An IL-1beta-dependent switch in innate mucosal immunity?

Single-cell atlas of the small intestine throughout the human lifespan demonstrates unique features of fetal immune cells

Proper development of mucosal immunity is critical for human health. Over the past decade, it has become evident that in humans, this process begins in utero. However, there are limited data on the unique features and functions of fetal mucosal immune cells. To address this gap, we integrated several single-cell ribonucleic acid sequencing datasets of the human small intestine (SI) to create an SI transcriptional atlas throughout the human life span, ranging from the first trimester to adulthood, with a focus on immune cells. Fetal SI displayed a complex immune landscape comprising innate and adaptive immune cells that exhibited distinct transcriptional programs from postnatal samples, especially compared with pediatric and adult samples. We identified shifts in myeloid populations across gestation and progression of memory T-cell states throughout the human lifespan. In particular, there was a marked shift of memory T cells from those with stem-like properties in the fetal samples to fully differentiated cells with a high expression of activation and effector function genes in adult samples, with neonatal samples containing both features. Finally, we demonstrate that the SI developmental atlas can be used to elucidate improper trajectories linked to mucosal diseases by implicating developmental abnormalities underlying necrotizing enterocolitis, a severe intestinal complication of prematurity. Collectively, our data provide valuable resources and important insights into intestinal immunity that will facilitate regenerative medicine and disease understanding.

Receptors for non-MHC ligands contribute to uterine natural killer cell activation during pregnancy in mice

INTRODUCTION

Activated uterine natural killer (uNK) cells are abundant in early human and mouse decidual basalis. In mice, distinct uNK cell subsets support early endothelial tip cell induction, the pruning of new vessels and initiation of spiral arterial modification. While genetic studies indicate that NK/uNK cell activation via receptors recognizing Class I MHC-derived peptides promotes human pregnancy, roles for other activation receptors expressed by NK cells, such as the aryl hydrocarbon receptor (AHR) and natural cytotoxicity receptors (NCR) are undefined in human or mouse pregnancies.

METHODS

Expression of AHR and NCR1 (ortholog of human NKp46) by gestation day (gd)10.5 mouse uNK cell subsets was measured by quantitative real-time RT-PCR. Early implantation sites from mice lacking expression of either receptor were examined histologically.

RESULTS

Gd10.5 uNK cell subsets, separated by reactivity to Dolichos biflorus agglutinin lectin, differed in relative transcript abundance for Ahr and Ncr1. Quantitative histology revealed that, in comparison to C57BL/6 controls, implant sites from gd10.5 Ahr(-/-) and gd6.5-12.5 UkCa:B6.Ncr1(Gfp/Gfp) mice had normal uNK cell abundance but the uNK cells were smaller than normal and unable to trigger spiral arterial remodeling. Whole mount immunohistochemistry comparisons of viable, gd6.5-8.5 Ncr1(Gfp/Gfp) and C57BL/6 implant sites revealed deficits in implant site angiogenesis and conceptus growth in Ncr1(Gfp/Gfp).

DISCUSSION

In mice, activation of AHR and of NCR1 by endogenous, as yet undefined ligands, contributes to uNK cell activation/maturation and angiogenic functions during early to mid-gestation pregnancy. MHC-independent activation of uNK cells also likely makes critical contributions to human pregnancy success.

Lineage relationships of human interleukin-22-producing CD56+ RORγt+ innate lymphoid cells and conventional natural killer cells

Human interleukin (IL)-22-producing RORγt(+) innate lymphoid cells (ILC22) and conventional natural killer (cNK) cells are present in secondary lymphoid tissues. Both have an immunophenotype corresponding to stage III NK progenitors (CD56(+/-)CD117(high)CD94(-)). Using an in vitro differentiation and primary human tissues, we investigated their developmental relationships. cNK cells showed a CD56(+)CD117(+)CD7(+/-)LFA-1(high) phenotype and expressed surface receptors, cytokines, and transcription factors found on mature cNK cells. In contrast, ILC22 cells were contained within the CD56(+)CD117(high)CD94(-)CD7(-)LFA-1(-) fraction and produced IL-22, IL-8, and granulocyte macrophage colony stimulating factor. Although ILC22 cells expressed NKp44 and CD161, they lacked most other NK receptors and NK-associated transcription factors (T-bet and Eomes) and were incapable of interferon-γ production or cytotoxic responses. Most purified CD56(+)CD117(+)CD7(+/-)LFA-1(-) remained as ILC22 cells and never became cNK cells. In the absence of IL-15, CD34(+) cells showed a complete block in cNK differentiation and instead gave rise to a CD56(+) population of ILC22 cells. Conversely, in the absence of IL-7 and stem cell factor, cNK cells were generated but ILC22 cells showed minimal differentiation. Although human ILC22 cells and cNK progenitors have a phenotype that overlaps with stage III NK progenitors, they have unique cytokine requirements and can be distinguished by LFA-1 expression.