Cell tracking 2007: a proliferation of probes and applications.

The articles in this thematic issue, entitled "Tracking Cell Proliferation and Function," illustrate some of the choices made by authors pushing the envelope for cell tracking applications in their areas of interest. Over the past decade there has been a proliferation in the range of commercially available probes for these studies, the capabilities of the instrumentation used to detect them, and in the biological systems being studied. This introductory to the thematic issue presents the advantages and limitations of the more commonly used probes such as CFSE and PKH26, as well as emerging probes that expand the range of fluorescence available, including quantum dots and the new CellVue dyes. Appropriate method and instrument setup controls and possible data analysis strategies are discussed with the goal of urging experienced investigators to include all critical information and controls when publishing their data and of aiding researchers new to cell tracking to make informed decisions on which cell tracking reagent(s) are best suited for their particular application. All cell tracking assays have the common goal of determining the fate of a particular cell population within a heterogeneous environment, whether in vivo or in vitro. Some of the common themes among the contributions found in this issue include how various probes are used to track (i) cell proliferation, (ii) regulatory and effector immune cell function and (iii) membrane transfer and antigen presentation. Although these represent only a small fraction of the large and growing list of applications for cell tracking, clearly illustrate the growing trend toward the use of multiple tracking reagents and multiple detection modalities to address complex biological questions.