[Study of diphtheria anatoxins in immunochemical and tissue culture assays]

Equine diphtheria antitoxins from different manufacturers were studied. Their immunochemical interaction with diphtheria toxin, toxoid, and antigens of Corynebacterium diphtheriae in ELISA and immunoblotting assays as well as biological activity in CHO cell assay were compared. The discovered differences between antitoxin samples with stated equal activity in IU/ml point to heterogeneity of antigen composition in preparations used for immunization. Mentioned methods allow to standardize antitoxins basing on their biological activity and immunochemical characteristics.

Immunity against diphtheria and tetanus in German blood donors

After the recent diphtheria epidemics in Eastern Europe in the early 1990s, we re-evaluated the diphtheria and tetanus immunity of 321 German blood donors (192 men and 129 women). The mean antitoxin levels of all blood donors in this study, measured by commercial ELISA, revealed a questionable protection (0.1-1.0 IU/ml) against diphtheria. In 1994, 66.4% were without immunity against diphtheria (55.0% in 1997/98), 32.1% (41.5% in 1997/98) showed questionable protection and only 1.5% (3.5% in 1997/98) had protective antitoxin levels. The evaluation of tetanus immunity revealed only 0.5% (1.1% in 1997/98) of the subjects with no protection and 9.1% (8.5% in 1997/98) with questionable protection. For this reason, we conclude that the diphtheria epidemics only lead to an insufficient improvement of the immunization status in a healthy German population.

[The study of a specific activity of a new allogenic antidiphterial immunoglobulin]

A comparative investigation was conducted of several methods for measuring the activity of the diphterial antitoxin in the preparation of allogenic antidiphterial immunoglobulin. The results of the studies made allow recommending the flocculation reaction and statistical method for use at blood transfusion stations in Ukraine when manufacturing the antidiphterial immunoglobulin, due to their informative, economic value and because they can easily be performed.

Epidemiology of three cases of severe diphtheria in Finnish patients with low antitoxin antibody levels

During the 1990-1998 diphtheria epidemic in the newly independent states of the former Soviet Union, more than 150,000 infections and 5,000 deaths occurred. During this period, more than 10 million trips were made from Finland to Russia or vice versa. This resulted in only 10 cases of diphtheria in Finland. There was no secondary spread to healthcare workers or other close contacts. Three patients had severe respiratory tract diphtheria. All three were middle-aged men who had made a short visit to Russia, during which time they had intimate contact with local women. These findings suggest diphtheria was transmitted mainly by direct saliva contact. All patients with severe diphtheria had a non-protective level of antitoxin antibodies during the first days of the disease. Only the patient whose antibody titre rose rapidly to a protective level (>1 IU/ml) had an uncomplicated recovery. The other two, one of whom died, had myocarditis and severe polyneuropathy.

Immunity to diphtheria in Izmir, Turkey

In order to assess immunity to diphtheria in Izmir, Turkey, a total of 743 persons 1-70 years of age were selected with cluster sampling. The information on socio-demographic characteristics, vaccination status and diphtheria history was gathered for each participant. Diphtheria antitoxin levels were measured qualitatively by using micro-enzyme immune assay. Of studied population, 79.1% had fully protective antitoxin levels (> or = 0.1 IU/ml). Diphtheria protection rates showed a gradual age-related decrease, reaching minimum in the 30-44 age group, in which 40.2% of these subjects had antibody titre below the full protective level. The diphtheria antitoxin geometric mean titer was highest in the 5-9 year age group (1.05 IU/ml). Then, geometric mean titer decreased with increasing age, and reached the minimum level in the 30-44 age group (0.19 IU/ml). These results suggest that in Izmir, Turkey, full serological protection against diphtheria is only detectable in 60% of the adult population. The enhancement of diphtheria immunity by booster vaccinations in adolescents and adults should be considered in Turkey.

European sero-epidemiology network: standardisation of the results of diphtheria antitoxin assays

A European Sero-Epidemiological Network (ESEN) was established with the aim to co-ordinate and harmonise serological surveillance of immunity to communicable diseases in Europe. In this study the inter-laboratory standardisation of diphtheria toxin antibody measurements is reported. A standard panel of 162 sera was tested by the participating laboratories using an in vitro assay of their choice: VERO cell toxin neutralisation assay (NT), double-antigen delayed time-resolved fluorescence immuno-assay (DA-DELFIA), double-antigen enzyme-linked immunosorbent assay (DAE), toxin binding inhibition test (ToBI) and an indirect enzyme-linked immunosorbent assay (ELISA). The results were standardised using regression against the NT. The variations due to inter-laboratory and inter-assay variation, which would otherwise make it difficult directly to compare the main serum bank results by the different laboratories and the various assays were successfully minimised by the standardisation. The regression equations obtained will be used to transform the respective local results of testing the main serum bank into the reference test unitages. This study also gave the opportunity to compare the various assays within and between laboratories. This demonstrated a very high correlation between DA-DELFIA, DAE, ToBI and the NT. The ELISA showed a good correlation, too, however sera below some 0.1 IU/ml were overestimated.

Evaluation of single- and dual antigen delayed fluorescence immunoassay in comparison to an ELISA and the in vivo toxin neutralisation test for detection of diphtheria toxin antibodies

An evaluation of the delayed fluorescence immunoassay (Delfia) against an ELISA method for determination of diphtheria antitoxin levels in serum was performed. The Delfia was also validated in the in vivo toxin neutralisation test (Txn) in rabbits. Two variants of the Delfia were studied, a single-antigen Delfia (sDelfia) with only the diphtheria toxin included and a dual-antigen Delfia (dDelfia) with tetanus toxoid included for simultaneous detection of antibodies against two antigens. The diphtheria antitoxin cut-off levels in the sDelfia and the dDelfia were 0.004 and 0.002 AU/ml, respectively, which is lower than the internationally accepted level showing any protection against diphtheria (0.01 IU/ml). Both Delfia variants showed good correlation with the ELISA procedure above the ELISA cut-off level of 0.02 AU/ml. Results from samples assayed in the in vivo Txn assay indicated that the low antitoxin levels detected by the Delfia were valid. These results show that the Delfia could be considered as an in vitro reference method for detection of diphtheria antitoxin in seroepidemiological surveys and vaccine studies.

Improved ELISA for determination of anti-diphtheria and/or anti-tetanus antitoxin antibodies in sera

Double-antigen ELISAs for detection and quantification of anti-tetanus or anti-diphtheria antibodies in serum have been developed. The assays showed good correlations with established toxin neutralizing assays and were functionally specific for IgG antibodies. The double-antigen set-up allows specific antibodies to bind to antigen-coated microtitre wells with one arm and the free arm to bind to biotin-labelled antigen. The amount of antibodies able to bind labelled antigen was assessed by adding enzyme-conjugated streptavidin and colour substrate followed by measurement of the colour using an ELISA reader. The double-antigen principle makes it possible to compare samples of different species on the same plate, permitting the direct use of existing international references of animal or human origin. The double-antigen ELISAs showed a detection limit of 0.00002 IU/ml for both antibodies and were suitable for quantifying antibodies in blood samples collected on filter paper as well as in serum. The assays required no special equipment compared to traditional ELISA.

Diphtheria immunity in Flanders

A serological survey to determine the immunity to diphtheria in the Flemish population was conducted according to the recommendations of the World Health Organization. Immunity to diphtheria was determined on a randomised, stratified sample (1679 serum samples) from an existing serum bank (4058 serum samples) representative of the Flemish population. All age groups between 0 and 100 years were included. A tissue (Vero cell) culture toxin neutralisation assay was used to measure serum diph-theria antitoxin concentrations. The results showed that 43% of the Flemish population was protected against diphtheria (antitoxin titre, > or = 0.1 IU/ml), while 32% was susceptible (antitoxin titre, < 0.01 IU/ml); for 25%, protection was of limited duration (antitoxin titre, > or = 0.01 IU/ml and < 0.1 IU/ml). The proportion of susceptible subjects showed a significant age-related increase, with the highest values in the 35 to 44 and 45 to 54 age groups (57.9% and 55.5%, respectively). These results emphasise the need for booster immunization of adults.

Adjuvanticity of pGPL-Mc and LRS in the immune responses of monkeys to oral immunization with diphtheria and tetanus toxoids

Experiments were carried out to examine the adjuvanticity of polar glycopeptidolipids of Mycobacterium chelonae (pGPL-Mc) or the London rocket seed (LRS) when combined with diphtheria and tetanus toxoids in an oral immunization of the African green monkey. The results showed that none of the monkeys receiving diphtheria and tetanus toxoids combined with 25 mg/kg of pGPL-Mc showed an increase in the the level of diphtheria antitoxin (DA) on the third and sixth weeks following the first and the second immunizations. One monkey from this group responded with increased seroneutralizing antibodies 3 weeks after the third feeding. On the other hand, one monkey, 3 weeks after the first immunization, and three monkeys, 3 weeks after the second and third oral vaccinations, showed an increase in specific anti-diphtheria antibody responses when the toxoids were combined with 25 mg/kg of LRS. The anti-diphtheria antitoxin responses of monkeys receiving diphtheria and tetanus toxoids combined with 50 mg/kg of pGPL-Mc or 50 mg/kg of LRS were significantly enhanced compared to the groups administered 25 mg/kg of the two adjuvants. The increase was observed in four out of five pGPL-Mc administered and in three out of five LRS-receiving monkeys. The results show that pGPL-Mc induced the highest titres of anti-diphtheria antitoxin compared to LRS, whereas the level of anti-diphtheria antitoxin titre of the two monkeys receiving the toxoids alone was less than 0.1 i.u./ml of serum throughout the experiment. According to the statistical analyses, no significant differences were recorded between the diphtheria antitoxin responses of monkeys following the first, second or third administration of LRS-adjuvated diphtheria and tetanus toxoids. However, a significant difference (P < or = 0.05) was observed in the diphtheria antitoxin response between the first and the second immunization of monkeys administered with toxoids adjuvated with 50 mg/kg of pGPL-Mc. The tetanus antitoxin responses of all monkeys were less than 0.1 i.u. of antitoxin per millilitre of serum throughout the study, which is considered not to be protective. However, we have recorded an anti-tetanus antitoxin titre of more than 0.2 i.u./ml of serum in one monkey that received diphtheria and tetanus toxoids combined with 50 mg/kg of pGPL-Mc.

Potency assay of diphtheria antitoxin in Vero cell microcultures

Laboratory conditions were established for the titration of diphtheria toxin and antitoxin in Vero Cell Cultures (CCT) and a comparison was made with the intradermal test (IDT) as currently used throughout the world. Working dilutions and cut off values were established by reading both the change in color of phenol red used as pH indicator and changes in cell viability in the microscope. CCT shows high reproducibility and higher detectability than IDT in the titration of both WHO Reference Standard and high titer horse antisera. In sera of guinea pigs immunized for potency testing of diphtheria toxoid the titre was approximately 10 times lower than in the IDT. The explanation is a subject of speculation. The Vero cell titration might be adopted as such for titration of diphtheria antitoxin. In the case of the toxoid potency test it could be used if the limit for the titration is adjusted to 0.2 IU considering the equivalence obtained between the two tests, by taking into account a ratio of 1:10 between CCT and IDT.

Comparison of in vivo and in vitro methods for determining unitage of diphtheria antitoxin in adsorbed diphtheria-tetanus (DT) and diphtheria-tetanus-pertussis (DTP) vaccines

In view of the current efforts to find a reliable in vitro method which can suitably act as an alternative for determining the potency of the diphtheria component in a combined vaccine, we have analysed experimental batches by the method proposed by WHO [1] i.e. challenge method in guinea pigs. The same batches were also analysed by the alternative antibody induction method as suggested in the Indian Pharmacopoeia (I.P.) [2] which is similar to the old method suggested in the British Pharmacopoeia (B.P.) 1973. As per I.P. the initial part of raising the antibodies remains unaltered but the actual titration of diphtheria antitoxin from the immunised guinea pigs was performed by using the following in vitro methods: a) indirect haemagglutination test using human "O" red blood cells to coat diphtheria toxoid using chromic chloride as the coupling agent [3]; b) toxin neutralisation test using Vero cells [4]; c) a double diffusion technique in agar gel for titration of diphtheria antitoxin [5]. Our findings show clearly that the results of two in vivo methods i.e. Challenge Test, Alternative I.P. Method and the above-mentioned three in vitro methods are comparable and would certainly reduce the number of animals required by making a combination of in vivo and in vitro techniques to give us an assessment of the potency of the vaccine to be tested.

[Granule-accumulation in VERO cells used for determination of antitoxin titration by micro cell culture method: I. Influence of mouse serum]

When the titration of diphtheria antitoxin of mouse serum was carried out by micro cell culture method using VERO cells, a large number of granules were observed in the cells. In order to examine the influence of this phenomenon on the titration of antitoxin, kinetics of the granule-accumulation was investigated. The granule-accumulation occurred in the cells in the culture medium to which either immunized or normal mouse serum was added. The granule-rich cells appeared at the dilution of the serum less than 1:32 and increased in number with the concentration of the serum. After 4 days of incubation 88% of the cells showed granule-accumulation when undiluted serum was added. Besides the mouse serum, those from guinea-pigs, horses, fetal calves and humans were examined. However, intensive accumulation of granules such as shown with mouse serum was not observed. From these results it was suggested that mouse serum might have some unknown mechanism which caused the remarkable accumulation of granules in VERO cells. The nature of granule and influence of this phenomenon on the titration of diphtheria antitoxin will be presented in an accompanying paper.

[The kinetics of vaccine antibodies against tetanus toxoid, diphtheria toxoid, measles virus, poliomyelitis virus and pneumococcus after allogeneic and autologous bone marrow transplantation and revaccination. 3: The kinetics of vaccine antibodies against tetanus toxoid and diphtheria toxoid after allogeneic and autologous bone marrow transplantation and combined revaccination against diphtheria and tetanus]

The 3rd part of the paper deals with the results of a combined revaccination against diphtheria and tetanus in a group of 25 children after allogeneic bone marrow transplantation (BMT) with and without graft versus host disease (GvHD) and after autologous transplantation. It can be shown that in the allogeneic transplanted groups with and without GvHD it is possible to build up a tetanus and diphtheria antitoxin titre in a safe protective cause by a 2nd basic immunisation consisting of 3 single vaccinations starting about 9 to 12 months later. For autologous transplanted children only 1 to 2 vaccinations at a later term than for the allogeneic transplanted children may possibly be sufficient.

[Kinetics of vaccination antibodies against tetanus toxoid, diphtheria toxoid, measles virus, poliomyelitis virus and pneumococcus after allogenic and autologous bone marrow transplantation and booster vaccination. 2: Kinetics of vaccination antibodies against diphtheria toxoid after allogenic and autologous bone marrow transplantation]

In the second part of the paper we report on the results of the diphtheria antitoxin valuation of 8 children after allogeneic bone marrow transplantation (BMT) with and without graft versus host disease (GvHD) as well as on the kinetics of the diphtheria antitoxin of 5 children after allogeneic BMT with and without GvHD and of 5 children after autologous transplantation. The antibody valuation was done by a cell-culture assay. Whereas the inspection of the isolated data gives the impression of a swift antibody decrease up to the non-protective level from the 7th month after BMT, the kinetic tests are more highly differentiated. Besides rapidly decreasing values below the accepted protection rate of 0.01 IU/ml in the allogeneic transplanted groups, there are patients with positive antibody titres within an observation period of up to 24 months after BMT in the allogeneic as well as in the autologous transplantation group.

Immunization response varies with intensity of acute lymphoblastic leukemia therapy

Twenty-four children receiving maintenance chemotherapy for acute lymphoblastic leukemia were given booster doses of tetanus-diphtheria combined toxoids. One month later, 19 of the 24 children were given Haemophilus influenzae B oligosaccharide-cross-reacting material conjugate vaccine. Following immunization, all patients had protective antibody titers against tetanus, 92% had protective antidiphtheria titers, and 84% had protective titers against H influenzae. Preimmunization titers, postimmunization titers, and response to immunization varied according to the intensity of therapy. There was no correlation with duration of therapy or quantitative hematologic values in the peripheral blood. These observations support the recommendation that children treated for acute lymphoblastic leukemia should be immunized against H influenzae B.

Persistence of antibody after accelerated immunisation with diphtheria/tetanus/pertussis vaccine

OBJECTIVE

To determine the persistence of antibody to diphtheria, tetanus, and pertussis in children receiving an accelerated schedule of primary immunisation.

DESIGN

Controlled study of antibody testing of blood samples from children immunised according to various schedules: three doses of triple vaccine completed at 8-13 calendar months, 6-7 calendar months, before 6 calendar months, or three doses followed by diphtheria/tetanus before age 2.

SETTING

Plymouth Health Authority.

SUBJECTS

129 children aged 4 years who had received three doses of diphtheria/tetanus/pertussis vaccine with or without a diphtheria/tetanus booster.

MAIN OUTCOME MEASURES

Diphtheria and tetanus antitoxin concentrations and antibody titres to pertussis toxin, filamentous haemagglutinin, and agglutinogens 2 and 3.

RESULTS

All children had protective concentrations of antitoxin to diphtheria and tetanus (greater than or equal to 0.01 IU/ml). There was no evidence of a significant difference in diphtheria or tetanus antitoxin concentrations and pertussis antibody titres in children immunised with an accelerated course (third dose of triple vaccine before 6 months) compared with those who received a longer course (third dose at 8-13 months) with no booster (geometric mean antitoxin concentration 0.411 (95% confidence interval 0.273 to 0.618) v 0.426 (0.294 to 0.616) for diphtheria and 0.358 (0.231 to 0.556) v 0.299 (0.197 to 0.453) for tetanus; geometric mean antibody titres 903 (500 to 1631) v 1386 (848 to 2266) for pertussis filamentous haemagglutinin, 179 (130 to 248) v 232 (167 to 322) for pertussis toxin, and 2002 (1276 to 3142) v 3591 (2220 to 5809) for agglutinogens 2 and 3).

CONCLUSION

Immunisation with three doses of triple vaccine at monthly intervals completed before 6 months of age probably provides adequate protection against diphtheria, tetanus, and whooping cough which will persist until the age of the preschool booster.

Determination of diphtheria toxin neutralizing antibody titers with a cell protein synthesis inhibition assay

A method which allows an accurate determination of very low titers of antibodies able to neutralize diphtheria toxin has been developed. The assay is based on the incubation of a reference amount of diphtheria toxin with different dilution of the serum and the evaluation of the residual toxicity of diphtheria toxin on Vero cells. The cells are seeded in 96-well plastic plates with the toxin-serum mixtures and the residual toxin activity is measured as the block of cell protein synthesis after incubation with [14C]leucine. Antitoxin titers as low as 0.002 IU can be reproducibly and accurately measured and the method gives a linear response in the range 0.002 to 8.0 IU/ml.

Immunity against diphtheria in the age group 15 to 25 years

Levels of diphtheria antitoxin in 254 serum samples were estimated in subjects in the age group 15 to 25 years with no previous history of immunisation against diphtheria using indirect haemagglutination test. All the individuals showed more than 0.03 IU/ml of diphtheria antitoxin level. This indicates that the age group studied was not susceptible to diphtheria. No significant relationship could be, however, ascertained between diphtheria antitoxin level and epidemiological factors like age, area (rural/urban), socioeconomic status, family size, education status and religion.

[Diphtheria antitoxin levels in Japanese adults (10-20 years after the last vaccination)]

The serum diphtheria antitoxin levels in Japanese adults were investigated and the persistence of diphtheria toxoid effect was evaluated. The subjects consisted of 56 volunteers (20-31 years of age) who had received regular inoculations of diphtheria and pertussis vaccine (I and II or III phases). They had been immunized according to the Vaccination Law (old version) revised in 1958. The length of time after the last inoculation of diphtheria toxoid was speculated to range from 10 to 20 years. Serum diphtheria antitoxin was determined by passive hemagglutination method. Antitoxin level was 0.025 HAU/ml in 1 subject (1.8%), 0.05 in 2 (3.6%), 0.1 in 2 (3.6%), 0.2 in 8 (14.3%), 0.4 in 7 (12.5%), 0.8 in 12 (21.4%), 1.6 in 7 (12.5%) and more than 1.6 in 17 (30.4%). Results indicated that 55 of 56 (98.2%) possessed a higher level than the prophylaxis standard (0.05 HAU/ml). Since the current Vaccination Law prescribes a lower amount and fewer inoculations than the old law, the number of adults possessing prophylactic antitoxin level may decrease in the future. Further investigation of antitoxin level in adults needs to be continued.

[Microtiter enzyme-linked immunosorbent assay for diphtheria antitoxin in human sera--application of parallel line assay method]

The antibodies against Diphtheria toxin in human sera were measured by the ELISA method and the antitoxin titer was calculated using the parallel line assay method which is a quantitative bioassay method. The reproducibility of this method and the comparison of the titer between this method and cell culture method were proven. The dose response curve of standard antiserum and test serum calculated by the parallel line assay method showed linearity, and the regression line of the test serum was parallel to the standard serum. The coefficients of variance (CV) of the antitoxin titers obtained from triplicate measurements of 3 serum samples ranged from 9.1 to 36.0%. The serum at low titer gave a higher CV level. A good correlation was observed between the Diphtheria antitoxin titer by the neutralizing test in cultured cells and that measured by ELISA by the parallel line assay method. The coefficient of regression was 0.996 and the coefficient of the correlation was 0.899.

Routine immunisation of preterm infants

Fifty one preterm infants (26-36 weeks' gestation) were enrolled in a study of their immunological responses to diphtheria, tetanus, pertussis, and polio antigens eight to 12 weeks after their primary courses had been completed. Samples from 21 infants born at full term were also analysed. Many infants were able to start immunisation at 3 months of age. Premature infants who are immunised as soon as possible after 3 months of age develop adequate antibody responses.

In vitro induction of a diphtheria toxoid specific antibody response in human peripheral blood lymphocytes cultivated in the presence of diphtheria toxoid

In comparison with the presently used potency test for diphtheria vaccine, in vitro examination of the immunogenicity of the vaccine would have great advantages. For this reason in vitro induction of diphtheria toxoid specific antibody synthesis in human peripheral blood lymphocytes cultivated in the presence of diphtheria toxoid was investigated. The results showed that a dose dependent synthesis of diphtheria antibody was induced by adsorbed diphtheria toxoid and combined vaccines containing the diphtheria toxoid component. Plain diphtheria toxoid appeared to be less immunogenic in comparison with adsorbed toxoid. There is some indication that the pertussis component had a stimulating effect on the diphtheria antibody synthesis. In conclusion, these results are promising for in vitro examination of the immunogenicity of diphtheria vaccines. The model will be validated for the routine control of diphtheria vaccine.

Immunity to diphtheria in a sample of adult population from central Italy

A sample of 643 healthy subjects from central Italy aged 20 to 80, were screened for diphtheria antitoxin. Serum diphtheria antitoxin was assayed by a new passive haemagglutination technique using turkey red blood cells sensitized with diphtheria toxoid, after having performed a correlation study between this technique and the reference in vivo neutralization test. Of the studied population 26.7% showed a lack of serum antitoxin titres considered to be protective. The rate of susceptible subjects increased with age, showing the highest value (38.9%) in the sixth decade of age. Males proved less protected than females; 53.2% of the male population aged 50-59 were lacking a protective anti-diphtheria immunity. On the basis of present results, a periodical revaccination of the entire adult population with reduced doses of diphtheria toxoid would be advisable.

Diphtheria in Stockholm, with a theory concerning transmission

Since 1984, diphtheria has been diagnosed in Sweden, mainly among men abusing alcohol. During the first half of 1986, eight cases of diphtheria were discovered in the city of Stockholm. The first three were among men abusing alcohol. The following five cases had no connection with them. These five persons were employed in two companies housed in the same building. The only connection between them was that they ate their lunch at the same restaurant. One alcohol-abusing man had worked temporarily in the kitchen of this restaurant during the week before the five cases of diphtheria arose. He knew one of the first three patients well. A throat swab taken from him a month after the five cases had been diagnosed was negative. It was suspected however, that this man might have been a carrier of Corynebacterium diphtheriae during the week that he worked in the kitchen. Tests for C. diphtheriae antitoxin revealed that the kitchen staff had high antitoxin titres although they lacked a history of basic immunisation. Even so, C. diphtheriae could not be isolated from their throats and it has not been possible to establish the mode of transmission. The most reasonable theory of transmission is that the organism was introduced into the kitchen by the man employed there temporarily and that it was spread by food served in the restaurant. This theory has not been proved but is discussed in order to facilitate future investigations of a similar outbreak.

Comparison of immune responses to diphtheria and tetanus toxoids of various mouse strains

Immune responses of 11 mouse strains with known genetical characteristics and two outbred strains to diphtheria and to tetanus toxoids were compared. Both diphtheria and tetanus antitoxins were titrated by passive hemagglutination. From the pattern of the immune response, the mouse strains tested may be classified into four groups. [1] Strains ddY (SPF) and ddY (conv) and those with haplotype H-2b, such as C57BL/6 and C57BL/10, were high responders to both toxoids. [2] Strains with H-2d, such as BALB/c, B10.D2 and DBA/2Cr, were intermediate responders to both toxoids. [3] Strains with H-2k, H-2a or, H-2m, such as C3H/He, B10.BR, B10.BR/SgSn, B10.A/SgSnJ and B10.AKM/O1a, were high responders to diphtheria toxoid but low responders to tetanus toxoid. [4] The strain with H-2h4, B10.A (4R), was a poor responder to both toxoids.

Combined estimation of tetanus and diphtheria antitoxin in human sera by the in vitro Toxin-Binding Inhibition (ToBI) test

The use of the principle of inhibition of toxin binding to an antitoxin coated immunoassay plate as described in a previous paper for tetanus antitoxin titration, was adapted for the estimation of diphtheria antitoxin in human sera. With a few modifications, a Toxin-Binding Inhibition (ToBI) test was developed which could be used for a combined estimation of both tetanus and diphtheria antitoxin levels. The application of streptavidin-biotinylated peroxidase complex when using small serum samples (less than 50 microliters) is discussed. Antitoxin titres (both diphtheria and tetanus) of 0.002 IU ml-1 were detectable by the ToBI test, this being far below the level considered to be protective in man. Sera from 140 adults with different vaccination histories were titrated for both tetanus and diphtheria antitoxin. Good correlations were found between the estimates obtained by the ToBI test and those obtained by the toxin-neutralization (TN) test in mice (tetanus antitoxin) and those obtained in the in vitro neutralization test in VERO cells (diphtheria antitoxin). It is concluded that the ToBI test is a simple and reliable alternative to the functional models currently in use for the estimation of diphtheria and tetanus antitoxin levels. In addition, the ToBI test eliminates the need for laboratory-animal or cell-culture facilities and can be performed with small quantities of serum as required in field trials.

Immunity and immunization of children against diphtheria in Sweden

The level of immunity to diphtheria and the effect of vaccination with different doses of diphtheria toxoid was investigated. The 457 study children, 6, 10 and 16 years of age, had as infants received routine primary vaccination with three doses of diphtheria-tetanus-toxoid or diphtheria-tetanus-pertussis vaccine, and the 16 year-olds also had received a booster dose of tetanus with a small dose of diphtheria at the age of ten. Prior to the study booster, 15% of the 6-year-olds had antitoxin levels against diphtheria less than 0.01 IU/ml, the given minimum level for protection. Of the 10-year-olds, 48% had titres less than 0.01 IU/ml, while the corresponding figure for the 16-year-olds was 24%. After a booster injection of 0.1, 0.25 or 0.5 ml of diphtheria-tetanus vaccine, more than 97% of the children showed titre levels greater than or equal to 0.1 IU/ml, while levels of greater than or equal to 1 IU/ml, indicating titres sufficient for long-term protection, were attained by 23-96%. Systemic reactions were few and moderate. Local reactions were of little clinical significance. In a group of 5-years-olds given diphtheria-tetanus primary vaccinations over wider intervals, only 1.4% had antitoxin titres less than 0.01 IU/ml. The results show a need for serologic monitoring of vaccination programmes.

Immunity to diphtheria, six to 15 years after a basic three-dose immunization schedule

The results of a study of the immunity to diphtheria of 283 girls (9-18 years of age) vaccinated at the age of two years with three doses of vaccine, are reported. The rabbit skin test was used to determine the titre of serum diphtheria antitoxin. 55.8% of the subjects were found to be protected (titre greater than or equal to 0.1 IU/ml), 38.9% were only relatively immune (titre greater than or equal to 0.01- less than 0.01 IU/ml), and 5.3% were unprotected (titre less than 0.01 IU/ml). The antitoxin titres showed a tendency to decrease with time. Even so, 6-15 years after vaccination, the percentages of protected and partially protected subjects were still high (95%).

Estimation of Corynebacterium diphtheriae antitoxin in human sera: a comparison of an enzyme-linked immunosorbent assay with the toxin neutralisation test

Serum samples from 101 individuals were titrated for Corynebacterium diphtheriae antitoxin by an IgG-specific enzyme-linked immunosorbent assay (ELISA) and a neutralisation test in tissue culture (TC). In some of the sera, the concentrations of antitoxin determined by the two assays were different; antitoxin values in these sera were titrated again by neutralisation tests in guinea pigs (GNT). Antitoxin concentrations of greater than 0.01 IU/ml by GNT partly corresponded to values obtained in both ELISA and TC. Only the values from TC agreed with lower GNT results. Heat inactivation of sera was investigated and rejected as a possible reason for the discrepancy in the results. ELISA can be used to detect levels of less than 0.1 IU/ml, although the accuracy below 0.01 IU/ml, often considered a protective level, is questionable. At higher levels ELISA was reproducible for the titration of diphtheria antitoxin in human sera and offers a useful alternative to both in-vivo assays and TC.

[Indices of diphtheria (antitoxic) immunity in the dynamics of the disease and its treatment in adults]

A total of 1,034 serum samples from 618 persons, including patients with different forms of diphtheria, carriers of the toxigenic forms of Corynebacterium diphtheriae, and angina patients, were studied. Analysis of the incidence of antibodies to C. diphtheriae toxin and their titers revealed that in more than half of all diphtheria patients no antibodies to C. diphtheriae toxin were detected upon admission to hospital. At the same time in 26% of the patients no antibodies were detected during the whole period of the disease; in such patients the toxic and subtoxic forms of diphtheria were registered twice as often as in seropositive patients. In 31% of the patients seronegative by the moment of hospitalization a rapid increase in the titers of antibodies C. diphtheriae toxin was observed in the course of the disease, which was indicative of the secondary character of immune response in patients who had been immunized earlier.

Immunity against diphtheria and tetanus in the age group 30-70 years

In Denmark, childhood primary vaccination against diphtheria and tetanus has been recommended since 1950. No routine revaccinations or general vaccination of adults have been offered. In most other western countries revaccinations are recommended later in childhood. However, death still occurs from diphtheria and tetanus in countries with such vaccination programs although it is generally accepted that protective immunity can be obtained by vaccination. On this basis the immunity against diphtheria and tetanus was assessed in a random sample of 351 subjects in the age range 30-70 years. Diphtheria antitoxin titres were determined by in vitro neutralization technique using VERO cells. 26% had diphtheria antitoxin titres below protective level (0.01 international antitoxin units/ml serum). The highest number of unprotected against diphtheria was found among 30-39 year old women (68%) and 60-69 year old subjects (36%). Tetanus titres were determined by a combination of ELISA technique and an in vivo neutralization assay. 51% were unprotected against tetanus (less than 0.01 international antitoxin units/ml serum). The highest number of unprotected against tetanus was found among 60-69 year old subjects (68%) and especially among females in this age group (77%). To avoid epidemics of diphtheria in the future the immunity among adults must be raised within the coming years. Thus, revaccination must be recommended and high attendance ensured. One revaccination is sufficient only when complete primary vaccination is documented.

Adverse reactions and immunogenicity in adults to regular and increased dosage of diphtheria vaccine

Booster doses of 3 Lf or 7.5 Lf of a regular diphtheria vaccine were given to 200 previously immunized adult volunteers. The toxoid was prepared from toxin with a purity of 2100 Lf/mg protein nitrogen and adsorbed to aluminium phosphate. Systemic reactions were rare and no severe symptoms were observed. Local reactions occurred in 40-50% of the vaccinees, but in only 7.5% were they of clinical significance, i.e. an area of redness/swelling greater than 5 cm. The two doses did not cause significant differences in reaction rates, and the 7.5 Lf dose elicited a better antitoxin response. Thus, a dose of 7.5 Lf diphtheria toxoid of similar purity can safely be given to adults in vaccines.

[Specific prevention of diphtheria in adults in foci of this infection]

The studies demonstrated the immunological and epidemiological effectiveness of a single injection of adsorbed diphtheria-tetanus toxoid with reduced antigen content for adults: intense antidiphtheria immunity in 92.3% of the vaccinees 1-3 months and in 94.5% of the vaccinees 1 year after the injection. This immunity remained sufficiently intense for 3 years (the term of observation). The geometric mean of antitoxic titers was 0.84 I. U./ml. The highest intensity of immunity appearing after the injection was observed in persons aged 18-20 years who showed the highest antitoxic titers (exceeding 0.5 I. U./ml) in 100% of cases, the lowest intensity was registered in the age group of 30-39 years; in 14.2% of these vaccinees antitoxic titers were below the protective level. In other age groups (40-49 years, 50 years and over) the intensity of immunity was high. The geometric mean of the titers of diphtheria antitoxin were 1.2 I. U./ml and 2.1 I. U./ml respectively. In none of the foci under study the spread of the manifest forms of the disease was observed.

Immunity to diphtheria in young British adults

Of 906 recruits aged between 16 and 20 years who were Schick-tested upon entry to the Royal Air Force, 775 were tested for circulating Corynebacterium diphtheriae antitioxin by means of an indirect haemagglutination (IHA) method. Of the total population, 95.7% were Schick-test negative, 3.5% were Schick-test positive and 0.8% gave pseudo-reactions. Of those tested by the IHA test, 37.7% were regarded as immune, 47.0% as 'immune-susceptible' and 15.3% as non-immune. Discrepancies between the two tests were discovered. Of those persons found to be Schick-test positive, 34.6% possessed circulating antitoxin; of those Schick-test negative, 13.5% were regarded as non-immune. A history of diphtheria immunisation in childhood was found to be a poor predictor of immunity. A protocol for selective diphtheria immunisation of adults is proposed.

[Immunological effectiveness of a 2d revaccination against diphtheria performed at intervals extended up to 7-10 years]

The present article deals with the data on the duration of antidiphtheria immunity, induced by the primary cycle of immunization with adsorbed DPT vaccine, with the aim of considering the problems of optimizing the immunization schedule for children. The prolongation of the interval before the second booster immunization to 7-10 years produces no negative influence on the effectiveness of immunization. Besides, the study has shown that after the main complex of immunizations with adsorbed DPT vaccine protective immunity to diphtheria is retained in 90.3-96.8% of children covered by this study for 9-10 years. These data point to high immunological effectiveness of adsorbed DPT vaccine and to the possibility of prolonging the intervals between booster immunizations to 10 years, as well as decreasing the number of booster immunizations in the immunization schedule for children.

The immunization of adults against diphtheria in Sweden

Two hundred and three women who disclaimed vaccination against diphtheria were divided into four groups and injected with either 2.0 or 6.25 Lf of a routine diphtheria toxoid or of a more purified preparation. One hundred and twenty-six of these women who did not show a secondary antibody response were given a second and a third injection one month and one year, respectively, after the first injection. Prebooster (third injection) antitoxin titres of greater than or equal to 0.01 IU ml-1 (the minimum level for protection) were found in 22 and 37% of those who received 2.0 and 6.25 Lf, respectively. Postbooster titres of greater than or equal to 1.0 IU ml-1 (calculated to give a protection of at least ten years of duration) were found in 23 and 58% of those who received 2.0 and 6.25 Lf, respectively. The rate of untoward reactions was low. Fever of short duration occurred in five women. Four out of the five women received 6.25 Lf of the more purified diphtheria toxoid and one 2 Lf of the routine toxoid. Local reactions greater than 10 cm were observed in three women. All received the higher dose, 6.25 Lf of diphtheria toxoid. Local reactions greater than 5 but less than or equal to 10 cm occurred in up to 13% (6.25 Lf of diphtheria toxoid). No significant difference between the groups of women vaccinated with routine or more purified toxoid was found. It was concluded that the diphtheria toxoids in the two doses of 2 Lf and 6.25 Lf did not induce a satisfactory immune response. To induce adequate protection the dose of diphtheria vaccine needs to be the same for adults and children, i.e. 12.5 Lf.

Antitoxic immunity of the population against diphtheria in Singapore

A serological study to evaluate the efficacy of the diphtheria immunisation programme in Singapore based on sera collected from 425 healthy persons between 6 months and 40+ years of age showed that 94.6% of the population surveyed possessed protective neutralising antitoxin (greater than or equal to 0.01 IU/ml). No sex or ethnic difference was noted. The most suspectible age-group was adults above 40 years of age in which 14.3% had no protective antitoxic immunity against diphtheria (less than 0.01 IU/ml). The geometric mean titre was generally high with sharp anamnestic type of secondary response elicited by periodic boosters administered. The survey confirmed the efficacy of the childhood immunisation programme which extended from 3 months to 15+ years of age, in maintaining a high level of herd immunity of the population right into adulthood. Further extension of the programme to include routine revaccination of adults was not considered necessary.

The immunization of children with combined diphtheria and tetanus vaccine in Sweden

Two groups derived from 97 children three-four months of age were vaccinated with diphtheria and tetanus vaccines containing either a routinely prepared diphtheria toxoid or a more purified preparation. Two injections were given with an interval of one month and a third injection was given one year after the first. Prior to the third injection no child was without protection against diphtheria, i.e. had an antitoxin titre less than 0.01 IU ml-1. After the third injection 95 and 94% of the children vaccinated with the routinely and more purified diphtheria toxoids, respectively, had diphtheria antitoxin titres greater than 1 IU ml-1 (estimated to provide protection for at least ten years). Systemic reactions such as fever and malaise occurred in five children. Local reactions greater than 10 cm were observed in three children and reactions greater than 5 but less than or equal to 10 cm were seen in 14% of the children. The routinely prepared combined diphtheria and tetanus vaccine, DT, produced very good immunity against diphtheria with moderate side effects. The use of a more purified diphtheria toxoid in the combined vaccine produced the same immunity and side effects.

Determination of tetanus and diphtheria antitoxin content in dried samples of capillary blood: a convenient method applied to infants

To assess the effect of vaccination of infants against tetanus and diphtheria capillary blood was drawn from 51 randomly selected healthy infants 2 years of age. The blood was applied directly to filter paper. In the laboratory the blood dots were eluted in phosphate buffered saline for 2 h at room temperature yielding 100% recovery of antitoxin activity. Serum volume in the blood dots was determined by calculation of dot area or by measuring albumin content in the eluted samples by means of rocket immunoelectrophoresis. These approaches were found to be equally applicable. Concentration of antitoxin to tetanus and diphtheria was assessed with ELISA and in vitro toxin neutralization assay respectively. Mean diphtheria antitoxin concentration was 0.53 IU/ml, and mean tetanus antitoxin concentration 4.1 IU/ml. Low initial immune response to diphtheria vaccination may be responsible for the risk among school children to have antitoxin concentration below protective level (reported elsewhere). In environments where diphtheria is disappearing a lowered vaccination response may be expected.

[Serological surveillance of diphtheria]

The serological method (indirect hemagglutination test) has been used in the surveillance of diphtheria infection. The structure of immunity to diphtheria in the population of the region has been studied. The possibility of increasing intervals between booster immunizations has been confirmed. The introduction of planned booster immunizations of the adult population with diphtheria toxoid is proposed.

Diphtheria vaccine for adults

A low dose (1.5 Lf) diphtheria vaccine for use in adults was given to 310 university student volunteers whose diphtheria antitoxin titres were less than 0.1 IU per ml. The incidence of adverse reactions was low. Postimmunisation blood samples taken from 134 of the students showed that in susceptible vaccinees the vaccine induced titres of antitoxin were consistent with protection and that it boosted the titres of those whose immunity was low.

Revaccination of adults against diphtheria. II: Combined diphtheria and tetanus revaccination with different doses of diphtheria toxoid 20 years after primary vaccination

Immunity following diphtheria vaccination in childhood is temporary, and recent outbreaks of diphtheria in adult populations evoked interest in the effect of and side-reactions to revaccination of adults. 237 military recruits were randomly allocated to revaccination with 6 Lf tetanus toxoid or 6 Lf tetanus toxoid combined with 2 Lf or 5 Lf diphtheria toxoid. Side-reactions were recorded one week later, and antitoxin response was assessed after 4 weeks. Protective serum diphtheria antitoxin levels were attained by all subjects receiving diphtheria toxoid containing vaccines. Antibody response was related to dose, indicating a safer long-term protection by revaccination with 5 Lf diphtheria toxoid. All vaccinees, except one without documentation for primary vaccination, attained high tetanus antitoxin levels. Interference phenomena between toxoids were insignificant. Mild local reactions were reported by 22% of the vaccinees. More pronounced local reactions were experienced by 5% and systemic reactions by 3%, independent of vaccine. No serious reactions were observed. Reactions were significantly related to tetanus antitoxin response only. It was concluded that combined revaccination of adults, primary vaccinated around 20 years previously, may be performed without immune assessments.