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Biomedical subjects

F Hoekstra

Publications and source records attributed to F Hoekstra.

9 recordsLinked to original sources
PubMed2005

Determinants of Dutch parents' decisions to vaccinate their child.

This study examines the factors that influence parents' decisions to have their children vaccinated under the Dutch National Immunisation Programme. A computer questionnaire was sent to 500 parents in 1999 (the response rate was 98.2%). The intention to vaccinate was most strongly determined by attitudes. The belief that vaccination is safe and the best way to protect children against infectious diseases positively influenced parents' attitudes. The idea that children receive too many vaccines simultaneously and that vaccination interferes with natural development had a negative effect on attitudes. Dutch parents believe that doctors only inform them about the benefits of vaccination and disregard possible drawbacks. Since attitudes did not appear to be the result of thorough deliberation, parents could easily be influenced by negative publicity about vaccination. Educational campaigns and practitioners' advice should provide complete information about all aspects of the question, enabling parents to make well-considered and therefore enduring decisions.

Adult↗
PubMed1997

Donor-specific anti-human leukocyte antigen class I antibodies after implantation of cardiac valve allografts.

The allospecific humoral immune response was examined in 31 patients in the first year after implantation of cryopreserved human cardiac valves. We determined the percentage antibodies against human leucocyte antigens (HLA) class I in a complement-dependent microlymphocytotoxicity test against a panel of 50 selected donors carrying most of the defined HLA-A and HLA-B specificities (panel-reactive antibodies). In blood samples taken immediately before implantation, no antibodies could be detected. Thereafter, antibodies were present in 23 of 31 (74%) patients (median panel-reactive antibodies: 57%, range 9% to 91%). In 21 patients the HLA-type of the valve donor was available. In four patients no blood samples taken after 4 weeks were available. In 14 of 17 patients (82%) with a follow-up of more than 1 month antibodies were present, and in 12 of these 14 (86%) antibodies were specifically directed against HLA class I of the donor. In conclusion, the formation of donor-specific antibodies is frequently observed after human cardiac valve replacement. It could be one of the factors leading to valve destruction and dysfunction.

Adolescent↗
PubMed1996

Donor-specific cellular immune response against human cardiac valve allografts.

We studied the presence of donor-specific T lymphocytes in explanted human cardiac valve allografts in vivo. From five of seven explants we propagated lymphocyte cultures in an interleukin-2 conditioned medium. Phenotyping revealed the presence of T-cell receptors in more than 95% of the lymphocytes obtained in each culture. Donor-specific cytotoxicity was demonstrated in three patients with known HLA status of the donor. Cytotoxicity was directed against only HLA class I in one patient, and against class I and/or class II in the others. These results indicate that donor-specific cellular reactivity can be induced by transplantation of human cardiac valve allografts.

Adult↗
PubMed1995

Stimulation of immune-competent cells in vitro by human cardiac valve-derived endothelial cells.

Both fresh and cryopreserved human cardiac valve allografts are transplanted without matching donor and recipient for blood group or human leukocyte antigens (HLA) and without the usual immunosuppressive therapy that follows organ transplantation. Calcification occurs in almost all transplanted valves, and in children acute valve failure is frequently seen. We hypothesized that failure of the human valve allografts could have an immunologic basis. This hypothesis was tested in a functional way by performing lymphocyte stimulation assays using fresh and cryopreserved valve pieces and endothelial cells derived from valve leaflets as stimulator. Human peripheral blood lymphocytes, both matched and mismatched for HLA antigens, were used as responder cells. The results were expressed as the stimulation index. Fresh valve pieces induced a significantly higher stimulation index (median, 9; range, 4 to 117) compared with the cryopreserved pieces (median, 2; range, 0 to 9; p = 0.002 by Wilcoxon test). The stimulation index was significantly reduced when lymphocytes matched for HLA-DR with the valve pieces were used (median, 1; range, 0 to 5) as compared with the HLA-DR-mismatched combination (median, 4; range, 2 to 117; p = 0.006, Wilcoxon test). Valve leaflet-derived endothelial cells were able to induce a median stimulation index of 8 (range, 3 to 15) when incubated with lymphocytes mismatched for HLA-A, -B, and -DR. In conclusion, stimulation of immune-competent cells in vitro is induced by both fresh and cryopreserved human valve pieces and by endothelial cells derived from fresh valve leaflets. The immune response can be reduced by using cryopreserved valves or by matching valve donor and responder lymphocytes for HLA-DR.(ABSTRACT TRUNCATED AT 250 WORDS)

Aortic Valve↗
PubMed1993

Postoperative local radiotherapy in rectal cancer: treatment results with limited radiation fields.

PURPOSE: The purpose of this study is to determine the treatment results and complication rates of postoperative local radiotherapy, with doses per fraction of 2.25 to 2.50 Gy, in patients with rectal carcinoma who have received macroscopically radical surgery. METHODS AND MATERIALS: A retrospective analysis was done of the records of all consecutive patients (N = 147) with rectal carcinoma Dukes' Stage B or C who have received postoperative local radiotherapy in our institution in the years 1981 through 1989. All patients have been treated on a limited target area covered by only local radiation fields. Locoregional fields covering the whole iliac node chains have not been given. In our treatment protocol doses per fraction were from 2.25 to 2.50 Gy and total doses from 50 to 55 Gy. The minimum follow-up was 24 months; eight patients have been lost to follow-up. RESULTS: The overall 5-year survival rate for the whole group of patients was 39%. The actuarial 2- and 5-year pelvic recurrence rates were 14% and 22% respectively for Dukes' B patients and 30% and 38% respectively for Dukes' C patients. The difference between the pelvic recurrence rates of Stage B and Stage C patients was statistically significant (p = 0.009). No other factors with prognostic significance for pelvic recurrence were found. The interval between surgery and radiotherapy especially had no influence on pelvic recurrence rates. The 35 pelvic recurrences were classified as follows: 17 in-field, 5 marginal, 1 out-of-field, and 9 peritoneal seeding; in three patients there was not enough information for classification. Of the 32 classified pelvic recurrences, the five marginal recurrences were probably geographical misses, only the one out-of-field recurrences, the five marginal recurrences were probably geographical misses; only the one out-of-field recurrence might have been prevented with locoregional radiotherapy. Serious complications caused by the radiotherapy have occurred in 3% of the patients. CONCLUSION: We conclude that the results of postoperative local radiotherapy alone are comparable with the published results of locoregional radiation. Even when relatively high doses per fraction are given low complication rates are seen.

Adenocarcinoma↗
PubMed1987

Radiation appendicitis: demonstration with graded compression US.

In a patient who had received presurgical radiation therapy for extensive rectal carcinoma, ultrasonography with graded compression disclosed an inflamed appendix. The patient had no clinical signs of acute appendicitis. At laparotomy for resection of the rectal carcinoma, the appendix appeared grossly abnormal and was removed. Pathologic examination showed severe radiation enteritis of the appendix. The sonographic appearance of radiation appendicitis closely resembled that of acute appendicitis.

Adult↗
PubMed1978

Dose response in radiotherapy for glottic carcinoma.

All consecutive patients with glottic squamous cell carcinoma treated primarily by radiotherapy from 1965 through 1974 have been analyzed to reveal response of the primary tumor in relation to the dose. This study appears to indicate presence of dose response for all stages of the primary lesions (T) of the glottic carcinoma except for the smallest ones namely TIS, T1a and T1b. The total number of advanced tumors is small and selected. But they tend to indicate presence of dose response. Out of 15 selected patients with T3 and T4 glottic tumors, 5 (33%) had attained local control by primary radiotherapy; two had distant metastasis at onset of therapy, while 5 (33%) needed salvage surgery for control of the residual or recurrent disease. The ultimate success rate is 66% (10 out of 15) for the patients with advanced tumors treated with a conservative approach. An ongoing study indicates similar, if not better preliminary results with high dose radiotherapy.

Adult↗
PubMedDate not supplied

Effect of cryopreservation and HLA-DR matching on the cellular immunogenicity of human cardiac valve allografts.

The cellular immunogenicity of fresh and cryopreserved human cardiac valve leaflets was measured in a lymphocyte proliferation assay. One fresh leaflet and a cryopreserved leaflet derived from the same valve were cut into 2 mm diameter pieces and incubated with responder peripheral blood mononuclear cells, matched or mismatched for HLA-DR. The tritiated thymidine incorporation into the lymphocytes measured after 7 days, was expressed as stimulation index. Fresh, HLA-mismatched valve pieces induced high stimulation index in all cases (median 9, range 4 to 117). The cryopreservation procedure resulted in a significantly lower stimulation index (p = 0.002, Wilcoxon), with a median stimulation index of 2 (range 0 to 9). In the instances where HLA-DR matched combinations were studied, cryopreservation was also associated with lower stimulation index. HLA matching itself was able to reduce the stimulation index both with cryopreserved and fresh valve pieces as stimulator, resulting in a median stimulation index of 4 (range 2 to 117) for the HLA-DR-mismatched and 1 (range 0 to 5) for the matched lymphocytes (p = 0.006, Wilcoxon). In conclusion, human cardiac valves are able to stimulate immune competent cells in vitro, even after cryopreservation. The cellular allogeneic response in vitro could be an explanation for valve allograft degeneration observed in the clinic. Matching for HLA-DR may reduce these effects.

Cryopreservation↗