Abstract
The human fetal immune system must protect the infant against the sudden exposure to a large variety of pathogens upon birth. While it is known that the fetal immune system develops in sequential waves, relatively little is known about the composition of the innate and adaptive immune system in the tissues. Here, we applied high-dimensional mass cytometry to profile the immune system in human fetal liver, spleen, and intestine. With Hierarchical Stochastic Neighbor Embedding (HSNE) we distinguished 177 distinct immune cell clusters, including both previously identified and novel cell clusters. PCA analysis indicated substantial differences between the compositions of the immune system in the different organs. Through dual t-SNE we identified tissue-specific cell clusters, which were found both in the innate and adaptive compartment. To determine the spatial location of tissue-specific subsets we developed a 31-antibody panel to reveal both the immune compartment and surrounding stromal elements through analysis of snap-frozen tissue samples with imaging mass cytometry. Imaging mass cytometry reconstructed the tissue architecture and allowed both the characterization and determination of the location of the various immune cell clusters within the tissue context. Moreover, it further underpinned the distinctness of the immune system in the tissues. Thus, our results provide evidence for early compartmentalization of the adaptive and innate immune compartment in fetal spleen, liver, and intestine. Together, our data provide a unique and comprehensive overview of the composition and organization of the human fetal immune system in several tissues.
Highlights
The notion of phenotypical and functional differences between the fetal and adult immune system has been widely accepted
To obtain singlecell suspensions from the lamina propria, the intestines were rinsed with HBSS and incubated with 15 mL Iscove’s Modified Dulbecco’s Medium (IMDM; Lonza) supplemented with 10% fetal calf serum (FCS), 10 U/mL collagenase IV (Worthington), 200 μg/mL DNAse I grade II (Roche Diagnostics), at 37◦C overnight, after which cell suspensions were filtered through a 70 μm nylon cell strainer
Fetal liver and spleen tissues were cut into small pieces filtered through a 70 μm nylon cell strainer and the immune cells were isolated with FicollPaqueTM density gradient
Summary
The notion of phenotypical and functional differences between the fetal and adult immune system has been widely accepted. T cells have been identified as early as 10 weeks of gestation while Foxp3+CD4+ regulatory T (Treg) cells, whose generation is mainly driven by maternal alloantigens, have been observed in different fetal tissues [4]. It has been shown that human fetal dendritic cells in spleen, skin, thymus, and lung promote prenatal T-cell immune suppression [5]. Several studies have provided evidence for the existence of memorylike T (Tm) cells in fetal spleen [6], skin [7], intestine [8, 9], and cord blood [10], which produce pro-inflammatory cytokines such as IFN-γ and TNF-α, suggesting functional maturation of T cells in utero. The fetal immune system has both pro-inflammatory and immune suppressive capacity
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