In this issue

Understanding the Complexity of Stem Cell Signaling

When working with stem cells, functional flow cytometry is a very useful technique, as the Side Population (SP) can only be accurately identified based on the efflux of the fluorescent dye Hoechst 33342. SP cells are rare stem cells with expression of ABCG2, a membrane multidrug transporter from the ABC family. Although many ABC transporters have been identified as drug resistance proteins, they may play an additional role regulating the traffic of endogenous or other physiological substrates. Particularly, ABCB1 and ABCG2 transporters are highly conserved in normal stem cells, and may shield the stem compartment from the action of a series of ligands involved in signal transduction. In their current work, Balbuena and coworkers describe how the highly conserved Sonic Hedgehog (Hh) pathway can be modulated through the activity of ABCG2 in SP cells with stem-like properties. This upstream regulation of Hh signaling intermediate levels might preserve the stemness of the SP compartment.

In this issue: page 672

Pitfalls of Her2-Targeting

Integrated Her2 receptor targeting using combinations of therapeutic antibodies (Trastuzumab, Pertuzumab) and small molecule kinase inhibitors (Lapatinib) is a promising therapeutic approach for overcoming breast cancer cell resistance. Nevertheless treatment efficiency gets potentially undermined by ErbB-specific growth factors which affect the ErbB receptor activation upon induction of receptor interaction. The study by Diermeier-Daucher and coworkers demonstrates a profound extinction of the growth inhibitory effect caused by Lapatinib by the presence of the EGFR-specific epidermal growth factor or the Her3/4 receptor-specific growth factor Heregulin. While the compensatory effect of EGF on Lapatinib-induced cell cycle inhibition is reversed both by Trastuzumab and by Pertuzumab, the Heregulin-caused compensation of Lapatinib-related growth inhibition is only restored by Pertuzumab but not by Trastuzumab. Overall the study highlights the complex regulation of ErbB receptor interaction/activation. In order to optimize individual patient treatment the study challenges further preclinical and translational research addressing modular cell targeting.

In this issue: page 684

Routine Leukocyte Differential Count: Going with the Flowz

Differential counting of leukocytes in peripheral blood is frequently performed in clinical diagnostic laboratories even during evening and night services. Most samples are automatically analyzed by haematology analyzers, flagging aberrant samples for manual microscopic review. Microscopy has well known disadvantages such as significant statistical sample errors (only 100–200 counted cells) and inter-observer subjectivity. This problem may be solved using flow cytometry instead of microscopy, counting several ten-thousands of cells using a cocktail of well-defined antibodies for objective immunological definition, enabling identification of far more leukocyte subsets than feasible with microscopy or haematology analyzers. Several groups have reported single-tube antibody cocktails to perform leukocyte differentiation based on different flow cytometric strategies (Cytometry B 2010;78B:319–328; Cytometry A 2010;77A:552–563). In this issue, van de Geijn and coworkers report their Leukoflow assay that performs 5-color flow cytometric leukocyte differentiation into at least 13 populations including CD34+-blasts and plasma cells using 10 antibodies.

In this issue: page 694

Detection of Engineered Nanoparticles in Bacteria Using Flow Cytometry

Engineered nanoparticles (ENPs) can influence the scatter parameters of bacteria when bound on the cell surface and/or internalized. A new method was developed by Kumar and coworkers for rapid detection of ENP internalization in live bacteria for several generations under different experimental conditions using flow cytometry. Even though the ENPs tested (ZnO, TiO2) had similar optical properties, there was a marked difference in the positioning of treated bacteria in dot-plots. ENPs coated with cellular proteins exhibited an enhanced internalization as compared to bare nanoparticles. These observations were validated using transmission electron microscopy. This new method not only allows the detection of ENPs in bacteria but may also serve as a tool for environmental toxicologists to assess the safety/toxicity of ENPs used in consumer and therapeutic products, which ultimately come in contact with microbiomes.

In this issue: page 707