Limitations in the quantitative separation of DNA samples by density gradient centrifugation.
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A method for the isolation of an enriched population (greater than 95%) of bovine polymorphonuclear leukocytes (PMNs) was developed using density gradient centrifugation. Leukocytes were isolated from peripheral blood by centrifugation in a density gradient medium (Percoll) of specific gravity 1.092. Viability was greater than or equal to 95% and the isolated PMNs were functional in migration inhibition and chemiluminescence assays. This has proved to be a simple effective method for obtaining bovine PMNs and yields cell populations that can be utilized for a variety of measures of PMN function.
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Human erythrocytes (RBC) from whole blood were separated according to their specific densities by centrifugation on a polyvinyl-pyrrolidine-coated colloidal silica matrix (Percoll) into four major subpopulations. By indirect immunofluorescence assay, the most dense RBC subpopulation, with specific density greater than 1.110 g/ml (3%-5% of total RBC), was positive for membrane-bound immunoglobulin; the remaining, less dense subpopulations were negative. IgG was present on 85%-95%, IgM on 28%-32%, and IgA on 15%-20% of the RBC in the most dense population. When these immunoglobulins were eluted, radiolabeled, and used in binding studies with autologous RBC fractions subjected to thermal and/or enzymatic treatment, they reacted specifically with the less dense RBC subpopulations. These results suggest that previously cryptic antigens were revealed by the activity of neuraminidase on the plasma membranes of the treated RBC.
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The conditions for the separation of rat high density lipoproteins (HDL) in a single ultracentrifuge run are described. By this method six serum samples can be processed simultaneously. HDL is separated into two main fractions, one with apolipoprotein E and the other with apolipoprotein A-I as the major protein component. The apolipoprotein E-rich HDL contains a relatively high amount of phospholipid and unesterified cholesterol and therefore resembles HDL-1 or apolipoprotein E HDL as isolated by other methods. The other HDL fraction resembles HDL-2. The two HDL fractions appeared to be heterogeneous with respect to apolipoprotein composition. The HDL-1 consisted of particles with and without a low percentage of apolipoprotein A-I. The HDL-2 consisted of particles with a variable amount of apolipoprotein E and A-IV. During incubation of rat serum for 5 h at 37 degrees C in the presence of dithiobis(2-nitrobenzoic acid) (DTNB) a small shift of the HDL-2 peak to lower densities occurred. Incubation of the serum without DTNB led to a loss of cholesterol from the 'light' HDL-1 fractions and an increase in cholesterol ester in fractions at densities intermediate between those of HDL-1 and HDL-2 and in fractions at the densest part of the gradient.
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