Isolation of two forms of decay-accelerating factor (DAF) from human urine

Stool decay-accelerating factor as a marker for monitoring the disease activity during leukocyte apheresis therapy in patients with refractory ulcerative colitis

BACKGROUND AND AIMS

We have shown previously that concentrations of stool decay-accelerating factor (DAF; CD55), a complement regulatory protein, in patients with ulcerative colitis (UC) are increased in relation to the severity of the colonic mucosal inflammation. In the present study, we evaluated the usefulness of stool DAF as a marker for monitoring disease activity in patients with steroid-resistant active UC being treated with leukocyte apheresis performed with a centrifugal cell separator.

METHODS

Twenty-one patients with active and steroid-resistant UC were treated with leukocyte apheresis once a week for 4 weeks, and stool DAF concentrations were determined weekly by immunoassay.

RESULTS

After treatment, 11 (52%) of the 21 UC patients went into remission. Stool DAF concentrations decreased promptly and steadily in the responsive group. The difference reached statistical significance as soon as after the second apheresis session (P < 0.003), compared with values before the therapy and corresponding values in the non-responsive group (P = 0.024). The reduction in stool DAF concentrations after the second apheresis session was significantly greater in the responsive group (median 90%, range 22-90%) than in the non-responsive group (median -13%, range -307-94%) (P = 0.008). Hematological tests, that is, white blood cell (WBC) count and C-reactive protein, declined significantly during the apheresis therapy, but not in relation to therapeutic response.

CONCLUSION

Stool DAF concentration is a useful marker in the clinical response of UC patients to treatment with leukocyte apheresis.

Testing of multiple samples increases the sensitivity of stool decay-accelerating factor test for the detection of colorectal cancer

OBJECTIVES

We previously reported that the measurements of stool decay-accelerating factor (DAF), a membrane-bound, complement regulatory protein, may be valuable for the detection of colorectal cancer. Recently we have refined the immunoassay for stool DAF. In the present study, using the refined assay, we measured stool DAF concentrations in multiple samples from patients with colorectal cancer and in healthy controls to determine whether testing of multiple samples would increase the sensitivity of the stool DAF test.

METHODS

DAF was measured in three spontaneously passed stool samples from each of 100 patients with colorectal cancer and 100 control subjects without apparent colorectal disease.

RESULTS

The stool DAF concentrations in the patients with colorectal cancer (median 11.1 ng/g stool; interquartile range 2.9-32.7 ng/g) were significantly higher than concentrations in the subjects without colorectal diseases (median 1.6 ng/g stool; interquartile range 0.4-3.4 ng/g) (p<0.0001). Testing of two samples from each patient significantly increased the sensitivity (72%) of the stool DAF test without significantly decreasing its specificity (92%). The stool DAF test was positive in more than one half of patients with colorectal cancer at a relatively early TNM stage or with negative fecal occult blood test.

CONCLUSIONS

These findings suggest that stool DAF is a marker of colorectal cancer independent of fecal occult blood and testing of two samples increases the sensitivity of the stool DAF test. Measurement of stool DAF now seems worthy of further consideration as a noninvasive method for the detection of colorectal cancer.

Distinct forms of DAF in urine and blood

DAF is a GPI-anchored protein expressed on all blood cells and most other cell types. This complement regulatory protein functions intrinsically in cell membranes to protect host cells from autologous complement attack. A soluble form is found in body fluids. In human urine, two forms of DAF have been described. Here we report that these two forms correspond to soluble DAF and to DAF bound onto urinary vesicles. With a newly established, highly sensitive ELISA, the proportion of these two forms could be quantified in healthy individuals and patients having renal disorders. This ELISA allowed us to measure DAF on blood cells and also in plasma. In contrast to urine, human plasma contained only soluble DAF when the plasma was thoroughly depleted of platelets. The concentration of soluble DAF in human serum was always lower than in the corresponding plasma, suggesting that this form might adhere to the clot during the coagulation process.

Decay-accelerating factor (DAF) in stool specimens as a marker of disease activity in patients with ulcerative colitis (UC)

Colonic epithelial cells of patients with UC express DAF in relation to the severity of mucosal inflammation. The aim of this study was to determine whether this factor in stool could be used as a marker of disease activity in UC patients. Stool DAF was measured by use of an immunoassay in 181 stool specimens obtained from 55 patients with UC of various levels of disease activity. Stool DAF concentrations in patients whose UC was active (0.0-785.6 ng/g stool; median 47.1 ng/g; n = 115) were significantly higher than concentrations in patients whose disease was inactive (0.0-48.6 ng/g; median 0.0 ng/g; n = 66) (P < 0.0001). Values in active UC patients also were higher than those in control patients with diarrhoea (0.0-30.0 ng/g; median 0.0 ng/g; n = 26) (P < 0.0001) and in control subjects without apparent colorectal disease (0-20.4 ng/g; median 0.0 ng/g; n = 44) (P < 0.0001). The elevated levels of stool DAF obtained from UC patients in relapse declined markedly in specimens collected after the disease went into remission following medical therapy. Stool DAF levels correlated with the severity of endoscopic and histological findings and the degree of DAF expression on the colonic epithelia. Our results suggest that the measurement of stool DAF is useful as a non-invasive means of monitoring intestinal disease activity in patients with UC.

Detection of decay-accelerating factor in stool specimens of patients with colorectal cancer

BACKGROUND & AIMS

Colorectal cancers have an increased expression of decay-accelerating factor (DAF). The aim of this study was to determine whether stool specimens of patients with colorectal cancer contain increased amounts of DAF.

METHODS

DAF was measured using an immunoassay in the stool specimens of 40 persons with colorectal cancer, 18 with colorectal adenomatous polyps, 13 with upper gastrointestinal cancer, and 41 without gastrointestinal disease.

RESULTS

Stool DAF concentrations in patients with colorectal cancer (0-9.8 ng/g stool; median, 1.6 ng/g) were significantly higher than those in patients with adenoma (0-6.4 ng/g; median, 0 ng/g) (P < 0.05), patients with upper gastrointestinal cancer (0-3.1 ng/g; median, 0 ng/g) (P < 0.05), and subjects without gastrointestinal disease (0-3.4 ng/g; median, 0 ng/g) (P < 0.01). Resection of colorectal cancers caused a marked decrease in stool DAF concentrations. The stool DAF test was positive in a substantial portion of patients with colorectal cancer whose tumors were small ( < 2 cm), at an early TNM stage, or unassociated with fecal occult blood positivity. The sensitivity of the test for colorectal cancer was 55%, and the specificity was 85%.

CONCLUSIONS

The measurement of stood DAF deserves evaluation as a test for detection of colorectal cancer.

Complete determination of disulfide bonds localized within the short consensus repeat units of decay accelerating factor (CD55 antigen)

Decay accelerating factor (DAF) has 4 SCR (short consensus repeat) units. Each SCR unit consists of approx. 60 amino acids characterized by having four conserved cysteine residues and several other highly conserved residues which include proline, tryptophan, tyrosine/phenylalanine and glycine. To determine the disulfide-bonding pattern, we used the urine form of DAF. After thermolysin and trypsin digestion, we isolated seven disulfide-linked peptides by HPLC purification. Because all of the cysteine residues are disulfide-bonded, DAF should contain eight disulfide bonds. After subtilisin and trypsin digestion, we isolated the eighth disulfide-bonded peptides by HPLC purification. From sequence analyses of these peptides, we could identify all disulfide bonds in the 4 SCR units of DAF as being between the first and the third and between the second and the fourth half-cystines within each SCR unit.