Measles virus-specific immunoglobulin G subclass response in serum and cerebrospinal fluid

Assessment of humoral immune responses to blood-stage malaria antigens following ChAd63-MVA immunization, controlled human malaria infection and natural exposure

The development of protective vaccines against many difficult infectious pathogens will necessitate the induction of effective antibody responses. Here we assess humoral immune responses against two antigens from the blood-stage merozoite of the Plasmodium falciparum human malaria parasite--MSP1 and AMA1. These antigens were delivered to healthy malaria-naïve adult volunteers in Phase Ia clinical trials using recombinant replication-deficient viral vectors--ChAd63 to prime the immune response and MVA to boost. In subsequent Phase IIa clinical trials, immunized volunteers underwent controlled human malaria infection (CHMI) with P. falciparum to assess vaccine efficacy, whereby all but one volunteer developed low-density blood-stage parasitemia. Here we assess serum antibody responses against both the MSP1 and AMA1 antigens following i) ChAd63-MVA immunization, ii) immunization and CHMI, and iii) primary malaria exposure in the context of CHMI in unimmunized control volunteers. Responses were also assessed in a cohort of naturally-immune Kenyan adults to provide comparison with those induced by a lifetime of natural malaria exposure. Serum antibody responses against MSP1 and AMA1 were characterized in terms of i) total IgG responses before and after CHMI, ii) responses to allelic variants of MSP1 and AMA1, iii) functional growth inhibitory activity (GIA), iv) IgG avidity, and v) isotype responses (IgG1-4, IgA and IgM). These data provide the first in-depth assessment of the quality of adenovirus-MVA vaccine-induced antibody responses in humans, along with assessment of how these responses are modulated by subsequent low-density parasite exposure. Notable differences were observed in qualitative aspects of the human antibody responses against these malaria antigens depending on the means of their induction and/or exposure of the host to the malaria parasite. Given the continued clinical development of viral vectored vaccines for malaria and a range of other diseases targets, these data should help to guide further immuno-monitoring studies of vaccine-induced human antibody responses.

Phenotypes of allo- and autoimmune antibody responses to FVIII characterized by surface plasmon resonance

Evidence of antibody isotype/subtype switching may provide prognostic value regarding the state of immune responses to therapeutic proteins, e.g. anti-factor VIII (FVIII) antibodies that develop in many hemophilia A patients, clinically termed “inhibitors”. A sensitive, high- information-content surface plasmon resonance (SPR) assay has been developed to quantify IgG subtype distributions and the domain specificity of anti-drug antibodies. Plasma samples from 22 subjects with an allo- or auto-immune reaction to FVIII were analyzed. Pre-analytical treatment protocols were developed to minimize non-specific binding and specific matrix interference due to von Willebrand factor-FVIII interactions. The dynamic range for IgG quantification was 0.2–5 µg/ml (∼1–33 nM), allowing characterization of inhibitor-positive samples. Subtype-specific monoclonal antibodies were used to quantify the IgG subtype distribution of FVIII-specific antibodies. Most samples obtained from multiply-infused inhibitor subjects contained IgG4 antibodies. Several distinct phenotypes were assigned based on the IgG subtype distribution: IgG₁, IgG₄, IgG₁ & IgG₄, and IgG₁, IgG₂ & IgG₄. An IgG₁-only response was found in mild/moderate HA subjects during early FVIII infusions, and analysis of serial samples followed antibody class switching as several subjects’ immune responses developed. Competition studies utilizing a recombinant FVIII-C2 domain indicated 40–80% of FVIII-specific antibodies in most samples were directed against this domain.

Early appearance of neutralizing immunoglobulin G3 antibodies is associated with chikungunya virus clearance and long-term clinical protection

Background. Chikungunya virus (CHIKV) and related arboviruses have been responsible for large epidemic outbreaks with serious economic and social impact. Although infected individuals clear the virus from the blood, some develop debilitating and prolonged arthralgia.

Methods. We investigated specificity and strength of antibody responses in a longitudinal study on CHIKV-infected patients and analyzed their association with viral load, cytokine profile, and severity.

Results. We found that CHIKV-specific response is dominated by immunoglobulin G3 (IgG3) antibodies. The antibodies were neutralizing, and patients with high viremia rapidly developed high levels of anti-CHIKV antibodies of this specific isotype. Although these patients endured a more severe disease progression during the acute viremic phase, they cleared the virus faster and did not experience persistent arthralgia. However, significant persistent arthralgia was observed in patients with low viremia who developed IgG3 at a later stage.

Conclusions. Absence of early CHIKV-specific IgG3 may therefore serve as a specific marker of patients with increased risk of disease.

Immunoglobulin G subclass profile of antimeasles response in vaccinated children and in adults with measles history

The aim of this study was to investigate measles-specific immunoglobulin G (IgG) subclass profile in vaccinated children and in adults with natural infection. Serum samples were collected before and 30 days after vaccination. The sera from 51 late convalescent adults and seven adults with natural measles infection at the 12th day after onset of rash have been also investigated. Measles IgG antibodies and specific IgG subclasses were tested by enzyme-linked immunosorbent techniques. In children younger than 3 years, the predominant subclass was IgG3, which contributed, on average, 63.3% of the total IgG response. The contributions of specific IgG1 and IgG4 to the total IgG antimeasles response were lower (19.9% and 16.8%, respectively), whereas IgG2 was not found. In contrast, in the group of children older than 4 years, just IgG2 was a predominant subclass; it contributed 42.6% of the total IgG response. Other subclasses were also present but the contribution was much lower. In adult volunteers with measles history, IgG2 was a predominant subclass of total IgG. Thus, in early convalescence IgG2 contributed 62% of the total IgG response, whereas in late convalescence the contribution was lower (41.4%). There were no visible differences in IgG subclass composition between subjects with natural infection and vaccinated children except those below 3 years of age. The humoral immune response of such subjects is immature and the IgG2 subclass of virus-specific antibodies has not been revealed in the sera.

Serum antibody responses in children with rotavirus diarrhea can serve as proxy for protection

We examined sera from 42 patients 1 to 30 months of age for rotavirus immunoglobulin M (IgM), IgA, IgG, and IgG subclasses and sought to determine if serum antibody could serve as a reliable marker for prediction of disease severity. Infants in the first few months of life usually had high maternal IgG titers and, when they were infected with rotavirus, had low IgM titers or no IgM in acute-phase sera and poor seroconversions 3 weeks later, suggesting that maternal antibodies had inhibited viral replication and antibody responses. All patients > or =6 months of age had IgM in acute-phase sera, indicating that IgM is a good marker for acute rotavirus infection. IgG was the best overall predictor of an infection, as the convalescent-phase sera of 81% of the patients had a fourfold rise in the IgG titer. IgA titers in convalescent-phase sera and conversion rates were higher among patients > or =12 months of age than among children younger than 12 months. IgG1 was the predominant subclass detected in the acute-phase sera of some children and in all 28 convalescent-phase serum samples examined. Patients with preexisting acute-phase IgG titers of > or =100 or > or =200 had diarrhea that was less severe or of a shorter duration. These results indicate that serum IgG is the most reliable marker for seroconversion and is a consistent proxy for protection against severe disease.

Measles virus protein-specific IgM, IgA, and IgG subclass responses during the acute and convalescent phase of infection

The availability of new generation serological assays allowed re-evaluation of the antibody response to measles virus. IgM, IgA, total IgG, and IgG subclass responses were studied to the three major immunogenic measles virus proteins: the fusion protein (F), haemagglutinin (H), and nucleoprotein (N). Plasma samples were obtained from clinically diagnosed measles cases (n = 146) in Khartoum (Sudan) within a week after onset of the rash. Convalescent phase samples were collected from 32 of 117 laboratory-confirmed measles cases at different time points after onset of rash. Glycoprotein-specific IgM, IgG, and IgA antibody levels correlated well to the N-specific response. For IgG and IgA, responses to F were higher than to H. IgA antibody levels were undetectable in about one third of the laboratory-confirmed cases during the acute phase, but positive in all patients tested 1-4 weeks after infection. IgM levels declined rapidly and were lost 3-6 months after infection. IgA levels declined slowly during the first year but did not return to background levels during the subsequent 2 years. IgG avidity maturation was detected during a 3-6 month period after infection. The predominant IgG subclasses during the acute phase were IgG(1) and IgG(3). The latter was lost in the convalescent phase, while the IgG(4) isotype showed a slight rise afterwards. Interestingly, acute phase IgG(3) and IgA responses were associated, and were only detected in samples with high IgG. This study provides a comprehensive perspective on the antibody response to wild-type measles virus infection.

Neutralizing B cell response in measles

Co-evolving mechanisms of immune clearance and of immune suppression are among the hallmarks of measles. B cells are major targets cells of measles virus (MV) infection. Virus interactions with B cells result both in immune suppression and a vigorous antibody response. Although antibodies fully protect against (re)infection, their importance during the disease and in the presence of a potent cellular response is less well understood. Specific serum IgM appears with onset of rash and confirms clinical diagnosis. After isotype switching, IgG1 develops and confers life-long protection. The most abundant antibodies are specific for the nucleoprotein, but neutralizing and protective antibodies are solely directed against the two surface glycoproteins, the hemagglutinin and the fusion protein. Major neutralizing epitopes have been mapped mainly on the hemagglutinin protein with monoclonal antibodies, producing an increasingly comprehensive map of functional domains.

IgG subclasses in human immune response to wild and attenuated (vaccine) Junin virus infection

Different proportions of IgG subclasses have previously been reported to distinguish the immune response elicited by primary and recurrent viral infections, as well as viral vaccines. The goal of this study was to study the IgG subclasses composition in the immune response of patients with Argentine hemorrhagic fever, and vaccinees with Candid #1 strain of Junin virus. Twenty-four individuals inoculated with Candid #1 vaccine and 67 patients with Argentine hemorrhagic fever were studied. Blood samples were drawn at 30, 60, and/or 180 days post-inoculation with Candid #1 and 30, 60, and 90 days after clinical onset of the disease. Specific anti-Junin virus IgG subclasses were titrated with specific human monoclonal antibody fluorescence isothiocyanate conjugate (FITC) by immunofluorescent assay (IFA). IgG(1) anti-Junin virus was found in every subject studied and IgG(3) was also detected in some patients with a severe form of Argentine hemorrhagic fever. IgG(2) and IgG(4) were not detected in any serum sample studied. The mean titer of specific IgG(1) in vaccinees was significantly lower than in patients with Argentine hemorrhagic fever (P < 0.05), but no difference was found between mild and severe cases of the disease (P > 0.05). The results of this study demonstrated a central role of IgG(1) in human recovery from infection with every strain of Junin virus, an observation stressed by the immune response to Candid #1 vaccine, which resulted in no difference in IgG subclasses composition from that found in mild cases of Argentine hemorrhagic fever.

Measles virus-specific immunoglobulin G isotype immune response in early and late infections

A total of 154 human serum samples (32 acute-phase and 22 convalescent-phase serum samples obtained within a week and between days 8 and 26 after the onset of rash, respectively, and 100 samples drawn from healthy immune adults) were processed by an immunofluorescence assay for the detection of immunoglobulin M (IgM), total immunoglobulin G (IgG), IgG1, IgG2, IgG3, and IgG4 measles virus-specific antibodies. In the acute phase, IgG1 was seen first, followed by IgG2, IgG3, and IgG4 responses, the mean seropositivity of which gradually increased during convalescence, reaching 100% (standard deviation [SD], 84 to 100%), 57% (SD, 34 to 80%), 86% (SD, 66 to 100%), and 86% (SD, 66 to 100%), respectively. IgG2 rose and fell in connection with IgG3 subclass antibodies, showing a rate of detection of IgG2 and/or IgG3 subclass antibodies of 95.5% (range, 100 to 86.5%) in the convalescent phase of infection. The mean percentage of measles IgG2 and IgG3 seropositivity dropped significantly during the memory phase, to 2% (range, 2 to 6%) and 3% (range, 3 to 7%), respectively (P < 0.05); meanwhile IgG1 and IgG4 subclass responses remained relatively unmodified in samples obtained years after infection (mean 100% [SD, 96 to 100%] and 86% [SD, 79 to 93%], respectively). Results obtained defined two highly different immune isotypic response patterns. One pattern is restrictive to IgG2 and/or IgG3 in the convalescent phase and is kinetically similar to the IgM antibody response, so its detection could be referred to as a recent viral activity. On the other hand, IgG1 and IgG4 were detected in both the convalescent and memory phases of the immune response, but their isolated occurrence without IgG2 and IgG3 could be related to the long-lasting immunity.

Seroprevalence of human herpesvirus 6 in Andino Puneños (Argentina)

We carried out a seroepidemiological survey to define the prevalence of human herpesvirus 6 (HHV6) infection in an aboriginal population (Andino Puneños) from a remote region in north-west Argentina. Antibodies against HHV6 (total IgG and the 4 subclasses of IgG) were studied in 84 serum samples (collected in 1995 and stored at -70 degrees C), using core blood mononuclear cells infected with HHV6 in an immunofluorescence assay. Of the 84 samples, 70 (83%; 95% confidence interval, 75-91%) exhibited IgG antibodies against HHV6. No significant differences in the frequency of humoral immunity were found among the 4 age-groups studied (mean ages 13, 31, 47 and 70 years) namely, 75%, 89.7%, 79.2% and 100%, respectively. HHV6-specific IgG1 was found in all the positive serum samples tested but none of them contained specific IgG2, IgG3 and IgG4. These results confirmed a high rate of infection with HHV6 within this aboriginal group in Argentina and an IgG1 anti-HHV6 activity compatible with a maintenance of immunity.