Faculty Leader: Tiffany Scharschmidt

Microbiology 204 Discussion Session #4 Oct 25, 2017 1-2:30PM Room: CL220/223 Faculty leader: Tiffany Scharschmidt

Sabouri et al IgD attenuates IgM induced B-cell anergy. Nat Commun 7:13381, 2016

Everyone should read this paper before coming to class. You do not need to look at the Supplemental Material file.

LEARNING OBJECTIVES: To understand mechanisms involved in B-cell receptor signaling in IgM+ versus IgD+ cells.

STUDENT ASSIGNMENTS 1. Discussion leader (see instruction page for advice on leading the discussion).

2. Please review the expression pattern of IgM versus IgD during normal B-cell development. Which B-cell types express which receptors. The role of IgD on B-cells is unclear – describe the phenotype of the IgD knockout mouse.

3. This paper depends on use of transgenic mice that carry the anti-HEL (hen egg lysomze) IgM or IgD transgenes in the setting of ubiquitous expression of HEL (soluble form). This is the MD4:ML5 system (and variants). This system to study B-cell anergy was established years ago. Please describe these mouse lines. What happens if a transgene expresses a membrane bound form of HEL?

4. Present data from Fig. 2a-e. These data demonstrate that IgD+ anergic B-cells respond well to strong immune challenge (HEL+SRBC) to form germinal centers, while IgD- are weaker. There are two explanations for this. One is presented in Fig. 2f-h, but what is the other (the answer is probably shown in Fig. 2a – receptor level expression).

5. Lets skip Fig.3. Present data from Fig. 4. This is a very complex transcriptional profile characterization between all the different B-cell types, either naïve or anergic. What are some of the overall conclusions from this comparison. Remember that the IgD-deficient B-cells have only ½ or less the amount of surface antigen-binding IgM BCRs than IgD+ cells (see Fig. 2a).

6. Present data from Fig. 5 which using FACs to verify the expression of three genes picked up in the RNA profiling from the previous figure.

7. Fig. 6 uses FACs to follow syndecan-1 expression on B-cells from the dmit strain that lacks IgD. What do these data show?

8. This paper demonstrates that expression of IgD on mature B-cells limits the anergic phenotype of self-reactive B-cells. It also allows these anergic B-cells to accumulate. This is great, because it allows us to have B-cells that may be close to being self-reactive, but which are normally turned off. In the setting strong immune challenge, these B cell clones could go through the germinal center and mutate away from self to provide new specifies against foreign pathogens. There is one big problem with this paper: mechanism. The authors say little about this Discussion. Please review potential molecular mechanisms by which IgD could limit IgM self-reactivity. 9. If this paper is correct, what do you think would happen if IgD knockout mice were given strong infectious challenge? Do you think they may get autoimmunity?

Student assignment #s

1. Kristoffer Leon 10. Casey Burnett 2. Lauren Mchenry 11. Karen Chan 3. Tara Mcintyre 12. Irene Chen 4. Geil Merana 13. Antonia Gallman (will be out) 5. Andrew Ng 14. Kamir Hiam 6. Ramiro Patino 7. Anthony Venida 8. Camillia Azimi 9. Ian Boothby

(NOTE : if you will miss a discussion session, inform Dr. Lowell in advance and you won’t be given an assignment that week; if assignments have already been made, you should make a trade with one of your classmates who does not have an assignment that week so that your assignment is covered).