Journal of Leukocyte Biology 35: 19-30 (1984) Noninvasive Studies of Kupffer Cells In Situ by Magnetometry Peter Gehr, Joseph D. Brain, and Steven B. Bloom Respiratory Biology Program, Department of Environmental Science and Physiology, Harvard School of Public Health, Boston Magnetic iron oxide (gamma-Fe20 3) particles were injected intravenously into four male New Zealand white rabbits. Most of these particles were phagocy- tized by the Kupffer cells. When the animal was placed in a magnetic field , the particles in the liver became magnetized and aligned. After removal of the external magnetizing field, the particles collectively produced a remanent magnetic field which was measured at the body surface. The strength of this field was proportional to the amount of magnetic particles present in the liver; sequential measurements thus allowed us to describe their disappearance from the liver. After each magnetization, the remanent field rapidly decayed due to particle rotation (relaxation) . Since the particles were confined in pha- gosomes or secondary Iysosomes we conclude that movements of these organelles due to cytoplasmic motion caused relaxation. Magnetic particles might th erefore serve as probes for cytoplasmic motility of Kupffer cells in situ . Key words : Kupffer cells , magnetometry , cell motility , clearance INTRODUC TIO N 1 ron oxide particl es have been wid ely used to study th e char ac teri sti cs of ph agocytic ce ll s [3,24,28]. Th ese particl es are biologi ca ll y innocuous [1 9] and ca n be easil y visuali zed in li ght and el ec tron mi croscopes. Mi crogram quantiti es of mag netic iron oxide ca n be detec ted nonin vas ively with a tlu xgate [1 ,2,12, 13] or superconducting quantum interf erence mag netometer [6,7,8, 9] . Several inves tigators have used mag netic particl es to es timate cytoplasmi c vi scos ity of cell s in v itro [11 , 16 , 17 ,3 1] . Th e for ce needed to rotate th ese particl es with an el ec tromagnetic fi eld wa s used to es tim ate the vi scos ity. Previous studi es showed that when mag netic iron oxide particl es are inhaled th ey are rapidly inges ted by mac roph ages in th e air ways and alveo li [24] . Th ese Rccc iv cd June 24. 1983. Pctcr Gehr" s curre nt address is AnalOl1li sc hes In stitul. Uni vc rsi tat Bc rn . Pos t fa cil 1 39 CH-3000 Be rn 9. Swi tze rland (fo r reprint reques ts). © 1984 Alan R. Liss, Inc.