Methods in laboratory investigation. Isolation of guinea pig monocytes and Kurloff cells: characterization of monocyte subsets by morphology, cytochemistry, and adherence.

Guinea pig mononuclear cells were separated from peripheral blood using high-density Ficoll-Hypaque, following which the monocytes and Kurloff cells were isolated using counterflow centrifugation elutriation and Percoll gradient centrifugation. Monocytes were obtained in four counterflow centrifugation elutriation fractions. Small monocytes (283 micron3) constituted 33% of all monocytes and were acid phosphatase negative, nonadherent cells with a scant cytoplasm but characteristic reniform nucleus. Although present in low purity after counterflow centrifugation elutriation, they were enriched using Percoll gradients to 35%. Large monocytes (317 micron3) comprised 41% of all monocytes and were obtained in 81% purity by counterflow centrifugation elutriation. They were adherent cells positive for acid phosphatase and nonspecific esterase. Peroxidase-positive cells constituted 41 and 33% of the small and large monocytes, respectively. Intermediate-sized monocytes (300 micron3) comprised a mixture of monocytes with characteristics of both small and large monocytes. Very large monocytes (354 micron3) were peroxidase-negative, strongly adherent cells with a distinctive morphology characterized by a spherical nucleus and highly vacuolated cytoplasm. They comprised 7% of the total monocytes and are a heretofore unrecognized cell type in the circulation. These procedures also isolated Kurloff cells in high purity and yield. Kurloff cells are distinct to the guinea pig and were nonadherent cells that did not stain for acid phosphatase, peroxidase, or nonspecific esterase. This is the first report of the successful isolation of Kurloff cells as well as monocytes other than human into fractions that differ in size and function.