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

Macrophage (M )-lineage cells are integral to the immune defences of all vertebrates, including amphibians. Across vertebrates, M 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 ( ) M s differentiated with CSF1 and IL34 are morphologically, transcriptionally and functionally distinct. Notably, mammalian M s share common progenitor population(s) with dendritic cells (DCs), which rely on fms-like tyrosine kinase 3 ligand (FLT3L) for differentiation while IL34-M s exhibit many features attributed to mammalian DCs. Presently, we compared CSF1- and IL34-M s with FLT3L-derived DCs. Our transcriptional and functional analyses indicated that indeed the frog IL34-M s and FLT3L-DCs possessed many commonalities over CSF1-M s, including transcriptional profiles and functional capacities. Compared to CSF1-M s, the IL34-M 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 and generating re-exposure immune responses against . Further analyses of non-mammalian myelopoiesis akin to those described here, will grant unique perspectives into the evolutionarily retained and diverged pathways of M and DC functional differentiation. This article is part of the theme issue 'Amphibian immunity: stress, disease and ecoimmunology'.