Human Antibody Responses to Avian Influenza A(H7N9) Virus, 2013

Understanding host antibody response is crucial for predicting disease severity and for vaccine development. We investigated antibody responses against influenza A(H7N9) virus in 48 serum samples from 21 patients, including paired samples from 15 patients. IgG against subtype H7 and neutralizing antibodies (NAbs) were not detected in acute-phase samples, but ELISA geometric mean titers increased in convalescent-phase samples; NAb titers were 20–80 (geometric mean titer 40). Avidity to IgG against subtype H7 was significantly lower than that against H1 and H3. IgG against H3 was boosted after infection with influenza A(H7N9) virus, and its level in acute-phase samples correlated with that against H7 in convalescent-phase samples. A correlation was also found between hemagglutinin inhibition and NAb titers and between hemagglutinin inhibition and IgG titers against H7. Because of the relatively weak protective antibody response to influenza A(H7N9), multiple vaccinations might be needed to achieve protective immunity.     

Serum IgG titres,but not avidity,correlates with neutralizing antibody response after H5N1 vaccination

Background

Influenza H5N1 virus constitutes a pandemic threat and development of effective H5N1 vaccines is a global priority. Anti-influenza antibodies directed towards the haemagglutinin (HA) define a correlate of protection. Both antibody concentration and avidity may be important for virus neutralization and resolving influenza disease.

Methods

We conducted a phase I clinical trial of a virosomal H5N1 vaccine adjuvanted with the immunostimulating complex Matrix M™. Sixty adults were intramuscularly immunized with two vaccine doses (21 days apart) of 30 μg HA alone or 1.5, 7.5 or 30 μg HA adjuvanted with Matrix M™. Serum H5 HA1-specific antibodies and virus neutralization were determined at days 0, 21, 42, 180 and 360 and long-term memory B cells at day 360 post-vaccination. The binding of the HA specific antibodies was measured by avidity NaSCN-elution ELISA and surface plasmon resonance (SPR).

Results

The H5 HA1-specific IgG response peaked after the second dose (day 42), was dominated by IgG1 and IgG3 and was highest in the adjuvanted vaccine groups. IgG titres correlated significantly with virus neutralization at all time points (Spearman r ≥ 0.66, p < 0.0001). By elution ELISA, serum antibody avidity was highest at days 180 and 360 post vaccination and did not correlate with virus neutralization. Long-lasting H5 HA1-specific memory B cells produced high IgG antibody avidity similar to serum IgG.

Conclusions

Maturation of serum antibody avidity continued up to day 360 after influenza H5N1 vaccination. Virus neutralization correlated with serum H5 HA1-specific IgG antibody concentrations and not antibody avidity.     

Age-related differences in antibody avidities to pertussis toxin and filamentous hemagglutinin in a healthy Japanese population

To gain insights into the current Japanese pertussis immunization schedule, we examined the distributions of antibody titers and avidities to pertussis toxin (PT) and filamentous hemagglutinin (FHA) in 460 Japanese healthy subjects (aged 1–60?years) based on age category. Our avidity enzyme-linked immunosorbent assays revealed that young children aged 1–2?years, which corresponded to ages after receiving primary and/or booster pertussis vaccinations, had relatively high-avidity anti-PT IgG (mean avidity index [AI], 40.5%) compared with other age groups (AI, 26.5–31.9%); however, they had relatively low-avidity anti-FHA IgG (AI, 41.8%). In contrast, children aged 3–6?years had both low-avidity anti-PT IgG (AI, 26.5%) and low-avidity anti-FHA IgG (AI, 40.4%). A significant age-related difference in anti-PT IgG avidity was observed between children aged 1–2?years and 3–6?years (P?<?0.05); however, the difference in anti-FHA IgG avidity was not significant. The anti-PT IgG avidity was positively correlated with the antibody titer, especially among children aged 1–15?years (r_s?=?0.508–0.685; P?<?0.01), indicating that the avidity of vaccine-induced anti-PT IgG decreases with decreasing IgG antibody titer to PT. Our findings strongly suggest that vaccine-induced anti-PT IgG avidity rapidly wanes after vaccination, but this is not observed for anti-FHA IgG avidity. Because children aged 3–6?years have both low-quantity and low-quality antibodies against PT, an additional booster vaccination with acellular pertussis vaccines is required for such children in Japan.     

Quantitative theories of T-cell responsiveness

Summary:  We review recent advances toward a comprehensive mathematical theory of T-cell immunity. A key insight is that the efficacy of the T-cell response is best analyzed in terms of T-cell receptor (TCR) avidity and the distribution of this avidity across the TCR repertoire (the 'avidity spectrum'). Modification of this avidity spectrum by a wide range of tuning and tolerance mechanisms allows the system to adapt cross-reactivity and specificity to the challenge at hand while avoiding inappropriate responses against non-pathogenic cells and tissues. Theoretical models relate molecular kinetic parameters and cellular properties to systemic level statistics such as avidity spectra. Such bridge equations are crucial for rational clinical manipulation of T cells at the molecular level.     

Avidity of antibody responses to Actinobacillus actinomycetemcomitans in periodontitis.

We designed a study to examine the serum IgG antibody avidity characteristics in: (i) normal subjects (N); (ii) Actinobacillus actinomycetemcomitans-infected adult periodontitis (AP Aa+); (iii) A. actinomycetemcomitans-infected localized juvenile periodontitis (LJP Aa+); and (iv) AP subjects (AP) with various antibody patterns and disease presentation. Although there were significant elevations in antibody levels for AP Aa+ and LJP Aa+ patients compared with AP and normal patients (P < 0.0001), there were no significant differences in the avidity indices (AI). Correlations of antibody levels to avidity revealed that functional activity of the antibody as measured by avidity was independent of antibody levels. Increasing antibody levels correlated with an increase in the number of infected sites, yet there was a trend for A1 to decrease with increased infection. Avidity indices for all patient groups did not appear to show a strong biologic relationship to plaque; however, in AP Aa+ and LJP Aa+ patients there was a generally positive relationship between avidity and bleeding on probing or pocket depth. In AP Aa+ and LJP Aa+ patients, and in AP patients there was a positive relationship of avidity through a threshold of approximately 8 active disease sites. This study hypothesized that antibody avidity to A. actinomycetemcomitans could help to explain the relationship between the active host response and chronic infection with this pathogen. The results provide evidence that both antibody levels and avidity may contribute to the variation in host resistance to infection and disease associated with A. actinomycetemcomitans.     

Influence of pH on the detection of low- and high-avidity anti-dsDNA

In 2 radioimmunoassays in use to detect antibodies to dsDNA, the Farr assay and the PEG assay, we observed inhibitory effects of normal human serum (NHS) on the DNA binding by SLE sera. This was found to be due by the fact that, during incubation at 37 degrees C, CO2, introduced in the incubation mixture by the serum, evaporates from the mixture. This results in increase in pH to values well above pH 8.0, which in turn leads to a decreased DNA binding by antibody. When SLE sera are tested at low dilution, this phenomenon may lead to false negative results. Proper pH control, by the use of buffers with a greater buffering capacity than PBS, completely prevented the observed inhibitory effects. However, under these conditions NHS bound significant amounts of DNA in both assays. The non-specific DNA binding by NHS was found to be heat-stable, but could be eliminated either by aerosil treatment of the sera or by addition of dextran sulphate to the incubation mixture. Lipoproteins and, to a lesser extent, the complement component C1q appear responsible for this non-specific binding. To avoid false negative results with SLE sera as well as non-specific binding by NHS, we propose the use of stronger buffers in combination with added dextran sulphate to the incubation mixture in both the Farr assay and the PEG assay.     

Evolution of Anti-RBD IgG Avidity following SARS-CoV-2 Infection

SARS-CoV-2 infection rapidly elicits anti-Spike antibodies whose quantity in plasma gradually declines upon resolution of symptoms. This decline is part of the evolution of an immune response leading to B cell differentiation into short-lived antibody-secreting cells or resting memory B cells. At the same time, the ongoing class switch and antibody maturation processes occurring in germinal centers lead to the selection of B cell clones secreting antibodies with higher affinity for their cognate antigen, thereby improving their functional activity. To determine whether the decline in SARS-CoV-2 antibodies is paralleled with an increase in avidity of the anti-viral antibodies produced, we developed a simple assay to measure the avidity of anti-receptor binding domain (RBD) IgG elicited by SARS-CoV-2 infection. We longitudinally followed a cohort of 29 convalescent donors with blood samples collected between 6- and 32-weeks post-symptoms onset. We observed that, while the level of antibodies declines over time, the anti-RBD avidity progressively increases and correlates with the B cell class switch. Additionally, we observed that anti-RBD avidity increased similarly after SARS-CoV-2 mRNA vaccination and after SARS-CoV-2 infection. Our results suggest that anti-RBD IgG avidity determination could be a surrogate assay for antibody affinity maturation and, thus, suitable for studying humoral responses elicited by natural infection and/or vaccination.     

Cytomegalovirus antibody avidity in allogeneic bone marrow recipients: Evidence for primary or secondary humoral responses depending on donor immune status

The reconstitution of the human cytomegalovirus (CMV) antibody response in CMV seropositive bone marrow transplant patients was investigated by comparing 11 patients whose donors were CMV seropositive with 8 whose donors were CMV seronegative. Evidence for primary or secondary responses to CMV was sought by determining IgG antibody avidity using an avidity index method, and antibody titre over a period of up to 3 years after transplant. For the patients whose donors were CMV seropositive, the results showed the characteristics of a secondary response, i.e., rising antibody titres of high avidity immediately after transplant. In contrast, the patients with CMV seronegative donors showed evidence of a primary antibody response usually occurring at about 250 days after transplant, i.e., rising antibody levels initially of low avidity maturing to high avidity over the following 100 to 200 days. It is concluded that a secondary response and hence transfer of humoral immunity had occurred in those patients whose donor was CMV seropositive, whereas a delayed primary response occurred in those patients whose donor was CMV seronegative. © 1996 Wiley-Liss, Inc.     

Avidity of Aspergillus umbrosus IgG antibodies in farmer's lung disease.

Farmer's lung disease (FL), the commonest form of allergic alveolitis caused by repeated inhalation of mouldy hay, is associated with exposure to the fungus Aspergillus umbrosus among Finnish farmers. The antigen-binding avidity of A. umbrosus-specific IgG antibodies was measured in 12 FL patients in acute phases of initial and recurrent attacks and during 1 year follow up as well as in 12 healthy farmers and five healthy urban controls. The farmers' groups were further divided into two subgroups: subjects with short exposure (< 7 years) and subjects with long exposure (> 25 years). During the first acute phase FL patients with long exposure exhibited a high avidity of A. umbrosus-specific IgG antibodies that remained high during the 1 year follow up, although the A. umbrosus-specific IgG antibody titre decreased. A re-exposure to mouldy hay leading to a recurrence further enhanced the maturation of the antibody avidity, so that an even higher A. umbrosus-specific IgG avidity with a less significant increase of antibody titre occurred than during the first acute attack. Notably higher IgG antibody avidity was observed in FL patients with long exposure than in healthy farmers or in healthy controls.     

Evaluation of protein-denaturing immunoassays for avidity of immunoglobulin G to rubella virus

Immunoassays have been recently developed that measure the avidity of IgG antibodies to complex microbial antigens and are suitable for serologic diagnosis of infectious diseases. In these avidity ELISAs, proteindenaturing agents are applied either as diluents of patient sera to prevent the immune complexing of IgG (diluting principle), or the preformed complexes are treated with the protein denaturants (eluting principle). We compared four protein denaturants previously used in such assays, in a diagnostic avidity ELISA for rubella IgG. Diethylamine, guanidine, thiocyanate, or urea were applied, by either principle at various concentrations, and thiocyanate, or urea were applied, by either principle at various concentrations, and thiocyanate at an optimum pH. Patient sera obtained recently after primary infection were distinguished from sera representing past rubella immunity by any protein denaturant tested by the eluting principle, which was superior to the diluting principle. © 1994 Wiley-Liss, Inc.