Frog's DCs have it all in one.

Although the amphibian Xenopus laevis produces antibodies as diversified as those from mammals in the primary repertoire, antibody affinity maturation after immunization is relatively poor and has been associated with a poor B cell selection of AID-mediated hypermutations and lack of germinal centers in the spleen, the only secondary lymphoid organ of this amphibian. In this issue of the European Journal of Immunology, Neely et al., [Eur. J. Immunol. 2018. 48: 430-440] have unveiled the role of distinctive dendritic cell (DC) subset, XL cells, which have the capacity to acquire and retain native antigens for B cell maturation. The complementary evidence presented by this study (immunohistology, tracing antigen complexes, flow cytometry analysis and gene expression profiles of sorted XL cells) provides novel fundamental insights into a major evolutionary step in functional and cellular specialization of DC and follicular dendritic cells (FDCs) in regulating B cell responses.