity of the BCR.

181
Q

How do mutations in the variable region of BCRs affect antibody affinity?

A

Mutations can increase or decrease the affinity of BCRs for antigens.

Higher affinity BCRs are selected for survival during affinity maturation.

182
Q

What leads to the natural selection of B cells during the immune response?

A

B cells with higher affinity BCRs survive and proliferate while those with low affinity die out.

This mimics natural selection on a cellular level.

183
Q

What occurs to the amount of antigen during the immune response over time?

A

The amount of antigen decreases as the immune system clears the infection.

This reduction promotes the selection of B cells with the highest affinity BCRs.

184
Q

Fill in the blank: The process by which B cells change from producing IgM to IgG, IgA, or IgE is called _______.

A

class-switching.

This process is facilitated by the enzyme AID.