DOCK8 deficiency causes a skewing to type 2 immunity in the gut with expansion of group 2 innate lymphoid cells.

Dedicator of cytokinesis 8 (DOCK8) is a guanine nucleotide exchange factor (GEF) for Cdc42. In humans, homozygous or compound heterozygous deletions in DOCK8 cause a combined immunodeficiency characterized by various allergic diseases including food allergies. Although group 2 innate lymphoid cells (ILC2s) contribute to the development of allergic inflammation by producing interleukin (IL)-5 and IL-13, the role of ILC2s in DOCK8 deficiency has not been fully explored. With the use of cytometry by time-of-flight (CyTOF), we performed high-dimensional phenotyping of intestinal immune cells and found that DOCK8-deficient (Dock8-/-) mice exhibited expansion of ILC2s and other leukocytes associated with type 2 immunity in the small intestine. Moreover, IL-5- and IL-13-producing cells markedly increased in Dock8-/- mice, and the majority of them were lineage-negative cells, most likely ILC2s. Intestinal ILC2s expanded when DOCK8 expression was selectively deleted in hematopoietic cells. Importantly, intestinal ILC2 expansion was also observed in Dock8VAGR mice having mutations in the catalytic center of DOCK8, thereby failing to activate Cdc42. Our findings indicate that DOCK8 is a negative regulator of intestinal ILC2s to inhibit their expansion via Cdc42 activation, and that deletion of DOCK8 causes a skewing to type 2 immunity in the gut.

S100A4 Protein Is Essential for the Development of Mature Microfold Cells in Peyer's Patches.

Intestinal microfold cells (M cells) in Peyer's patches are a special subset of epithelial cells that initiate mucosal immune responses through uptake of luminal antigens. Although the cytokine receptor activator of nuclear factor-κB ligand (RANKL) expressed on mesenchymal cells triggers differentiation into M cells, other environmental cues remain unknown. Here, we show that the metastasis-promoting protein S100A4 is required for development of mature M cells. S100A4-producing cells are a heterogenous cell population including lysozyme-expressing dendritic cells and group 3 innate lymphoid cells. We found that in the absence of DOCK8, a Cdc42 activator critical for interstitial leukocyte migration, S100A4-producing cells are reduced in the subepithelial dome, resulting in a maturation defect of M cells. While S100A4 promotes differentiation into mature M cells in organoid culture, genetic inactivation of S100a4 prevents the development of mature M cells in mice. Thus, S100A4 is a key environmental cue that regulates M cell differentiation in collaboration with RANKL.