Measuring antigen-specific immune responses -- What is different and what is better?

Extract: In the old days the "blood picture" was an important diagnostic tool in general medicine and in hematology, in particular. It is also referred to as blood film, full-blood count, or differential blood count in more modern terms. Today, rather than having a technician or a medical doctor looking at a microscopic slide, machines analyze the cellular composition of a small amount of peripheral blood and create an easy-to-read output for the physician. The information requested from such an examination today is of the same nature in principle as it was 25 years ago: a summary of the numbers, composition, and characteristic changes of blood cells, including red blood cells, platelets, and white blood cells. In immunology, there is a particular interest for white blood cells, because these represent an important part of the immune system. By looking through a microscope a trained technician can discriminate mainly three populations of white blood cells in an appropriately stained blood smear: granulocytes, lymphocytes and monocytes (in order of frequency). Mostly, changes in their composition or cellular deviations resulting in gross morphologic changes can be picked up this way. Modern cell analyzers, which are based on the principle of measuring cellular impedance, sometimes combined with optical parameters, by contrast, can reveal even smaller changes of red and white blood cells that would remain unnoticed in optical microscopy, and importantly, these measures are based on many more cells than can be evaluated on a blood film, increasing the reliability of the result.