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PubMed1972

International collaborative studies on potency assays of diphtheria and tetanus toxoids.

Collaborative studies showed that relative potency assays for a particular type of diphtheria toxoid (adsorbed) and for tetanus toxoid (plain and adsorbed) gave very similar results, whether the assays were carried out by toxin challenge or by antitoxin titration after immunization of experimental animals with graded doses of toxoid. The same numerical results were obtained with a scoring system as with a system based on survivals only. Although skin tests were used on a very limited scale in these studies, it seems likely that they could replace lethal tests for the diphtheria challenge assays.For both tetanus and diphtheria, the adsorbed toxoid gave a higher relative potency when combined with other antigens than as a single toxoid. Both mice and guinea-pigs were used for the lethal challenge test of adsorbed tetanus toxoid. For the single tetanus toxoid the results were the same, but for the combined toxoid (DPT vaccine) the mouse assay results were about twice those of guinea-pig assays.

Animals↗
PubMed1975

Early and enhanced antioxin responses elicited with complexes of tetanus toxoid and specific mouse and human antibodies.

Primary tetanus antitoxin responses were early and enhanced in mice when tetanus toxoid was administered in complex with specific isologous antitoxin or specific mouse gamma-globulin. Antoxin responses were enhanced when fluid tetanus toxoid was complexed in vitro in antigen-to-antibody ratios of equivalence or antigen excess; responses to complexed toxoid in antibody excess were comparatively repressed. Primarly responses were greatly inhibited in mice immunized with the same amount ot toxoid complexed in vitro in antigen-to-antibody ratios of equivalence or antigen excess; responses to complexed toxoid in antibody excess were comparatively repressed. Primary responses were greatly inhibited in mice immunized with the same amount of toxoid complexed at equivalence or in antibody excell with specific human gamma-globulin. Although primary responses. Separate injections of antigen and antibody at different sites produced an excelldnt antitoxin responses. Separate injections of antigen and antibody at different sites produced an excellent in vivo primed state for early and high responses. Antibody production after stimulation with complexed toxoid was also enhanced in mice irradiated with 400 rad, a dose that ordinarily completely suppresses primary responses with fluid toxoid alone. These data provide evidence for the efficacy of antigen-antibody complexes in early and active immunization.

Animals↗
PubMed1978

Antigenicity of purified glutaraldehyde-treated cholera toxoid administered orally.

The antigenicity of orally administered glutaraldehyde-treated cholera toxoid was investigated in healthy volunteers. Fourteen volunteers ingested two or three 2-mg doses of toxoid with saline, with the doses spaced at 28-day intervals. Thirteen other volunteers received comparable toxoid doses with NaHCO3 and milk to neutralize gastric acid. Increments in circulating antitoxin levels were used to assay the antigenicity of oral toxoid. Antitoxin was measured by adrenal cell, rabbit skin permeability factor, and passive hemagglutination assays in sera collected on days 0, 28, 35, 56, 63, and 84 after primary immunization. Adrenal cell and rabbit skin assays exhibited identical sensitivity in detecting antitoxin rises in the 27 vaccinees (19/27) and were significantly more sensitive than passive hemagglutination (11/27) (P less than 0.03). Volunteers who ingested toxoid with NaHCO3 and milk had a higher rate of seroconversion (77%) than those who received toxoid with saline (64%); they also had earlier rises in antitoxin titer and consistently higher geometric mean titers on all days tested. These studies demonstrate that purified cholera toxoid is antigenic in humans after oral administration. The possible role of oral toxoid in enhancing the protective effect of killed whole-cell vaccines can now be investigated.

Adult↗
PubMed1991

Biodegradable and biocompatible poly(DL-lactide-co-glycolide) microspheres as an adjuvant for staphylococcal enterotoxin B toxoid which enhances the level of toxin-neutralizing antibodies.

Microspheres composed of biocompatible, biodegradable poly(DL-lactide-co-glycolide) (DL-PLG) and staphylococcal enterotoxin B (SEB) toxoid were evaluated as a vaccine delivery system when subcutaneously injected into mice. As measured by circulating immunoglobulin G (IgG) antitoxin titers, the delivery of SEB toxoid via DL-PLG microspheres, 1 to 10 microns in diameter, induced an immune response which was approximately 500 times that seen with nonencapsulated toxoid. The kinetics, magnitude, and duration of the antitoxin response induced with microencapsulated toxoid were similar to those obtained when an equal toxoid dose was administered as an emulsion with complete Freund adjuvant. However, the microspheres did not induce the inflammation and granulomata formation seen with complete Freund adjuvant. The adjuvant activity of the microspheres was not dependent on the superantigenicity of SEB toxin and was equally effective at potentiating circulating IgG antitrinitrophenyl levels in response to microencapsulated trinitrophenyl-keyhole limpet hemocyanin. Empty DL-PLG microspheres were not mitogenic, and SEB toxoid injected as a mixture with empty DL-PLG microspheres was no more effective as an immunogen than toxoid alone. Antigen-containing microspheres 1 to 10 microns in diameter exhibited stronger adjuvant activity than those greater than 10 microns, which correlated with the delivery of the 1- to 10-microns, but not the greater than 10-microns, microspheres into the draining lymph nodes within macrophages. The antibody response induced through immunization with microencapsulated SEB toxoid was protective against the weight loss and splenic V beta 8+ T-cell expansion induced by intravenous toxin administration. These results show that DL-PLG microsphere vaccine delivery systems, which are composed of pharmaceutically acceptable components, possess a strong adjuvant activity for their encapsulated antigens.

Adjuvants, Immunologic↗
PubMed2005

Diphtheria, tetanus and pertussis antibodies in 10-year-old children before and after a booster dose of three toxoids: implications for the timing of a booster dose.

UNLABELLED: In an open study, 502 10-year-old children, who had received primary vaccination against diphtheria and tetanus in infancy and had varying histories of pertussis disease and vaccination, were vaccinated with diphtheria-tetanus vaccine (DT) alone or with the addition of 20 microg or 40 microg of pertussis toxoid. Diphtheria toxin neutralising antibodies, pertussis toxin IgG and tetanus toxoid IgG antibodies were measured before and 1 month after the booster. All toxoids were highly immunogenic. In pertussis toxoid recipients, median levels of pertussis toxin IgG increased to 16.5 U/ml (DTaP20) and to 36 U/ml (DTaP40) in children with non-detectable (<1 U/ml) antibodies before vaccination and to >400 U/ml in children (both DTaP20 and DTaP40) with detectable antibodies before vaccination. A total of 60 children (12%) with non-detectable (<0.01 IU/ml) diphtheria antibodies and 36 children (7%) with non-detectable (<0.01 IU/ml) tetanus antibodies before the booster had lower median antibody concentrations post-vaccination than children with detectable antibodies before the booster (diphtheria: 5.12 vs. 20.48 IU/ml; tetanus: 4.0 vs. 10.0 IU/ml). There were no differences in diphtheria and tetanus antibodies after vaccination between children who did and did not receive pertussis toxoid. CONCLUSION: 10-year-old children with non-detectable diphtheria and tetanus antibodies before the booster had lower post-vaccination antibodies than those with detectable antibodies before the booster indicating a poor immunological memory. Addition of pertussis toxoid to diphtheria-tetanus vaccine did not affect the antibody responses to diphtheria and tetanus toxoids when the three toxoids were combined as a booster. Even though immunity to diphtheria and tetanus was only estimated by surrogate markers (serum antitoxin antibodies) the results indicate that a lower age for the booster dose of diphtheria-tetanus vaccine or diphtheria-tetanus acellular pertussis vaccine should be considered.

Antibodies, Bacterial↗
PubMed2000

Booster effect of low doses of tetanus toxoid in elderly vaccinees.

In order to improve the immunity to diphtheria, the recommended booster dose of diphtheria/tetanus vaccine for adults in Sweden was changed in 1986 from 0.5 ml of tetanus vaccine with a small diphtheria dose to 0.25 ml of a diphtheria/tetanus vaccine containing 7.5 Lf tetanus toxoid and 30 Lf diphtheria toxoid/ml. This change resulted in an increase in the dose of diphtheria toxoid from 0.5 Lf to 7.5 Lf, but a decrease in the recommended booster dose of tetanus toxoid from 3.75 Lf to 1.9 Lf. The aim of the present study was to investigate whether this lower dose of tetanus toxoid was also sufficiently protective for elderly people. Two hundred adults (median age 76 years, range 60-92 years) with no history of tetanus vaccination during the past 10 years volunteered for the study. One hundred two vaccinees were inoculated with 1.9 Lf tetanus toxoid (0.25 ml) and 98 with 3.75 Lf tetanus toxoid (0.5 ml). Paired serum samples were analysed by the toxin-binding inhibition assay. Side effects were few and mild, without significant differences between the groups. Response rates were similar, with the 3.75 Lf dose eliciting a marginally higher antitoxin response. The prevaccination geometric mean titre was the same for both groups: 0.03 IU/ml. Postvaccination geometric mean titres were 1.18 IU/ml for the 3.75 Lf group and 1.93 IU/ml for the 7.5 Lf group, respectively (difference not significant). Forty-seven percent of the vaccinees had a prevaccination titre of < or =0.01 IU/ml. Postvaccination, 85% had a titre >0.01 IU/ml. Booster vaccination with tetanus vaccine containing only 1.9 Lf of tetanus toxoid was thus found to induce an excellent immune response in elderly people, with few side effects resulting.

Aged↗
PubMed1998

Local and systemic responses against ricin toxin promoted by toxoid or peptide vaccines alone or in liposomal formulations.

The objective of this study was to develop a vaccine which would ultimately protect man from the lethal effects of inhaled ricin toxin. Porton rats have previously been protected from lethal quantities of inhaled ricin by subcutaneous (s.c.) ricin toxoid vaccine, but not without lung damage. This situation might be improved by an alternative vaccine such as the A chain of ricin, already known to protect against inhaled ricin. Another option would be to improve respiratory tract immunity by local vaccination in conjunction with liposomal formulation with a view to enhancing lung secretion of immune IgA. While boosted s.c. doses of ricin toxoid or A chain produced indistinguishable systemic immune responses 3 weeks later, when delivered by the intratracheal (i.t.) route, the A chain failed to elicit a specific immune response, unlike ricin toxoid. This situation was overcome by liposomal formulations and although ricin toxoid was readily encapsulated in liposomes, A chain was not. However, by simply mixing A chain and liposomes in the same weight ratio determined for liposomal toxoid, systemic immune responses for each formulation were indistinguishable 1 week after boosting. Ricin antibody responses in lung fluid monitored 1, 3, 7 and 14 days after i.t. challenge with ricin were statistically indistinguishable, but the group vaccinated with liposomal toxoid secreted 28.7% IgA compared with 0.9-14.9% for the A chain liposomal group. From this, it might be anticipated that the lungs would be better protected by liposomally-encapsulated ricin toxoid than by the A chain-liposome mixture.

Animals↗
PubMedDate not supplied

Immune response with biodegradable nanospheres and alum: studies in rabbits using staphylococcal enterotoxin B-toxoid.

In this study, the adjuvant effect of the sustained release biodegradable nanospheres (100-150 nm in diameter) has been compared with alum. Nanospheres were formulated using a biodegradable polylactic polyglycolic acid copolymer (PLGA, 50:50) containing Staphylococcal Enterotoxin B (SEB) toxoid as a model vaccine antigen. Systemic immune response of the nanospheres containing toxoid was studied in rabbits by subcutaneous immunization. The data demonstrated that approximately 30% of the toxoid activity was lost following its encapsulation into nanospheres. Under in vitro conditions, nanospheres demonstrated sustained release of the toxoid. However, only 20% of the antigenic toxoid was released over the first 2 weeks of the release study. Immunization of animals with equal doses of toxoid, either using nanospheres or alum induced a comparable systemic immune response (IgG, IgM and IgA). The immune response reached a maximum level at 7 weeks post-immunization, which then gradually declined with time. The booster dose of toxoid at 19 weeks, either using alum or nanospheres induced similar immune response in both the groups, but was greater than the primary immune response. The studies, thus, suggest that biodegradable nanospheres could be used as a vaccine adjuvant.

Adjuvants, Immunologic↗
PubMed1977

Antigenicity of cholera toxoid in humans.

A cholera toxoid was produced by heating of a purified cholera toxin and treatment of the resulting toxoid procholeragenoid with a formaldehyde solution. When given subcutaneously and intramuscularly to volunteers in doses of 3-100 microng, the toxoid produced no noteworthy side effects, but the injections produced a dose-dependent rise in level of toxin-neutralizing antibodies in serum. Administration of toxoid in combination with whole-cell vaccine induced antitoxin levels that seemed to be higher than those induced by toxoid alone, but statistical analysis revealed a significant difference only between titers after administration of 10 microng of toxoid alone and those after administration of 10 microng of toxoid in combination with whole-cell vaccine.

Antibody Formation↗
PubMed1990

Response to tetanus toxoid immunization after allogeneic bone marrow transplantation.

An ELISA was used to study long-term immunity and immunization responses to tetanus toxoid in 48 bone marrow transplant recipients. Among patients who were seropositive to tetanus before transplant, 51% had lost their seropositivity 1 year later. All patients who were not reimmunized with tetanus toxoid were seronegative 2 years after transplant. All patients who were seronegative before transplant remained seronegative 1 year later regardless of the donor's serologic status. There was no difference in the ability to remain seropositive to tetanus toxoid between patients with and without chronic graft-versus-host disease. Of 21 patients immunized with one dose of tetanus toxoid 1 year after transplant, 14 were seronegative at the time of immunization (response rate, 64%). At 1 year after immunization, 7 remained seropositive. Ten patients were reimmunized with two doses of tetanus toxoid. All responded and 90% remained seropositive 1 year later. When 21 patients were primarily immunized with three doses of tetanus toxoid, all patients seronegative at immunization responded and all tested patients remained seropositive 2 years later. The immunization responses were significantly superior in patients receiving three doses compared with those who received one. Reimmunization with tetanus toxoid of long-term survivors after marrow transplant seems necessary. A three-dose immunization schedule is recommended to obtain an adequate immune response.

Antibodies, Bacterial↗
PubMed2001

Safety and immunogenicity of increasing doses of a Clostridium difficile toxoid vaccine administered to healthy adults.

Clostridium difficile is a major cause of nosocomial diarrhea in industrialized countries. Although most illnesses respond to available therapy, infection can increase morbidity, prolong hospitalization, and produce life-threatening colitis. Vaccines are being explored as an alternative means for protecting high-risk individuals. We assessed the safety, immunogenicity, and dose response of a parenteral vaccine containing C. difficile toxoids A and B. Thirty healthy adults were assigned to receive four spaced inoculations on days 1, 8, 30, and 60 with one of three doses of vaccine (6.25, 25, or 100 microg). At each dose level, subjects were randomized, in a double-blind fashion, to receive either the soluble toxoids (n = 5) or toxoids adsorbed to alum (n = 5). Subjects were monitored for clinical and immunologic responses to vaccination. Vaccination was generally well tolerated, with occasional, usually mild, systemic reactions (abdominal pain, arthralgia, and diarrhea). The most common local reaction, mild arm pain, was reported by all recipients of the toxoid-alum formulation. Nearly all subjects (> or = 90%) developed vigorous serum antibody responses to both toxins, as measured by immunoglobulin G (IgG) enzyme-linked immunosorbent assay and neutralization of cytotoxicity, whereas fecal IgA increases occurred in approximately 50%. Statistically significant effects of dose and formulation on immunogenicity were not seen, although antibody levels tended to be higher with the alum-adjuvanted formulations and with increasing doses of soluble toxoid. Serum antibody responses among the toxoid-alum group appeared to plateau at 25 microg. We concluded that the C. difficile toxoid vaccine is safe and immunogenic in healthy volunteers. Further development as a prophylactic vaccine or for producing C. difficile hyperimmune globulin is justified.

Adolescent↗
PubMed1999

Stability of Russell's viper venom toxoid (lyophilized form) on storage.

A previously developed Russell's viper venom toxoid in Myanmar is in a liquid form that shows reversion in the form of a reduced number of formaldehyde linkages and toxicity during storage at 37 degrees C and at room temperature. In order to have a safe, potent and stable toxoid, a lyophilized form was prepared in the present study from the liquid toxoid through the use of a freeze dryer. Both the liquid and lyophilized forms were then stored at 4 degrees C and at room temperature, and in addition to safety and immunogenicity tests, biochemical parameters such as the protein content, the activity of venom enzymes (proteinase, phospholipase A, phosphodiesterase, and arginine esterase), and the released free formalin amounts were assessed at 3-month intervals over a period of 1 year. The results indicate that under both conditions, the lyophilized toxoid shows minimum changes in enzyme activity, a reduced tendency toward formaldehyde linkage, no toxicity, and more immunogenicity in comparison with the respective liquid toxoids. It could therefore be hypothesized that Russell's viper venom toxoid in a lyophilized form is more promising in terms of efficacy and stability for prophylactic use in human immunization than the conventional toxoid in a liquid form.

Animals↗
PubMed1975

[Experimental investigations on oral immunization with tetanus-toxoid (author's transl)].

Model-experiments in mice were used for the investigation of oral immunization with tetanus-toxoid. The efficacy of oral toxoid application was tested by challenge and anti-toxin determination. The oral immunization with tetanus-toxoid induced only a sufficient protection, when toxoid was in intensive contact with the mucous membranes of the oral cavity. Local immunization via gastro-intestinal-tract failed. After a single vaccination with 200 Lf tetanus-toxoid onto mucous membranes of the oral cavity the efficiency index was 75. In comparison, a single subcutaneous application of 2 Lf tetanus-toxoid resulted in an efficiency index of 100 and a single intranasal immunization of 100 Lf in an efficiency index of 93. So the application of toxoid subcutaneously or onto nasal mucous membranes induced higher protection than oral application. Temporary development of immunity after immunization via the mucous membranes of the oral cavity was much better than parenteral immunization. 20 per cent of orally immunized animals were immune 5 days p. vacc. At the same time subcutaneously immunized animals failed to develop any protection. The efficiency rates obtained in challenge correlate with antitoxin content in the serum.

Administration, Oral↗
PubMed1953

International standardization of diphtheria toxoids.

The present report is an analysis of results of assays of diphtheria toxoids carried out over a four-year period at the Laboratory of Hygiene, Department of National Health and Welfare, Ottawa, Canada. A single preparation, a crude monovalent diphtheria toxoid, was used as a reference standard for all types of preparation (purified, crude, or adsorbed). The results suggest that the use of such a standard is justified even though there is evidence to show that adsorbed and plain toxoids, and toxoids of different grades of purity, do not have identical immunization curves. The merits of the present International Standard for Diphtheria Toxoid, Plain, for the assay of all types of toxoid are discussed. The results suggest that this is not particularly suitable for adsorbed preparations, probably because of its flatter immunization curve. For the latter preparations, the proposed international standard for diphtheria toxoid, adsorbed, should prove more practical and useful.

Biological Assay↗
PubMedDate not supplied

Studies on adjuvants for human prophylactics. II. Influence of the route of injection on the activity of adjuvants to tetanus toxoid in guinea pigs.

The effects of the route of the injection and adjuvants on the immune response of guinea pigs were investigated at various stages of immune response to tetanus toxoid. Delayed-type hypersensitivity (DH) was observed as the first immune response to the toxoid before initiation of antitoxin production. The DH reaction was weak when plain toxoid was administered subcutaneously. Water-in-oil in water (w/o/w) enhanced greatly the reactivity of the immunized animals; pertussis vaccine, endotoxin and aluminium showed adjuvanticities in this order. The foot pad (fp) injection of plain toxoid promoted remarkably the induction of DH. The reactivity was enhanced considerably by w/o/w and to a less extent by aluminium. However, pertussis vaccine showed an adverse effect on DH by the fp route. Active cutaneous anaphylaxis (ACA) induced by the subcutaneous route was enhanced by w/o/w, endotoxin, pertussis vaccine and, to a less extent, by aluminium. The fp route compared with the sc route enhanced ACA by plain toxoid; w/o/w and aluminium but not endotoxin and the vaccine showed adjuvanticities. The influences of adjuvants and the route of injection on Arthus reactions were inconsistent. The effect of adjuvants on antitoxin production was quite different from that on DH when antitoxin was produced abundantly. Aluminium showed consistently a potent adjuvanticity, but activities of w/o/w, endotoxin and pertussis vaccine were inconsistent 4-6 weeks after the primary stimulus by the subcutaneous route. The adjuvant effect became less significant in the secondary response. The fp route was more favorable for antitoxin production than the subcutaneous route with most adjuvants except pertussis vaccine added to tetanus toxoid. Antitoxin production by plain toxoid was very poor when administered intraperitoneally; aluminium and w/o/w but not endotoxin showed a remarkable adjuvanticity for the antitoxin production.

Adjuvants, Immunologic↗
PubMed1989

Primary immune response to liposomal tetanus toxoid in mice: the effect of mediators.

Primary immune response (IgG1) to tetanus toxoid entrapped in liposomes composed of equimolar egg phosphatidylcholine and cholesterol, and the effect of a variety of physiological and non-physiological mediators (co-entrapped with the toxoid or entrapped in separate liposomes) on such responses, were studied in BALB/c mice. Results show that (i) primary responses, not detectable with the free antigen, were elicited with the same amount of antigen given in liposomes within a range (37.4:1-2857:1) of liposomal phospholipid to toxoid mass ratios. At a higher ratio (17,804:1) response was reduced to very low levels. Immune responses obtained with liposomal toxoid were maintained at measurable levels 24 weeks after immunization. (ii) Interleukin-2 (IL-2), interferon-gamma (IFN-gamma) and N-acetyl muramyl-L-threonyl-D-isoglutamine ([Thr1]MDP), but not its liposoluble 6-O-stearoyl derivative (6-O-S-[Thr1]MDP), co-entrapped with the toxoid at appropriate phospholipid to toxoid ratios, generally reduced primary response to levels below those achieved with liposomes containing the antigen alone. Further, responses obtained with 6-O-S[Thr1]MDP coentrapped with the toxoid or separately entrapped were higher than those seen with [Thr1]MDP in similar formulations. The significance of these findings is discussed in conjunction with the structural characteristics of liposomes.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1987

Liposomes as adjuvants with immunopurified tetanus toxoid: influence of liposomal characteristics.

The effect of various manipulations of liposomes composed of equimolar phospholipid and cholesterol on immune responses to the incorporated immunopurified tetanus toxoid was investigated in BALB/c mice. In studies designed to establish proper dosage for immunization and to reveal the roles of the liposomal phospholipid to toxoid mass ratio, gel-liquid crystalline transition temperatures (Tc) of the liposomal phospholipids and mode of antigen incorporation into liposomes on immune responses, animals were injected intramuscularly with various amounts of the toxoid, free, entrapped in multilamellar dehydration-rehydration vesicles (DRV) or covalently linked to the surface of multilamellar vesicles (MLV) prepared by the classical procedure. Two identical injections separated by 4 weeks were given and IgG1 and IgG2b antibodies specific for the toxoid assayed in sera by an enzyme-linked immunosorbent assay. Results suggest that the adjuvant effect of liposomes is improved considerably when liposomal phospholipid to toxoid mass ratios are as high as 2049:1; however, adjuvanticity is reduced to reach very low levels for much higher ratios (e.g. 90,361:1); antibody responses are similar for liposomes (phospholipid to toxoid mass ratios: 14.3-33.1) made of a variety of phospholipids with Tcs ranging from -32 degrees to 41.5 degrees but are low or non-existent when liposomes are made of distearoyl phosphatidylcholine (Tc, 54 degrees) (however, see Discussion); there are no differences in antibody responses between liposomes with entrapped and surface-linked toxoid.

Adjuvants, Immunologic↗
PubMed1972

Collaborative assay of a proposed international standard for tetanus toxoid (adsorbed).

An international collaborative assay was performed with the aim of establishing an international standard for tetanus toxoid (adsorbed). Six laboratories participated. A suitable preparation in the lyophilized state was made available by the Paul Ehrlich Institut, Frankfurt am Main, Federal Republic of Germany. Preliminary experiments showed that there were no significant differences between individual ampoules and that the preparation was highly thermostable.The proposed preparation (A) was compared in guinea-pigs and mice with the existing international standard for tetanus toxoid (B), which is a plain toxoid, with another arbitrarily chosen adsorbed toxoid (C), and with a number of locally prepared preparations (D). In the mouse tests preparation B was omitted. It was found in the guinea-pig tests that 1 mg of the proposed standard contained an activity equivalent to 1.5 IU if compared with the non-adsorbed international standard but since the slopes of the log dose-response lines for the adsorbed and plain types of preparation were not parallel, this is a rough approximation only. When the different adsorbed preparations were compared, there was close correlation between the guinea-pig tests and the mouse tests. In the guinea-pig test 1 ml of preparation C corresponded to 126.5 mg of preparation A and in the mouse test to 129.9 mg of preparation A. In one laboratory comparative tests were made by titrating blood antitoxins after immunization of guinea-pigs with graded doses of the toxoids. The results corresponded very well with the data from challenge tests (1 mg of preparation A contained 1.5 IU of the plain toxoid in challenge tests and|1.4 IU in the titration test).Preparation A was established by the WHO Expert Committee on Biological Standardization as the international standard for tetanus toxoid (adsorbed) and the international unit was defined as the activity contained in 0.6667 mg of the international standard.

Animals↗