A perspective into the relationships between amphibian (Xenopus laevis) myeloid cell subsets

Macrophage (M phi)-lineage cells are integral to the immune defences of all vertebrates, including amphibians. Across vertebrates, M phi differentiation and functionality depend on activation of the colony stimulating factor-1 (CSF1) receptor by CSF1 and interluekin-34 (IL34) cytokines. Our findings to date indicate that amphibian (Xenopus laevis) M phi s differentiated with CSF1 and IL34 are morphologically, transcriptionally and functionally distinct. Notably, mammalian M phi s share common progenitor population(s) with dendritic cells (DCs), which rely on fms-like tyrosine kinase 3 ligand (FLT3L) for differentiation while X. laevis IL34-M phi s exhibit many features attributed to mammalian DCs. Presently, we compared X. laevis CSF1- and IL34-M phi s with FLT3L-derived X. laevis DCs. Our transcriptional and functional analyses indicated that indeed the frog IL34-M phi s and FLT3L-DCs possessed many commonalities over CSF1-M phi s, including transcriptional profiles and functional capacities. Compared to X. laevis CSF1-M phi s, the IL34-M phi s and FLT3L-DCs possess greater surface major histocompatibility complex (MHC) class I, but not MHC class II expression, were better at eliciting mixed leucocyte responses in vitro and generating in vivo re-exposure immune responses against Mycobacterium marinum. Further analyses of non-mammalian myelopoiesis akin to those described here, will grant unique perspectives into the evolutionarily retained and diverged pathways of M phi and DC functional differentiation.This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'.

Automated summary

The study found that two different types of amphibian macrophage (M phi) cells have similar transcriptomes and functions, resembling FLT3L-derived frog dendritic cells (DCs) and CSF1-M phi, respectively. These findings provide unique insights into the evolutionarily retained and diverged pathways of M phi and DC functional differentiation.