Mass cytometry enables high-dimensional, single-cell analysis of cell type and state. In mass cytometry, rare earth metals are used as reporters on antibodies. Analysis of metal abundances using the mass cytometer allows determination of marker expression in individual cells. Mass cytometry has previously been applied only to cell suspensions. To gain spatial information, we have coupled immunohistochemical and immunocytochemical methods with high-resolution laser ablation to CyTOF mass cytometry. This approach enables the simultaneous imaging of 32 proteins and protein modifications at subcellular resolution; with the availability of additional isotopes, measurement of over 100 markers will be possible. We applied imaging mass cytometry to human breast cancer samples, allowing delineation of cell subpopulations and cell-cell interactions and highlighting tumor heterogeneity. Imaging mass cytometry complements existing imaging approaches. It will enable basic studies of tissue heterogeneity and function and support the transition of medicine toward individualized molecularly targeted diagnosis and therapies.

Summary Toll‐like receptors (TLRs) are key receptors of the innate immune system and show cell subset‐specific expression. We investigated the messenger RNA (mRNA) expression of TLR genes in human haematopoietic stem cells (HSC), in naïve B cells, in memory B cells, in plasma cells from palatine tonsils and in plasma cells from peripheral blood. HSC and plasma cells showed unrestricted expression of TLR1–TLR9, in contrast to B cells which lacked TLR3, TLR4 and TLR8 but expressed mRNA of all other TLRs. We demonstrated, for the first time, that TLR triggering of terminally differentiated plasma cells augments immunoglobulin production. Thus, boosting the immediate antibody response by plasma cells upon pathogen recognition may point to a novel role of TLRs.

Authorship note: GH and JML are co-first authors. Conflict of interest: LB, GL, and DJS are coinventors on the patent Diagnostics for Membranous Nephropathy (US 8,507,215 B2) with royalty income through Boston University (LB and DJS) and CNRS (GL). LB reports a grant from Sanofi Genzyme and advisory board fees from Visterra and receives author royalty and peer review payments from UpToDate, Inc. relating to topic cards on the subject of membranous nephropathy. DJS reports a grant from Sanofi Genzyme; consulting and advisory board fees from Advance Medical, Pfizer, and Visterra; and royalty payments from UpToDate, Inc. relating to topic cards on the subject of membranous nephropathy.

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