Detalle de: Individual B cells transcribe multiple rearranged immunoglobulin light chains in teleost fish

B cells express a unique antibody protein which comprises two pairs of immunoglobulin (Ig) heavy (H) and light (L) chains. In addition to an invariable constant (C) region, IgH and IgL chains encompass a variable (V) region mediating antigen binding. This unique region stems from Ig V(D)J gene recombination, which generates diversity by assembling these gene segments into V H DJ H and V L J L genes. To ensure that one B cell only expresses one antibody, V H DJ H rearrangement occurs only in one IgH locus (allelic exclusion), whereas V L J L rearrangement only in either the κ or λ locus (isotype exclusion). However, teleosts express multiple IgLs encoded by distinct C L genes. Using single-cell transcriptomics, we have demonstrated the transcription of distinct rearranged V L J L C L genes in single rainbow trout B cells. Our results highlight the laxity of isotype exclusion in teleosts and strongly suggest that fish B cells can produce antibodies of different specificities.