Antibody Titers In Individuals Research Articles

Unveiling the seroprevalence of human papillomavirus in Guangdong, China: Implications for vaccination strategies.

Seroepidemiological characteristics of human papillomavirus (HPV) in community residents reflect natural infection and can guide the reform of vaccination programs. A population-based serological survey was conducted in Guangdong Province. Serum anti-HPV IgG antibody levels were determined by an ELISA. Neutralizing antibodies against HPV6, 11, 16, and 18 were detected via a pseudovirus-based neutralization assay (PBNA). A total of 5122 serum samples were collected from community residents, including 1989 males and 3133 females, in three cities of Guangdong Province. The rate of HPV IgG antibody positivity in females was 5.39% (95% CI: 4.6-6.2), which was greater than that in males (2.36%; 95% CI: 1.7-3.1). HPV IgG antibodies were more frequently detected in females aged 51-60 years (11.30%; 95% CI: 7.6-16.0), whereas in males, the detection increased with age and reached 4.94% (95% CI: 2.8-6.9) in the group aged ≥71 years. The seropositivity of neutralizing antibodies against HPV6 and 11 was greater than that against HPV16 and 18. The serum neutralizing antibody titers in individuals who received three doses of a vaccine were 7- to 12-fold greater than those in individuals who did not receive the vaccine. The neutralizing antibody titers slightly decreased within 40 months and ranged from 0.038 to 0.057 log ED50 per month. A moderate consistency between the HPV ELISA and PBNA results was observed (Kappa score = 0.49, r = 0.249, 0.635, 0.382, and 0.466 for HPV6, 11, 16, and 18, respectively). The HPV seropositivity rate among healthy residents of Guangdong Province was found to be low among children and adolescents and to increase with age. The serum neutralizing antibody titers were significantly greater in the vaccine group than that in the control group, and this difference persisted over time, which indicated promising protection against HPV infection.

Household immunity and individual risk of infection with dengue virus in a prospective, longitudinal cohort study.

Although it is known that household infections drive the transmission of dengue virus (DENV), it is unclear how household composition and the immune status of inhabitants affect the individual risk of infection. Most population-based studies to date have focused on paediatric cohorts because more severe forms of dengue mainly occur in children, and the role of adults in dengue transmission is understudied. Here we analysed data from a multigenerational cohort study of 470 households, comprising 2,860 individuals, in Kamphaeng Phet, Thailand, to evaluate risk factors for DENV infection. Using a gradient-boosted regression model trained on annual haemagglutination inhibition antibody titre inputs, we identified 1,049 infections, 90% of which were subclinical. By analysing imputed infections, we found that individual antibody titres, household composition and antibody titres of other members in the same household affect an individual's risk of DENV infection. Those individuals living in households with high average antibody titres, or households with more adults, had a reduced risk of infection. We propose that herd immunity to dengue acts at the household level and may provide insight into the drivers of the recent change in the shifting age distribution of dengue cases in Thailand.

Multi-phasic gene profiling using candidate gene approach predict the capacity of specific antibody production and maintenance following COVID-19 vaccination in Japanese population.

Vaccination against severe acute respiratory syndrome coronavirus type 2 is highly effective in preventing infection and reducing the severity of coronavirus disease (COVID-19). However, acquired humoral immunity wanes within six months. Focusing on the different tempo of acquisition and attenuation of specific antibody titers in individuals, we investigated the impact of genetic polymorphisms on antibody production after COVID-19 vaccination. In total 236 healthcare workers from a Japanese municipal hospital, who received two doses of the vaccine were recruited. We employed a candidate gene approach to identify the target genetic polymorphisms affecting antibody production after vaccination. DNA samples from the study populations were genotyped for 33 polymorphisms in 15 distinct candidate genes encoding proteins involved in antigen-presenting cell activation, T cell activation, T-B interaction, and B cell survival. We measured total anti-SARS-Cov2 spike IgG antibody titers and analyzed the association with genetic polymorphisms at several time points after vaccination using an unbiased statistical method, and stepwise logistic regression following multivariate regression. Significant associations were observed between seven SNPs in NLRP3, OAS1, IL12B, CTLA4, and IL4, and antibody titers at 3 weeks after the first vaccination as an initial response. Six SNPs in NLRP3, TNF, OAS1, IL12B, and CTLA4 were associated with high responders with serum antibody titer > 4000 BAU/ml as boosting effect at 3 weeks after the second vaccination. Analysis of long-term maintenance showed the significance of the three SNPs in IL12B, IL7R, and MIF for the maintenance of antibody titers and that in BAFF for attenuation of neutralizing antibodies. Finally, we proposed a predictive model composed of gene profiles to identify the individuals with rapid antibody attenuation by receiver operating characteristic (ROC) analysis (area under the curve (AUC)= 0.76, sensitivity = 82.5%, specificity=67.8%). The candidate gene approach successfully showed shifting responsible gene profiles and initial and boosting effect mainly related to the priming phase into antibody maintenance including B cell survival, which traces the phase of immune reactions. These gene profiles provide valuable information for further investigation of humoral immunity against COVID-19 and for building a strategy for personalized vaccine schedules.

Immune Response Kinetics Following a Third Heterologous BNT162b2 Booster Dose After Primary 2-Dose ChAdOx1 Vaccination in Relation to Omicron Breakthrough Infection: A Prospective Nationwide Cohort Study in South Korea.

Immune responses to each vaccine must be investigated to establish effective vaccination strategies for the ongoing coronavirus disease (COVID-19) pandemic. We investigated the long-term kinetics of immune responses after heterologous booster vaccination in relation to Omicron breakthrough infection (BI). Our study included 373 healthcare workers who received primary ChAdOx1 vaccine doses and a third BNT162b2 vaccine dose. BIs that occurred after the third vaccine were investigated. Blood specimens were collected before and 3 months after the booster dose from participants without BI and 1, 4, and 6 months after BI from participants who experienced BI. Spike-specific binding and neutralizing antibody levels against the wild-type virus, Omicron BA.1, and Omicron BA.5, as well as cellular responses, were analyzed. A total of 346 participants (82 in the no BI group; 192 in the BI group during the BA.1/BA.2 period; 72 in the BI group during the BA.5 period) were included in the analysis. Participants without BI exhibited the highest binding and neutralizing antibody concentrations and greatest cellular response 1 month after the third vaccination, which reached a nadir by the ninth month. Antibody and cellular responses in participants who experienced BI substantially increased postinfection. Neutralizing antibody titers in individuals who experienced BI during the BA.1/BA.2 period showed more robust increase against wild-type virus than against BA.1 and BA.5. Our findings provide evidence of antigenic imprinting in participants who received a heterologous booster vaccination, thereby serving as a foundation for further studies on the impact of BIs on immune responses.

Importance of Cellular Immunity and IFN-γ Concentration in Preventing SARS-CoV-2 Infection and Reinfection: A Cohort Study

Recent studies have highlighted the underestimated importance of the cellular immune response after the emergence of variants of concern (VOCs) of SARS-CoV-2, and the significantly reduced neutralizing power of antibody titers in individuals with previous SARS-CoV-2 infection or vaccination. Our study included 303 participants who were tested at St. Catherine Specialty Hospital using the Quan-T-Cell SARS-CoV-2 in combination with the Quan-T-Cell ELISA (Euroimmun Medizinische Labordiagnostika, Lübeck, Germany) for the analysis of IFN-γ concentration, and with Anti-SARS-CoV-2 QuantiVac ELISA IgG (Euroimmun Medizinische Labordiagnostika, Lübeck, Germany) for the detection of human antibodies of the immunoglobulin class IgG against the S1 domain of the SARS-CoV-2 spike protein. The statistical analysis showed a significant difference in the concentration of IFN-γ between reinfected participants and those without infection (p = 0.012). Participants who were not infected or reinfected with SARS-CoV-2 after vaccination and/or previous SARS-CoV-2 infection had a significantly higher level of cellular immunity. Furthermore, in individuals without additional vaccination, those who experienced infection/reinfection had significantly lower levels of IFN-γ compared to uninfected participants (p = 0.016). Our findings suggest a long-lasting effect of cellular immunity, measured by IFN-γ concentrations, which plays a key role in preventing infections and reinfections after the emergence of SARS-CoV-2 variants of concern.

Characterizing Longitudinal Antibody Responses in Recovered Individuals Following COVID-19 Infection and Single-Dose Vaccination: A Prospective Cohort Study.

Investigating antibody titers in individuals who have been both naturally infected with SARS-CoV-2 and vaccinated can provide insight into antibody dynamics and correlates of protection over time. Human coronavirus (HCoV) IgG antibodies were measured longitudinally in a prospective cohort of qPCR-confirmed, COVID-19 recovered individuals (k = 57) in British Columbia pre- and post-vaccination. SARS-CoV-2 and endemic HCoV antibodies were measured in serum collected between Nov. 2020 and Sept. 2021 (n = 341). Primary analysis used a linear mixed-effects model to understand the effect of single dose vaccination on antibody concentrations adjusting for biological sex, age, time from infection and vaccination. Secondary analysis investigated the cumulative incidence of high SARS-CoV-2 anti-spike IgG seroreactivity equal to or greater than 5.5 log10 AU/mL up to 105 days post-vaccination. No re-infections were detected in vaccinated participants, post-vaccination by qPCR performed on self-collected nasopharyngeal specimens. Bivariate analysis (complete data for 42 participants, 270 samples over 472 days) found SARS-CoV-2 spike and RBD antibodies increased 14-56 days post-vaccination (p < 0.001) and vaccination prevented waning (regression coefficient, B = 1.66 [95%CI: 1.45-3.46]); while decline of nucleocapsid antibodies over time was observed (regression coefficient, B = -0.24 [95%CI: -1.2-(-0.12)]). A positive association was found between COVID-19 vaccination and endemic human β-coronavirus IgG titer 14-56 days post vaccination (OC43, p = 0.02 & HKU1, p = 0.02). On average, SARS-CoV-2 anti-spike IgG concentration increased in participants who received one vaccine dose by 2.06 log10 AU/mL (95%CI: 1.45-3.46) adjusting for age, biological sex, and time since infection. Cumulative incidence of high SARS-CoV-2 spike antibodies (>5.5 log10 AU/mL) was 83% greater in vaccinated compared to unvaccinated individuals. Our study confirms that vaccination post-SARS-CoV-2 infection provides multiple benefits, such as increasing anti-spike IgG titers and preventing decay up to 85 days post-vaccination.

Plaque-neutralizing antibody to BA.2.12.1, BA.4 and BA.5 in individuals with three doses of BioNTech or CoronaVac vaccines, natural infection and breakthrough infection.

BackgroundBA.2.12.1, BA.4 and BA.5 subvariants of SARS-CoV-2 variant-of-concern (VOC) Omicron (B.1.1.529) are spreading globally. They demonstrate higher transmissibility and immune escape.ObjectivesDetermine BA.2.12.1, BA.4 and BA.5 virus plaque reduction neutralization test (PRNT) antibody titres in individuals recently vaccinated with BNT162b2 (n = 20) or CoronaVac (n = 20) vaccines or those convalescent from ancestral wild- type (WT) SARS-CoV-2 (n = 20) or BA.2 infections with (n = 17) or without (n = 7) prior vaccination.ResultsRelative to neutralization of the WT virus, those vaccinated with BNT162b2 had 4.8, 3.4, 4.6, 11.3 and 15.5-fold reductions of geometric mean antibody titres (GMT) to BA.1, BA.2, BA.2.12.1, BA.4 and BA.5 viruses, respectively. Similarly, those vaccinated with CoronaVac had 8.0, 7.0, 11.8, 12.0 and 12.0 fold GMT reductions and those with two doses of CoronaVac boosted by BNT162b2 had 6.1, 6.7, 6,3, 13.0 and 21.2 fold GMT reductions to these viruses, respectively. Vaccinated individuals with BA.2 breakthrough infections had higher GMT antibody levels vs. BA.4 (36.9) and BA.5 (36.9) than unvaccinated individuals with BA.2 infections (BA.4 GMT 8.2; BA.5 GMT 11.0).ConclusionsBA.4 and BA.5 subvariants were less susceptible to BNT162b2 or CoronaVac vaccine elicited antibody neutralization than subvariants BA.1, BA.2 and BA.2.12.1. Nevertheless, three doses BNT162b2 or booster of BNT162b2 following two doses of CoronaVac elicited detectable BA.4 and BA.5 neutralizing antibody responses while those vaccinated with three doses of CoronaVac largely fail to do so. BA.2 infections in vaccinated individuals led to higher levels of BA.4 or BA.5 neutralizing antibody compared to those who were vaccine-naive.

Thyroid Antibody Titers and Hypothalamic-Pituitary-Thyroid Axis Activity in Levothyroxine-Treated Women With Autoimmune Subclinical Hypothyroidism Receiving Atorvastatin or Metformin.

Both metformin and statins reduce thyroid antibody titers in individuals with Hashimoto thyroiditis. The present study compared the impact of low-grade systemic inflammation and insulin resistance on levothyroxine action in subjects with this disorder. The study included 3 groups of women with autoimmune subclinical hypothyroidism matched for thyroid antibody titers and hormone levels: patients receiving atorvastatin (group A) or metformin (group B) and statin- and metformin-naïve women (group C). Over the entire study period (6 months), all individuals received levothyroxine. Titers of thyroid antibodies, as well as concentrations of thyrotropin, free thyroid hormones, prolactin, lipids, glucose, insulin, high-sensitivity C-reactive protein (hsCRP), and 25-hydroxyvitamin D were assessed at baseline and 6 months later. At baseline, the study groups differed in plasma lipids, insulin sensitivity, and hsCRP. In all groups of patients, levothyroxine decreased thyroid antibody titers, reduced thyrotropin levels and increased free thyroid hormone levels. Treatment-induced changes in antibody titers and free thyroid hormone levels were strongest in group A, while the changes in thyrotropin were most pronounced in group B. The decrease in antibody titers correlated to a greater degree with hsCRP levels than with insulin sensitivity. The obtained results suggest that low-grade systemic inflammation is a more important factor determining the impact of levothyroxine on thyroid autoimmunity and thyroid hormone levels than insulin resistance.

Retention of Neutralizing Response against SARS-CoV-2 Omicron Variant in Sputnik V-Vaccinated Individuals.

The new Omicron variant of SARS-CoV-2, first identified in November 2021, is rapidly spreading all around the world. Omicron has become the dominant variant of SARS-CoV-2. There are many ongoing studies evaluating the effectiveness of existing vaccines. Studies on the neutralizing activity of vaccinated sera against the Omicron variant are currently being carried out in many laboratories. In this study, we have shown the neutralizing activity of sera against the SARS-CoV-2 Omicron variant compared to the reference Wuhan D614G variant in individuals vaccinated with two doses of Sputnik V up to 6 months after vaccination and in individuals who experienced SARS-CoV-2 infection either before or after vaccination. As a control to our study we also measured neutralizing antibody titers in individuals vaccinated with two doses of BNT162b2. The decrease in NtAb titers to the Omicron variant was 8.1-fold for the group of Sputnik V-vaccinated individuals. When the samples were stratified for the time period after vaccination, a 7.6-fold or 8.8-fold decrease in NtAb titers was noticed after up to 3 and 3-to-6 months after vaccination. We observed a 6.7- and 5-fold decrease in Sputnik V-vaccinated individuals experiencing asymptomatic or symptomatic infection, respectively. These results highlight the observation that the decrease in NtAb to the SARS-CoV-2 Omicron variant compared to the Wuhan variant occurs for different COVID-19 vaccines in use, with some showing no neutralization at all, confirming the necessity of a third booster vaccination.

Longevity and Clinical Effectiveness of the Humoral and Cellular Responses to SARS-CoV-2 Vaccination in Hemodialysis Patients

Longevity and Clinical Effectiveness of the Humoral and Cellular Responses to SARS-CoV-2 Vaccination in Hemodialysis Patients

SARS-CoV-2 infection shortly after BNT162b2 vaccination results in high anti-spike antibody levels in nursing home residents and staff.

IntroductionOne dose of a coronavirus disease 2019 (COVID‐19) vaccine can elicit high antibody titers in individuals who were previously infected by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2). However, it is unclear how a SARS‐CoV‐2 infection shortly after a first COVID‐19 vaccine dose affects antibody responses.MethodsHere we investigate residents and staff of a nursing home, where a COVID‐19 outbreak occurred shortly after the first BNT162b2 immunization.Results and ConclusionsOur data show that individuals who got infected as early as 10 days after their first immunization show antibody levels comparable to fully vaccinated individuals.

Quantification of SARS-CoV-2 antibodies with eight commercially available immunoassays.

Since the emergence of SARS-CoV-2 numerous antibody assays have become available, demonstrating different performance characteristics. This study focused on a quantitative correlation between different commercial assays and a neutralization test (NT). Comparative data is needed as a basis for the production of convalescent plasma and potential interpretations COVID-19 immunity.Sera of 100 SARS-CoV-2 convalescent plasma donors were collected and SARS-CoV-2 antibodies were characterized using three different IgG-ELISAs (EUROIMMUN IgG and NCP-IgG ELISA, Wantai ELISA), two CLIA (Elecsys, LIAISON) and two lateral flow tests (MEDsan IgM/IgG-Rapid-Test, Wantai Rapid Test) and subsequently correlated to neutralization titers. The Wantai ELISA and the Elecsys provide the highest sensitivities in this sample (98 and 95 percent respectively). Titers with the best overall quantitative correlation to the NT titer were obtained with the Euroimmun IgG ELISA assay (Rho=0.759) and the Wantai ELISA assay (Rho=0.729).An infection without fever and negative or weakly positive reactions in the Wantai Rapid test were negative predictive factors for NT titers >1:200 (negative predictive value of 92 % and 92 % respectively, combination of both 100 %).The Wantai ELISA titer could be a suitable substitute for NT. An adequate pooling strategy of plasma units additionally could compensate deviations of individual antibody titers.

Is there any association between Serum anti-HSP27 antibody level and the presence of metabolic syndrome; population based case-control study

Abstract Background: Heat shock protein 27 (HSP27) is an intracellular chaperone constitutively expressed in many cell types including cardio myocytes and endothelial cells. Circulating levels of HSP27 and anti-HSP27 antibody are higher in patients with CVD. Anti-HSP27 antibody concentrations were also reported to be increased in atherogenesis. We aimed to evaluate serum anti-HSP27 antibody titers in individuals with, or without, MetS in the MASHAD study cohort with large sample size in 6,568 subjects. Methods: Participants with MetS were identified from MASHAD cohort (n=3358) using the IDF criteria, and the control group were those individuals who did not meet these criteria (n=3210). In-house enzyme-linked immune sorbent assay (ELISA) method was used for measuring Anti-HSP27 antibody levels. The two groups were matched for age, sex and smoking habit. Results: As expected, there were significant differences in height (p= 0.004), waist and hip circumference, weight, BMI, systolic and diastolic blood pressure, TGs, TC, HDL-C, Hs-CRP, glucose, with the presence of diabetes mellitus, hypertension, hyperlipidemia (p&lt;0.001) between the two groups. Serum HSP27 antibody titers did not show significant difference between the groups with and without metabolic syndrome (p= 0.740). Conclusion: In conclusion, our results revealed serum anti-HSP27 antibody titers were not statistically different between individuals with and without MetS. However, it is possible that drug treatment may affect antibody titers and confound our findings in this population sample..

Neutralizing Antibody Responses to Homologous and Heterologous H1 and H3 Influenza A Strains After Vaccination With Inactivated Trivalent Influenza Vaccine Vary With Age and Prior-year Vaccination.

Prior influenza immunity influences the homologous neutralizing antibody responses elicited by inactivated influenza vaccines (IIV), but neutralizing antibody responses to heterologous strains have not been extensively characterized. We analyzed neutralizing antibody titers in individuals aged 1-88 who received the 2009-2010 season IIV before infection by or vaccination against the 2009 pandemic H1N1 virus. Neutralization titers to homologous and heterologous past, recent, and advanced H1 and H3 strains, as well as H2, H5, and H7 strains, were measured using influenza hemagglutinin pseudoviruses. We performed exploratory analyses based on age, prior-year IIV, and prevaccination titer, without controlling for Type I errors. IIV elicited neutralizing antibodies to past and advanced H1 and H3 strains, as well as to an H2 strain in individuals who were likely infected early in life. The neutralization of avian subtype viruses was rare, and there was no imprinting of neutralization responses to novel avian subtype viruses based on the influenza group. Compared to adults, children had higher seroresponse rates to homologous and heterologous strains, and their sera generated larger antigenic distances among strains. Seroresponse rates to homologous and heterologous strains were lower in subjects vaccinated with prior-year IIV, though postimmunization titers were generally high. IIV elicited neutralizing antibodies to heterologous H1 and H3 strains in all ages groups, but titers and seroresponse rates were usually higher in children. Prior-year vaccination with the same strains tended to blunt IIV neutralization responses to all strains in young and old age groups, yet postimmunization titers were high.

Immunogenic and protective efficacy of recombinant protein GtxA-N against Gallibacterium anatis challenge in chickens

Gallibacterium anatis is a major cause of reproductive tract infections in chickens. Here, we aimed to evaluate the efficacy of the recombinant protein GtxA-N at protecting hens, by addressing three objectives; (i) evaluating the antibody response following immunization (ii) scoring and comparing lesions, following challenge with G. anatis, in immunized and non-immunized hens and (iii) investigating if the anti-GtxA-N antibody titre in individual hens correlated with the observed lesions. Two consecutive experiments were performed in hens. In the first experiment hens were immunized with GtxA-N on day 0 and day 14, infected with G. anatis on day 28 and euthanized on day 56. The GtxA-N antibody response was assessed in pooled serum samples throughout the experiment, using an indirect enzyme-linked immunosorbent assay (ELISA). In the second experiment the GtxA-N antibody titres were assessed in individual hens before and after immunization. Subsequently, the hens were inoculated with G. anatis and finally all hens where euthanized and submitted for post mortem examination 48 h after inoculation. Immunization elicited strong antibody responses that lasted at least 8 weeks (P < .0001). The individual antibody titres observed in response to immunization varied considerably among hens (range: 174,100–281,500). Lesion scores following G. anatis infection were significantly lower in immunized hens compared to non-immunized hens (P = .004). Within the immunized group, no correlation was found between the individual antibody titres and the lesion scores. This study clearly demonstrated GtxA-N as a vaccine antigen able of inducing protective immunity against G. anatis.

Serum 25-Hydroxyvitamin D is Positively Associated with Enhanced Pnuemococcal Antibody Titers in Individuals with Atopic Conditions

Serum 25-Hydroxyvitamin D is Positively Associated with Enhanced Pnuemococcal Antibody Titers in Individuals with Atopic Conditions

Immune responses in mice, cattle and horses to a DNA vaccine for vesicular stomatitis

Vesicular stomatitis (VS) virus causes an important clinical disease of cattle and horses in North America. In order for a vaccine to be useful in the control of VS, it must not only protect against disease, but allow ready differentiation of infected and vaccinated animals. In these studies, we evaluated neutralizing antibody responses in outbred mice, calves, and horses that received a DNA vaccine that expressed the glycoprotein (G) gene of VS New Jersey virus. The vaccine elicited antibody titers in individuals from each species, especially when two doses were administered, but the level of neutralizing antibody needed to confer protection is not known. In mice, co-administration of a plasmid that expressed interleukin-2 resulted in a significant, though modest, increase in antibody titers relative to use of the G gene vaccine alone. The effect of co-injecting putative immunostimulatory oligonucleotides was also evaluated. This treatment had no apparent effect in horses and was found to suppress immune responses to the G gene vaccine in mice. If the immune responses obtained in these studies prove to protect cattle and horses from infection with VS virus, DNA vaccination may become a useful tool for control of this disease.

Long-term persistence of anti-HBs after vaccination with a recombinant DNA yeast-derived hepatitis B vaccine: 8-year results

The aim of this study was to evaluate the persistence of antibodies 7 years after hepatitis B booster administration in healthy adult volunteers who were vaccinated in 1987. In October 1986, 188 seronegative, healthy adult volunteers (117 men and 71 women) were vaccinated with a 20 μg dose recombinant DNA yeast-derived hepatitis B vaccine. Mean age of the study group was 23.3 years (±0.28). Immunisation was carried out according to a 0-1-2 month vaccination schedule, with a boosterdose at 12 months. Of the 159 subjects who received the full vaccination course, 63 (40%) had a blood sample taken 8 years after the first vaccination. Of these 63 subjects, five were excluded from teh analysis due to an irregular vaccination schedule and four subjects did not complete the accompanying questionnaire on possible booster administration. So, 54 subjects remained available for further analysis. Fourteen individuals had received an additional booster of hepatitis B vaccine sometime between 1989 and 1994. The geometric mean titre (GMT) at month 13 for these 14 individuals was 1494 mIU ml −1, compared with 3103 mIU ml −1 for those who did not receive an interim booster. Forty subjects, who received no additional booster dose besides that of month 12, met the inclusion criteria of the follow-up study. Of these, all subjects except one were seropositive for anti-HBs at month 96 (GMT: 215.9 mIU ml −1). All subjects were still anti-HBc negative at that time. Distribution of individual antibody titres revealed that overall 92.5% of subjects retained protective antibody levels (⩾10 mIU ml −1); 72.5% of vaccinees retained high levels of anti-HBs (⩾100 mIU ml −1) as compared to 99.2 and 97.0% at month 13, respectively. A positive correlation was found between the subjects' titres at month 13 and month 96. A 0-1-2 dose vaccination course with a booster dose administered at month 12, induces a protective immune response which lasts at least until 7 years after the full vaccination course of the subjects. A positive correlation was found between the anti-HBs antibody titres at month 13 and month 96.

Genetics of immunological tolerance: I. Bidirectional selective breeding of mice for oral tolerance

The polygenic nature of oral tolerance regulation was elucidated by the method of bidirectional selective breeding of mouse strains for tolerance susceptibility (TS) and resistance (TR) starting from a genetically heterogeneous population achieved by the equilibrated intercrossing of eight inbred mouse strains (A/J, DBA/2J, P/J, SWR/J, SJL/J, CBA/J, BALB/cJ and C57BL/6J). Seven days after intragastric administration of 5 mg OVA or BSA, mice were intraperitoneally immunized with 100 microg of the corresponding antigen. The individual antibody titres were measured by haemagglutination. The phenotypes at the highest and lowest extremes were selected for assortative mating, avoiding consanguinity. The second litter of each mating couple was intraperitoneally immunized only to evaluate the immunocompetence of the corresponding generation and to ascertain the non-selection of non-responder mice. A normal distribution of agglutinin titres ranging from 4 to 14 log2 was observed in the F0 population. In the F12 generation, TR and TS strains showed highly significant differences for agglutinin titres (TR=15.06+/-1.80 and TS=8.35+/-2.44), and IgG responses by ELISA. Up to the F12 generation, the mean realized heritability was 0.14+/-0.02. The response to the selection was 0.43 log2 and the selection differential 3.10 log2/generation. A provisional estimation indicated that oral tolerance may be influenced by eight or nine independent loci.

Antibody response after treatment in cattle infected with Psoroptes ovis

The decline of anti- Psoroptes ovis antibody titres after treatment was studied in six groups of naturally infected cattle. In all trials, using a limiting dilution technique, the specific antibody levels were assessed by ELISA on sera collected at regular intervals up to 78 days post treatment. All individual antibody titres started to decline between day 7 and day 14 post treatment. A linear decrease was observed. In a limited trial, five experimentally infected animals were bled monthly after treatment and seronegativity was reached within four months. The results obtained Were in agreement with those obtained in the five field trials. Using a linear regression model, it was estimated by interpolation that most of the animals Would have been seronegative Within seven months post treatment. These results suggest that the exposure to specific P ovis antigen stops with the end of parasite activity and that dead mites are relatively non-immunogenic.