ANALYTICAL MAGNETAPHERESIS OF FERRITIN-LABELED LYMPHOCYTES

Analytical magnetapheresis is a technique for analyzing magnetic parti cles in suspension. The magnetically susceptible particles form a depo sition pattern from the suspending medium under carefully controlled f low and magnetic field conditions. This technique was used to determin e the effective magnetic volumetric susceptibility, Delta(chi), of hum an lymphocytes labeled with an iron-rich protein, ferritin. Dynabeads M450, monodisperse polymeric beads doped with magnetite, of a diameter 4.5 mu m, close to that of human lymphocytes, were used as a referenc e. The experiment showed an almost complete deposition of ferritin-lab eled lymphocytes at an average now velocity of 0.28 mm/s, a representa tive magnetic held of 1.67 T, and a magnetic field gradient of 2.57 T/ mm. The calculated Delta(chi) (2.92 +/- 0.24) x 10(-6)[SI] (ferritin-l abeled lymphocytes), and the corresponding number of ferritin molecule s per lymphocyte was (1.75 +/- 0.44) x 10(7). In comparison, an almost complete deposition of the Dynabeads was observed at a much higher av erage now velocity, 15 mm/s, a much lower field, 0.164 T, and a much l ower field gradient, 0.025 T/mm. These results corresponded to a much higher Delta(chi) = 0.245[SI] (Dynabeads M450). These results offer im portant guidelines in evaluating the use of ferritin as a soluble magn etic cell label.