When normal human cells, capable of repairing ultraviolet-induced lesions in their DNA, are incubated in the thymidine analog 5-bromodeoxyuridine after ultraviolet irradiation, the analog is incorporated into the repaired regions. When such repaired cells are subsequently irradiated with 313-nanometer radiation and placed in alkali, breaks appear in the DNA at sites of incorporation of 5bromodeoxyuridine, inducing a dramatic downward shift in the sedimentation constant of the DNA. Cells from patients with the disease xeroderma pigmentosum, which causes sensitivity to ultraviolet, are incapable or only minimally capable of repair; such cells incorporate little 5-bromodeoxyuridine into their DNA under these conditions and, upon 313-nanometer irradiation and sedimentation in alkali, exhibit only minor shifts in DNA sedimentation constants. When fibroblasts developed from biopsies of normal skin and of skin from patients with xeroderma pigmentosum, as well as cells cultured from midtrimester amniotic fluid, were assayed in this fashion unequivocal differences between normal and xeroderma pigmentosum cells were shown. Xeroderma pigmentosum heterozygotes are clearly distinguishable from homozygous mutants, and results are available 12 hours after irradiation.

Amniocentesis↗

PubMed1971

Characterization of immunoglobulin structures from the surface of chronic lymphocytic leukemia cells.

Chronic lymphocytic leukemia cells with relatively large amounts of mu and kappa immunoglobulin structures on the surface, and apparently very small amounts intracellularly, were subjected to homogenization or washing after freezing and thawing. After a light centrifugation, which sedimented the nuclei and unbroken cells, most of the immunoglobulin structures were found in the supernatant. Ultracentrifugation, which was performed to remove the membranes from the supernatant, sedimented only half the amount of the immunoglobulin structures. By sucrose density gradient ultracentrifugation and Sephadex G-200 filtration, the unsedimented immunoglobulin structures were shown to consist of 7S IgM and free kappa chains. About 80,000 7S IgM molecules were calculated to be present on each cell. The amount of kappa chains not associated with IgM was estimated to be equal to the amount of kappa chains in IgM. Inhibition of passive hemagglutination was used to detect and quantitate the immunoglobulin structures.

Aged↗

PubMed1971