Mass cytometry reveals the myeloid subset architecture of the human spleen
Benjamin J Stewart1, John Ferdinand1, Nikitas Georgakopoulos2 , Kourosh Saeb-Parsy2, Menna R Clatworthy1*
1Department of Medicine and 2Department of Surgery, University of Cambridge
Background: The myeloid lineage includes several subsets of innate immune cells; neutrophils are the dominant circulating phagocyte, whilst mononuclear phagocytes (MNP), comprising macrophages and dendritic cells, are predominantly tissue-resident, occupying secondary lymphoid organs (lymph node and spleen) and peripheral tissues. Myeloid immune cell networks in human tissues are currently incompletely characterised. We sought to examine the immune landscape in human spleen, with a focus on myeloid cells.
Methods: We acquired tissue from N=9 deceased human organ donors, and performed CyTOF with a myeloid-biased, 32 surface marker panel. We applied non-linear dimensionality reduction (tSNE) and unsupervised clustering to the data.
Results: There was significant heterogeneity in the cellular composition of spleens between donors and particularly in the size of the neutrophil population. Using a graph-based clustering approach, we identified two distinct subsets of MNP and four neutrophil subsets. The larger MNP subset (MNP1) was CD11c/MHCII+. In contrast, a smaller subset (MNP2) lacked many classical MNP markers but had high expression of CD38, a marker ascribed to recently activated non-classical monocytes. Our approach was also able to identify rarer plasmacytoid dendritic cells.
In a spleen obtained from a donor with untreated Goodpasture’s syndrome (an autoantibody-mediated disease) we observed an expansion of MNP1, implicating these cells in antibody-mediated inflammation. Of relevance to ongoing efforts to map tissue cellular networks, we demonstrated that freezing samples obliterates the contribution of neutrophils to the immune landscape.
Conclusion: Our findings establish the structure of the human splenic myeloid immune cell network, and illustrate the potential of interrogating high dimensional single cell phenotypes in the study of human disease.