2.3 Ab genetics

how can we make billions of B cells each capable of making a unique antibody protein?

the generation of antigen-receptor diversity

antigent independent mechanisms:

VDL recmbo (germline, combinatorial, junction imprecise joinig) (DNA level)

antigen dependent mechanisms:

somatic hypermutation, class switch recombo

explain IgM and IgG during primary response:

IgM class switches to IgG

define V(D)J recombo

DNA rearrangement mechanism that creates many billions of BCRs and TCRs relatively few BCR and TCR genes

what two proteins mediate V(D)J recombo?

RAG-1 RAG-2

what two primary lymphoid organs express the two proteins that mediate V(D)J?

Developing B cell in bone marrow and developing T cell in thymus

you would find expression of RAG 1 and 2 required for cutting and pasting of DNA

V(D)J recombo is a (BLANK) process

costly, most developing B and T cells fail to make receptor and die, random

what types of genes for kappa light chain?

about 40 Vk and 5 Jk genes with Ckappa

what types of genes fpr the Ig heavy chain?

50 Vh genes

25 Dh genes

6 Jh genes

with Cmu and Cdelta

Simple terms what is the goal of V(D)J

re-assort genes to create varying variable regions! the uniqueness

the three generations of antibody diversity:

1. germline: multiple inherited V, D, J

2. combinatorial: V +D + J and H + L

3. junctional imprecise joining and TdT (terminal deoxyribonucleotidyl transferase)

happening in select cells w certain part of chromosome

what would happen if RAG-1 or RAG-2 are missing?

no adaptive immunity; no B and T cells SIDS

complete deficiency in either results in absence of both

key points of V(D)J recombo?

V(D)J recombo akes place in DNA

meaning when B or T cell goes under antigen selectin, the randomly made receptor is retained in the clone, you cannot make a certain B or T cell.

full V(D)J definition from lecture:

is a lymphocyte-specific process that mediaes the recombo of V, D, J segments within an antigen receptor loci to give rise to diverse set of antigen-specific receptors

which loci do B cells rearrange?

Ig loci (bone marrow)

Igh and either Igkappa or Iglamba

which loci do T cells rearrange?

TCR loci (thymus)

TCRalpha and beta

Do T cells play a role in somatic hypermutation or class switch recombo?

No just B

what happens to antigen binding B cells after V(D)J?

undergo SHM nd CSR

explain somatic hypermutation (SHM)

• affinity: strength of binding btwn Ab combing site and its epitope aka association constant

  • higher affinity = less amnt Ab needed

• SMH leads to affinity maturation via point mutations in Ab variable regions

• average affinity of Ab response can increase 100-1000 fold over time due to SHM and selection

class switch recombination:

genetic process of changing isotypes

what enzyme mediates both CSR and SHM?

AID (activation-induced cytidine deaminase)

both happen in cell at the same time when colonal expansion happens

3 outcomes of point mutation in variable region? (one Ab dividing)

no longer works

works better (this one divides more)

losses affinity

if Abs come from same clone that means …

they have the identical variable region; those of same isotype can have same variable region

T or F: Antibodies of the same isotype (e.g., IgG, IgA) can have the same variable region if they are produced by the same B cell or derived from the same clone of B cells

True

memory cells …

… cut out, move and degrade the unneeded DNA that belonged to IgM or IgD meaning it stays that said new isotype

V(D)J the same though meaning still binds said antibody just the effector style changes

what would happen if AID does not work?

no/limited class switch, cannot increase affinity of Ab, and high IgM levels

• tons of IgM made; hyper IgM syndrome, no ADCC, ADCP, etc.

• treat w IVIg: intravenous immunoglobulin

IgD significance:

marker of naive cell; that is pretty much it