Single-cell atlas of splenocytes reveals a critical role of a novel plasma cell-specific marker Hspa13 in antibody class-switching recombination and somatic hypermutation

Our previous study had shown that member 13 (Hspa13) of heat shock protein family A (Hsp70) promotes plasma cell (PC) production and antibody secretion. To further explore Hspa13 expression and function, we combined single-cell RNA-sequencing and antigen receptor lineage (BCR) analysis to characterize sheep red cellprimed splenocytes. The single-cell transcriptional profiles revealed that Hspa13 is specifically and highly expressed in PCs. These results suggest that Hspa13 is a novel PC-specific marker. In terms of its function, we found that the CD19cre-mediated conditional knock-out (cKO) of Hspa13 reduced the expression of Ebi3 and IL10 in PCs. Ebi3 and IL-10 are important factors in IL-4-secreting type 2 helper T cell (Th2) activation and differentiation. As expected, we found that the Hspa13 cKO reduced IL-4-expressing follicular helper T (Tfh2) cells. Finally, the single-cell antigen receptor analysis demonstrated that the Hspa13 cKO reduced the Aicdamediated antibody class-switching recombination (CSR) and somatic hypermutation (SHM) in germinal centers (GCs) B cells. Altogether, the single-cell atlas of splenocytes revealed a critical indirect role for the novel PCspecific marker Hspa13 in CSR and SHM in GC B cells by promoting Ebi3 and IL-10 expression in PCs to induce IL-4-expressing Tfh2 cells. Further exploration of Hspa13 expression and function will provide valuable clues for how to use Hspa13 in the treatment of autoimmune diseases.

Automated summary

The study showed that Hspa13 is specifically and highly expressed in plasma cells, acting as a novel PC-specific marker. Knock-out of Hspa13 in plasma cells led to reduced expression of Ebi3 and IL10, affecting the generation of IL-4-expressing Tfh2 cells. Single-cell antigen receptor analysis also demonstrated that Hspa13 knockout affects antibody class-switching recombination and somatic hypermutation in GC B cells.