DNA binding to human leukocytes. Evidence for a receptor-mediated association, internalization, and degradation of DNA.

Previous studies have indicated that white blood cells possess DNA on their outer membranes. In this study we set out to determine whether exogenous DNA bound to cells in a fashion compatible with a ligand receptor union. Purified populations of white blood cells; neutrophils (polymorphonuclear leukocytes, PMN), adherent mononuclear cells (ADMC), rosetting lymphocytes (E+ cells), and nonrosetting lymphocytes (E- cells) were incubated with radiolabeled lambda phage DNA in increasing concentrations. Binding of [3H]DNA was a saturable process and was inhibited by excess cold DNA and prior trypsinization of the cells. Rate zonal density centrifugation of purified cell membrane preparations confirmed that DNA was binding to the outer cell surface. The dissociation constant for all four cell types was approximately 10(-9) M, and from 0.81 X 10(3) to 2.6 X 10(3) molecules of lambda phage DNA bound to each cell depending upon cell type. Binding was not competitively inhibited by RNA, polydeoxyadenylic acid-polydeoxythymidylic acid (poly [d(A).d(T)]), or mononucleotides. Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE)-separated proteins from PMN, ADMC, E+, and E- cells were electrophoretically blotted onto nitrocellulose sheets; a probe of biotin-labeled DNA indicated a single species of DNA-binding molecule migrating in a position consistent with a molecular weight of 30,000. Isotopic and immunofluorescent studies indicate that DNA is internalized and degraded to oligonucleotides; this process is inhibited by cycloheximide. These results support the notion that there is a common binding site for DNA on white blood cells, that the stoichiometry of the association is compatible with a ligand receptor relationship, and that this apparent receptor is responsible for the endocytosis and degradation of exogenous DNA.

Angiographic findings in mixed connective tissue disease. Correlation with fingernail capillary photomicroscopy and digital photoplethysmography findings.

Thirteen patients with mixed connective tissue disease underwent hand angiography to assess the degree of vascular abnormalities and their correlation to nailfold capillary microscopy and digital photoplethysmography findings. Organic obstruction was found in 60% of ulnar arteries, 87% of superficial arches, 13% of deep arches, and 65% of digital arteries. Fingernail capillary abnormalities were seen in 90% of patients. Normal photoplethysmography results had a predictive value of 91% for identifying digits without bilateral occlusions. These findings indicate a hitherto unrecognized propensity for disease of both small and medium-sized vessels in patients with mixed connective tissue disease.