m121 lec 8 - B cell activation and isotype switching

we need immune system [1] to make [2] of different specificities to detect variety of [3]

immune system discriminates between self and non-self, and destroys everything non-self

• learns to recognize and ignore YOU, but attack everything else

• our good microbes are considered “self”

[4] immunity

• [5] – [2], polysaccharide coat, lipids that [6] cells can only recognize, which is why you need [2]

• [7] – Ag specific

first, [8] B cells (IgM+, IgD+, no [2] secretion yet) recognize an Ag

second, helper [6] cells activate the B cell

then, activated B cells go through [9] [9] (process of keeping only useful B cells), then differentiates into four pathways

• effector cells: [10] cells make [2] (IgM initially → [11] [11])

• can secrete IgG instead through [11] [11]

• [12] [13]: higher [12] IgG produced, driven by [6] cell help

• differentiation into [14] B cell; vaccines train immune system with small amount of Ag

1. diversity

2. Ab

3. epitopes

4. humoral

5. innate

6. T

7. adaptive

8. naive

9. clonal expansion

10. plasma

11. isotype switching

12. affinity

13. maturation

14. memory

pt 1: B cell Ag [5] and signaling (BCR)

BCR complex (Y-shaped protein [1] + [2] and [3]) signals to B cell for detection of non-self

• [1] (membrane-bound Ig) interacts with [2] and [3] that are also on B cell → sends signals into B cell

• on [2]/[3] are [4] [4]-[4] [4] [4] (ITAMs) that trigger an activation cascade

when the B cell [5] (BCR)’s [1] binds Ag, that triggers the [6] of [4] [4]-[4] [4] [4] domains in [2] and [3]

• [6] events involve [7] [7] (enzymes) – [8], [9], and [10]

  • [11] [11]: [12]-[12] activation occurs, which leads to two pathways

    • increased intracellular [13] levels → [14] enzyme

    • [15] → [16] enzyme

• the [17] molecule, [18], (green) binds and sends a downstream signal to other molecules via cross-linking

  • [11] [11]: [19], [20] activation

    • then [21], [22] kinase (enzyme) activation

inside the [23], all of the latest signals ([14], [16], [21]) converge to target [24] factors – [25], [26], and [27] for gene activation that expresses:

• cell [28]

• [29] [5] expression

• [29]

• proteins for interaction with [30] cells

• enhance [31] secretion

1. mIg

2. Iga

3. Igb

4. immunoreceptor tyrosine-based activation motifs

5. receptor

6. phosphorylation

7. tyrosine kinases

8. Fyn

9. Lyn

10. Blk

11. secondary messengers

12. PLC-gamma

13. calcium

14. calcineurin

15. DAG

16. PKC

17. adaptor

18. Syk

19. Ras

20. Rac

21. ERK

22. JNK

23. nucleus

24. transcription

25. NFAT

26. NFkB

27. AP-1

28. proliferation

29. cytokine

30. T

31. Ab

pt 2: B cell Ag [1] and signaling (BCR)

[2] (C’) assists B cell activation

left side:

• pathogen has [3] that interacts with B cell’s [4]

• then, factor [5] cleaves [3] to make iC3b, which is further cleaved to make [6] on the pathogen

right side:

• then, we have BCR complex ([7] + [8] and [9]), whose [7] binds to pathogen 

• [10] (aka [14]) on the B cell [15] also interacts with [6] on pathogen

• the B cell [15] also includes [11] and [12] 

all of these (C’ + B cell signaling units) work together for [13] B cell activation upon binding Ag

1. receptor

2. complement

3. C3b

4. CR1

5. I

6. C3d

7. mIg

8. Iga

9. Igb

10. CR2

11. CR19

12. CR81

13. enhanced

14. CD21

15. coreceptor

[1] cell help

“are you sure it’s a non-self?” – need to check before [2] cell/[3] replication begins

[2] cell has its own [4] (BCR), and [5] molecule, and [6] [4]

• [2] cell sends positive signals to a [1] cell

• in response, the [1] cell can provide help to the [2] cell

[1] cell has [7] and makes [6]

• non-specific activation: [7] on [1] cell binds [5] on [2] cell

• [8] (specific activation): [1] cell’s [6] can bind [2] cell’s [6] [4] and thereby send positive signals back to [2] cell

• both of these signals from the [1] cell leads to:

  • further [2] cell activation

  • increased [3] production

  • [9]/[10] switching

1. T

2. B

3. Ab

4. receptor

5. CD40

6. cytokine

7. CD40L

8. crosstalk

9. isotype

10. class

pt 1: [1] switching

it’s good to have different [1]

• [3] – [4] activation

• [5] – [6] via FcGR that sits on cell surface + [7] (MO)

• [8] – involved with [9] via FcER + [10] to kill helminths (worms)

another method of cutting & pasting DNA for [2] of generated [11], starting right after VDJ, on the [12] region of the [13] chain

• there is a [12] region for each Ig [1] (MEGAD, but memorize as MDGAE order, or Dr. Gae idk)

• within the DNA are [14] regions between Ig [12] regions

  • [15] right after Cm gives you mRNA for IgM

  • [15] after Cd gives you mRNA for IgM/IgD (which are expressed by immature B cells)

  • [15] everything out up to Ce leaves you with only mRNA for IgE; no more switching after this point

  • if [15] out only occurred up to Cg, then at least you’d still have Cg + Ca + Ce to [14] out

DNA [15] done by [16], whose activity is increased by [17]-[18] signaling ([19] cell help). [1]/class switching is NOT random; DNA [15] determined by [20]

• if [19] cell releases [20] [21]-[21] → IgG

• if [19] cell releases [20] [22] → IgE and IgG

1. isotype

2. diversity

3. IgM

4. complement

5. IgG

6. phagocytosis

7. macrophage

8. IgE

9. allergies

10. eosinophil

11. Ab

12. constant

13. heavy

14. switch

15. splicing

16. AID

17. CD40

18. CD40L

19. T

20. cytokine

21. IFN-gamma

22. IL-4

pt 2: [1] switching

how do we know if the [2] is going to be [3]-[3] or [4]?

• starting with the [5] RNA, you can do [6] RNA [7] to cut out specific parts of the [5] RNA and create mRNA that encodes either [3]-[3] or [4] Ab

1. isotype

2. Ab

3. membrane-bound

4. secreted

5. primary

6. alternative

7. splicing

remember, each B cell makes only one [1] of [2] and recognizes only one Ag. but, the [3] can change – can make IgM/IgG/IgE. the binding of Ag to the [4] (a [5]-[5] [2]) triggers the whole signaling cascade. once activated, the B cell can transform and [6] the [4] as a soluble [2] to fight infections.

1. specificity

2. Ab

3. isotype

4. BCR

5. membrane-bound

6. secrete