A NEW TECHNIQUE FOR HIGH-RESOLUTION DENSITY GRADIENT-SEPARATION OF BONE-MARROW CELLS*

A method for separation and purification of mouse splenocytes by density gradient centrifugation

Spleen is an information-rich and easy-accessible peripheral lymphoid organ. It has complex cell composition because of the immunocytes maturity and settle down. Changes of the composition and function of these immunocytes are critical to body immune response. To understand the cell behaviors, specific cell subpopulations are required to be separated without heterogeneity. Density gradient centrifugation is one of the cell separation methods with high throughput. However, the greatest defect of this method is its low cell purity. In this study, the separation conditions of tumor-bearing mouse splenocytes were optimized by separation solutions with different density gradients. After separation, lymphocytes were located at the second layer with the proportion of 84.9%, monocytic-like myeloid-derived suppressor cells (Mo-MDSCs) were located at the fourth layer with the proportion of 54.2% and polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) were located at the sixth layer with the proportion of 85.5%. Cells in different layers were further determined by verifying the gene expression pattern of some chemokine receptors on cell surfaces. Furthermore, this method was also used to separate healthy mouse splenocytes. Therefore, this method will be highly useful to separate mouse splenocytes and has laid a foundation for further research on the changes and roles of immunocytes during the development of cancer.

The Lattice Boltzmann method and computational analysis of bone dynamics-I

Bone is comprised of an enormously hierarchical construction that promotes transportation of necessary fluids and solids, guaranteeing accurate function and growth. Bone remodeling is a combined process of bone creation and destruction. A number of mathematical models have been developed for the balanced and imbalanced bone remodeling. A brief overview regarding mathematical modeling of bone remodeling is provided. The Lattice Boltzmann method (LBM) has widely been implemented in CFD simulations, and it is becoming more suitable in the application of image processing amongst several others. Mainly, the LBM simulates the communication between synthetic particles dispersed in a lattice. Canaliculi and tortuous channels that have more or less roughly circular structure link among oval bodies identified as lacunae, and are vital to the function of bone. As there is a lack of equipment to inspect flow in channels on the order of measure of canaliculi, so the use of computational methods are more advantageous to give perceptivities into the nature of the flows. In this article, the computational fluid dynamics analysis is descried, using the Lattice Boltzmann method, to examine the result of the microscopic surface roughness of the canalicular wall, which is formed by collagen fibrils, on the flow profiles in the pericellular space.

Cellular events in the immune response : analysis and in vitro response of mouse spleen cell populations separated by differential flotation in albumin gradients

Cell suspensions from the spleens of normal mice or mice injected with sheep erythrocytes were separated on a discontinous bovine serum albumin density gradient. Four bands or subpopulations were obtained and were assayed for antibody-forming cells, and for antigen-sensitive precursor cells. The antibody-forming cells were assayed by the hemolytic plaque assay and the antigen-sensitive precursors were assayed by the number of plaque-forming cells which developed after 3 or 5 day's culture with antigen. It was found that both antibody-forming cells and their precursors were present in the denser region of the gradient when spleen cell suspensions were taken from unimmunized mice. In contrast, both antibody-forming cells and precursors floated to the top in cell suspensions from mice sacrificed 1, 2, or 3 days after antigen injection. The change in density was detectable as early as 12 hr and was complete by 18 hr. The cell which changed in density was specific for the antigen that brought about that change. The significance of these findings is discussed.

Application of some droplet sedimentation theories to layered erythrocyte suspensions

The applicability of some existing droplet sedimentation theories to erythrocyte suspensions was investigated using glutaraldehyde-fixed erythrocytes from horse, canine, pig, chicken, and human. The Svensson criteria were shown to underestimate the load supportable by a density gradient. The available theories on droplet formation times could not predict each other, and the data on erythrocyte suspensions, especially at high suspension concentrations. It was finally argued that, since the behavior of erythrocytes was not controlled by the diffusion process, the erythrocyte suspensions were not expected to exhibit lasting or absolute stability even when the particle load was small.

Separation of ovine oligodendrocytes into two distinct bands on a linear sucrose gradient

A new method for isolation of oligodendrocytes is described. The method was developed to isolate intact, viable cells and to fractionate oligodendrocyte subgroups. Finely minced ovine white matter (WM) is incubated in 0.1% trypsin at 37 degrees C for 3.6 min/g WM. Trypsin inhibitor is added to arrest the action of trypsin. Further disruption of tissue is achieved by passage through a series of screens (350 micrometer down to 30 micrometer pore size) and the crude suspension in 0.9 M sucrose is centrifuged at 2100 rpm (850 g) for 10 min. During this step myelin floats to the top of the tube while the cells form a pellet. The pellet is resuspended in 3-4 ml of 0.9 sucrose and applied to a linear sucrose gradient (1.0-1.2 M), which is then centrifuged at 1200 rpm (277 grams) for 40 min. Oligodendrocytes separate into two distinct bands on this gradient suggesting that two subpopulations have been isolated. There are small differences in size between cells from these bands. Oligodendrocytes isolated by this procedure remain viable and differentiated for months as evidenced by their ability to incorporate labeled precursors into galactocerebrosides and sulfatides and to synthesize myelin basic protein.

Separation of functional subpopulations of murine and human lymphoid cells on colloidal silica density gradients. I. Preparation of the Ludox AM gradient material and characterization of separation capacities

This report describes a unique modification of an isopycnic density gradient system utilizing as a separating menstrum colloidal silica (Ludox AM). The primary advantages of this preparation are: (1) It is chemically defined, allowing extremely reproducible cell separation employing different lots of material; (2) the physical parameters (pH, density, salt concentration) of the final gradient suspension can be manipulated over a wide range of values, allowing for the separation of many different biological materials; (3) it allows separation of very large numbers of lymphoid cells with greater than 95% recovery of applied cells; (4) separated cellular subpopulations can be easily washed free of silica and cellular function is retained. This paper is a report of the preparation and functional characteristics of the gradient material as it relates to the separation of very large numbers of lymphoid cell subpopulations in both mouse and man. Subpopulations of murine and human lymphocytes separated by this gradient material were assayed for IgM synthesis, T-cell mediated cytotoxicity, and lymphokine production.

Enrichment of PHA transformed lymphocytes in samples containing mixed populations

A dextran density gradient centrifugation method has been used to separate PHA transformed lymphocytes from nontransformed lymphocytes obtained from rat blood. Fifty-four percent of the transformed lymphocytes were recovered in the fraction at a density of 1.0620 g/ml. Eighty-five percent of the cells in this fraction were transformed cells while the remainder were non-transformed lymphocytes.

A diffusion driven instability in systems that separate particles by velocity sedimentation

Velocity sedimentation has been used extensively to separate particles according to the magnitude of their sedimentation velocity in suitable media. This technique has been used over a wide range of particle size from protein molecules, viruses, subcellular particles to whole cells. Successful separation demands that collective particle motion should not occur. In practice it is observed that such systems may, under certain circumstances, suffer from a particular type of instability which destroys the normal dependence of sedimentation velocity on particle size and density. The aim of this paper is to identify the critical parameters that determine the development of this instability. Stability criteria are deduced and predictions of the theory compared with published observations. Satisfactory agreement between theory and observation is obtained. It is concluded that the simple stability criterion, namely that stable sedimentation will occur if the total density gradient is in the direction of the sedimenting force, grossly overestimates the particle load that can be separated in practice. Some specific recommendations for optimum particle loading are included. Earlier theoretical and experimental works are briefly reviewed.