Validation of the combined toxin-binding inhibition test for determination of neutralizing antibodies against tetanus and diphtheria toxins in a vaccine field study in Viet Nam.

Determination of seroconversion and measurement of protective antibody levels in children against vaccine components are essential for gauging and monitoring the efficacy of paediatric vaccination programmes. For this purpose, we assessed the combined toxin-binding inhibition (ToBI) test for determining neutralizing antibodies to tetanus and diphtheria in a diphtheria-pertussis-tetanus (DPT) vaccine field trial in Viet Nam. A simple procedure involving collection of blood samples on filter-paper was found to be a suitable alternative to collection by venepuncture, despite a reduction in the sensitivity of the ToBI test as a result of the step necessary to elute the antibodies from the filter-paper. The results obtained demonstrate that the ToBI test can feasibly be carried out under field conditions. Preliminary results obtained with the ToBI test in DPT field trials indicate that a fourth dose of DPT vaccine one year after the third dose should be considered by developing countries.

PIP: In Vietnam, health workers collected blood samples from adults working at the National Institute of Vaccines and Biological Substances in Nha Trang and Dalat and from healthy unvaccinated infants 3-9 months old from the district areas/provinces of Tien Giang and Lam Dong to assess the combined toxin-binding inhibition (ToBI) test for determining neutralizing antibodies to tetanus and diphtheria in a diphtheria-pertussis-tetanus (DPT) vaccine field trial. Researchers also aimed to validate the use of a simple filter-paper blood collection method. There was a necessary step to elute the antibodies from the filter-paper, which reduced the sensitivity of the ToBI test. Nevertheless, in the ToBI test, blood collected on filter-paper yielded similar antibody titer estimations as those obtained by venepuncture. The Biotek method to estimate antibody titers yielded higher correlation coefficients than the OD50 method: tetanus (0.998 vs. 0.98) and diphtheria (0.956 vs. 0.95). One month after the third injection, all the children had antitoxin titers greater than 0.06IU/ml. By one year after the third injection, only 45% had antitoxin titers greater than 0.06IU/ml for diphtheria while all still had antitoxin titer levels above this value for tetanus. This suggests that health providers should consider administering a fourth dose of DPT vaccine one year after the third dose. These findings indicate that the ToBI test can be conducted under field conditions.

Measurement of antigen specific lymphocyte proliferation using 5-bromo-deoxyuridine incorporation. An easy and low cost alternative to radioactive thymidine incorporation.

The classical in vitro assay for the determination of cell mediated immune responses is the lymphocyte transformation test (LTT) in which cell proliferation is measured by incorporation of radioactive labeled thymidine (3H-TdR). The LTT assay using 3H-TdR is less suited for modestly equipped laboratories as it is costly, laborious and involves the need to handle radioactive isotopes and specialized equipment. Here we describe an improved alternative LTT method which is capable of detecting specific cellular immune reactions (CMI) against (mycobacterial) antigens in vitro. This assay, the bromodeoxyuridine-ELISA LTT test, is simple, less expensive, reproducible and is as sensitive as the 3H-TdR test. The specific advantages of the test are a simple denaturation step and the fact that no radioactive isotopes are needed. The test is specifically suited for research laboratories in tropical countries which study CMI in those human infectious diseases where this arm of the immune response plays a pivotal role in the generation of immunity, e.g., in tuberculosis, leprosy and leishmaniasis.

Skin test responsiveness to a series of new tuberculins of children living in three Vietnamese cities.

A skin test survey was conducted among 1035 children aged 7-19 years living in three cities in Vietnam. Fifteen new tuberculins, including leprosin-A, were applied; an induration of 2 mm diameter or more was considered positive. Compared to some other tropical countries, low levels of sensitisation were recorded and remarkable regional differences were found. Positivity to any tuberculins (pooled data) among non-BCG-vaccinated children was significantly lower in Hanoi (13.1%) and HoChiMinh-City [HCMC] (15.5%) than in Nha Trang (25.7%) [p = 0.001 and p = 0.012, respectively]. The proportion of non-vaccinated children responding to Tuberculin ranged from 18.4% in Hanoi to 54.5% in Nha Trang. Leprosin-A elicited a response in 14.9% of the children in Nha Trang, but in very few of those in Hanoi (4.3%) or HCMC (3.0%). Thus, of the three cities studied, significant sensitisation to both M. tuberculosis and M. leprae was demonstrable only in Nha Trang. In Hanoi most of the response was to fast-growing species whilst in HCMC and Nha Trang it was mainly to slow-growing species. These results may account in part for the observed differences in the prevalence of tuberculosis and leprosy between the north and the south of Vietnam.

Investigation of bone and mineral metabolism in hyperthyroidism before and after treatment using calcitonin, 47Ca and balance studies.

Seventeen normocalcaemic patients with severe hyperthyroidism were examined before therapy was initiated; 9 were re-examined about 1 year later. Studies with 47Ca under balance conditions and with calcitonin demonstrated a high rate of bone resorption in untreated patients. As a result of the increased bone turnover, the reaction to 6 MRC units of porcine calcitonin iv was more marked in the untreated than in the treated patients or the control group. In contrast to the normal diurnal pattern for PO4, it was found that during fasting the plasma PO4 level increases in the morning in patients with hyperthyroidism. This increase which was not suppressed by the administered dose of calcitonin developed in spite of an elevated urinary PO4 excretion. After treatment, the serum Ca concentration as well as the urinary and faecal Ca excretion was decreased. The Ca balance improved; the rapidly-exchangeable Ca pool returned to normal. The slowly-exchangeable and the total Ca pools, however, remained enlarged. The rate of bone resorption normalized. The accretion rate on the other hand remained elevated. This is atributed to continued enhancement of bone formation to compensate for the previous loss of bony tissue.