Single-cell 5' RNA sequencing of camelid peripheral B cells reveals cellular basis of heavy-chain antibody production

Camelids are capable of producing both conventional tetrameric antibodies (Abs) and dimeric heavy-chain antibodies (HCAbs). While B cells generating these two types of Abs exhibit distinct B-cell receptors (BCRs), it remains unclear whether these two B cell populations differ in their phenotypes and developmental processes. Here, we collected eight PBMC samples before and after immunization from four Bactrian camels and conducted single-cell 5 RNA sequencing. We characterized the functional subtypes and differentiation trajectories of circulating B cells in camels, including native B cells, memory B cells, intermediate B cells, atypical B cells, and plasma cells. Additionally, we reconstructed single-cell BCR sequences and revealed the IGHV and IGHC gene types. We found that B cells expressing variable genes of HACbs (VHH) were widely present in various functional subtypes and showed highly overlapping differentiation trajectories to B cells expressing variable genes of conventional Abs (VH). After immunization, the transcriptional changes in VHH+ and VH+ B cells were also largely consistent. Our study elucidates the cellular context of HCAb production in camels, and lays the foundation for the development of single B cell-based nanobody screening.