Featured Article
Friday November 13, 2009
by Catherine Shaffer
How many cells are in your sample? There are a number of different ways to answer that question, from manual counting through a microscope to sophisticated flow cytometry instrumentation. With cell number becoming relevant in more and more research and clinical applications, market trends now show a growing number of researchers looking for cell counting tools that are automated and tailored to their needs. These needs may range from extra features on a fluorescent microscope or computer imaging program to a top-of-the-line cell sorting flow cytometer.
Flow cytometry is the most powerful of the cell sorting options. Flow cytometers are very often coupled with a fluorescent detection system, and can count labeled cells in a stream flowing past the detector at a rate of up to thousands per second. Partec has been active in the field of flow cytometry since the founding of the company in 1967. They offer a complete package including instrumentation, reagents, and training, customized for the intended application. Partec's strategy is to provide a dedicated line of flow cytometry instruments that do only what the end user requires, without all of the bells and whistles of a high end flow cytometry system. This makes the instrument compact and affordable. Nevertheless, also multilaser, multiparameter systems for high end research are available from Partec.
Cell counting for HIV/AIDS, TB, and malaria monitoring are the major clinical applications served by Partec. They also provide a selection of customized instruments for custumers doing blood cell analysis in this space for counting CD4 cells, leukocytes or other immune system related subtypes of cells. Says Roland Göhde, Director of the Partec Essential Healthcare division, “We do nothing else but to precisely count these cells of interest without requiring any reference counting method as needed for most other conventional flow cytometers. Cell counting can therefore be quick, and very highly affordable.”
Automated microscopy is another approach that can streamline the cell counting process. Automated counting offers a number of benefits over manual cell counting. It has higher throughput, accomplishing in thirty seconds a task that would take ten minutes to perform by hand. It also gives better results with fewer mistakes such as miscounting cells, transcription errors, and mistakes in concentration calculations. It also eliminates user variability, which can crop up when different workers have slightly different counting styles.
According to Craig Weiss Vice President of Marketing of Nexcelom Biosciences, there's been a major shift in recent years in customers' willingness to adopt automated cell counting methods. “Several years ago, we really had to try to sell people on the concept,” says Weiss. “The analogy is that if you go back 20 or 25 years, nobody used Microsoft Excel. People had a calculator, a ruler, and a pencil. Now, everybody goes right to Excel.”
Nexcelom has taken automated cell counting one step further; their Cellometer Vision instrument couples brightfield and fluorescence microscopy with computerized image analysis. The user pipettes a 20 microliter sample into the counting chamber (which is similar to a microscope slide) and inserts it into the instrument, which then take an image of the slide and counts the total and fluorescent positive cells. Says Weiss, “It doesn't fully replace a flow cytometer. Our intent wasn't really to replace flow. Our intent was to complement it, so researchers could have a fast, simple method to count cells and quantify fluorescence for applications such as determining GFP transfection efficiency, and viability using propidium iodide. We wanted to make sure people are using the flow cytometer for assays that really need that power.”
In a sense, the Cellometer Vision bridges the gap between a fluorescent microscope and a fully-functioned flow cytometer. Some unique applications for the Cellometer include determining the concentration and viability of primary cells such as hepatocytes and adipoccytes. Hepatocytes are important in toxicology work. “Because of their morphology,” says Weiss, “No other automated technique can count and determine viability of primary hepatocytes.” The Cellometer also accurately counts and measures size of primary adipocytes, which are very fragile and quite difficult to distinguish visually and thus difficult to count using manual methods.
The increased availability of “in-between” tools like a small scale flow cytometer or an imaging-based automated cell counting system is good news for laboratories that do a lot of cell counting work. The difference between ten minutes and thirty seconds isn't much for something you do once a day, but when you multiply it by many times and many days, this can add up to a lot of time saved. As well, it frees up a fully functioned flow cytometer for jobs that can't be done any other way.