Influenza-B Antibody

What are the major lineages of Influenza B virus and how do they affect antibody responses?

Influenza B viruses (IBV) are classified into two antigenically distinct lineages: B/Victoria/2/87-like and B/Yamagata/16/88-like lineages. Experimental evidence indicates that vaccination with the B/Yamagata lineage can induce cross-antibody responses to the Victoria lineage, though the reverse is less effective . This asymmetric cross-protection is a critical consideration in vaccine design and immunological studies. Research involving B-cell memory and monoclonal antibodies (mAbs) derived from individuals vaccinated with quadrivalent seasonal vaccines has confirmed the immunological dominance of B/Yamagata hemagglutinin (HA) .

How does the epidemiology of Influenza B virus compare to Influenza A virus?

Influenza B viruses account for approximately 20% of influenza-infected respiratory samples in surveillance data from the United States and Europe . In some seasons, IBV can dominate, contributing to over 50% of influenza cases . Unlike Influenza A, which has an animal reservoir primarily in aquatic birds, IBV infection is almost exclusively restricted to humans, with only rare reports in other species such as seals . The clinical severity of IBV is equivalent to that of Influenza A virus (IAV) , but IBV disproportionately affects children and young adults. Data from Canadian pediatric hospitals showed that the mortality rate among hospitalized patients (aged ≤16 years) with influenza B was higher (1.1%) compared to those with influenza A (0.4%) .

What is the composition of the human antibody repertoire against Influenza B virus?

The serum antibody repertoire against influenza is remarkably restricted and oligoclonal. High-resolution proteomics analysis coupled with high-throughput sequencing of B cell receptor transcripts has shown that the serum repertoire comprises between 40 and 147 distinct antibody clonotypes specific to each monovalent component of the trivalent influenza vaccine . The repertoire is highly polarized, with approximately 6% of the most abundant clonotypes accounting for more than 60% of the entire post-vaccination antibody response . This oligoclonal nature of the antibody response has significant implications for understanding vaccine effectiveness and designing improved immunization strategies.

What are the primary targets of protective antibodies against Influenza B virus?

Protective antibodies against IBV primarily target two surface glycoproteins:

• Hemagglutinin (HA): Many antibodies target the receptor binding domain (RBD) on the HA head, preventing viral attachment to host cells. Some antibodies recognize conserved epitopes in the HA stem region, providing broader protection across different strains .

• Neuraminidase (NA): Human monoclonal antibodies that target IBV NA can display broad and potent capacity to inhibit NA enzymatic activity, neutralize the virus in vitro, and protect against lethal IBV infection in animal models . Some mAbs insert long CDR-H3 loops into the NA active site, engaging highly conserved residues amongst IBV NAs .

The distribution and functionality of these antibodies vary, with some providing strain-specific protection and others offering cross-lineage or broadly reactive protection against multiple IBV strains.

What mechanisms do antibodies employ to protect against Influenza B virus infection?

Antibodies use multiple mechanisms to protect against IBV infection:

• Direct Neutralization: Neutralizing antibodies bind to the virus and prevent its entry into host cells, primarily by targeting the receptor binding domain of HA .

• Inhibition of Viral Release: Anti-neuraminidase antibodies inhibit the enzymatic activity of NA, preventing the release of newly formed virions from infected cells .

• Fc-Mediated Functions: Non-neutralizing antibodies can provide protection through Fc-receptor-mediated effector functions, including antibody-dependent cellular cytotoxicity (ADCC) . Studies have demonstrated that BNA-mAbs display activity in ADCC reporter assays against both B/Yamagata and B/Victoria lineage viruses .

• Prevention of Viral Egress: Some antibodies, such as C12G6, can inhibit IBV via multiple mechanisms, including preventing both viral entry and egress .

Understanding these diverse mechanisms is crucial for designing therapeutic antibodies and vaccines that can provide robust protection against IBV.

How do antibodies exhibit cross-reactivity between the Victoria and Yamagata lineages?

A significant proportion of IBV HA-specific B cells recognize both B/Victoria/2/87-like and B/Yamagata/16/88-like lineages in a distinct pattern of cross-reactivity . Monoclonal antibodies reconstituted from these cross-reactive B cells can provide broad protection in murine models of lethal IBV infection . The cross-reactivity pattern is asymmetric, with B/Yamagata vaccination inducing antibodies that cross-react with B/Victoria antigens more effectively than vice versa .

Cross-reactive antibodies typically target conserved epitopes, including:

• The receptor binding domain (RBD) on the HA head

• The highly conserved HA stem region

• Conserved residues in the NA active site

Understanding the molecular basis of this cross-reactivity is essential for designing broadly protective vaccines and therapeutic antibodies.

What factors influence the co-circulation and lineage dominance of Influenza B viruses?

Multiple factors influence IBV lineage dynamics:

• Age-specific patterns: B/Victoria lineage tends to infect individuals between 10-13 years of age, while B/Yamagata lineage more commonly infects older populations .

• Geographical patterns: In the southern hemisphere, IBV typically peaks 1.1 months later than IAV (August to September) .

• Co-circulation: In 27 out of 84 seasons studied, at least 20% co-circulation of both lineages was reported . B/Victoria contributed approximately 70% of the cases in a typical season, while B/Yamagata accounted for 30% .

• Vaccine mismatch: The proportion of B-lineage vaccine mismatch was 42.9% in countries of the northern hemisphere and 54.2% in countries of the southern hemisphere , highlighting the challenge of selecting the appropriate lineage for trivalent vaccines.

These dynamics have led to the development of quadrivalent vaccines that include both lineages, though effectiveness remains variable across seasons.

How can computational methods improve the design of broadly protective Influenza B vaccines?

Computational methods, particularly the Computationally Optimized Broadly Reactive Antigen (COBRA) methodology, have shown promise in developing more effective IBV vaccines. COBRA-designed hemagglutinin (HA) proteins expressed on virus-like particles (VLPs) have demonstrated superior cross-reactivity compared to wild-type HA antigens .

Key findings from research using COBRA methodology include:

• Ferrets vaccinated with B-COBRA HA vaccines developed neutralizing antibodies with high hemagglutination inhibition (HAI) titers against all influenza B viruses regardless of pre-immunization history .

• In contrast, VLPs expressing wild-type IBV HA antigens preferentially boosted titers against viruses from the same lineage, with little-to-no seroprotective antibodies detected in ferrets with mismatched IBV pre-immune infections .

• A single IBV HA developed using COBRA methodology elicited protective broadly-reactive antibodies against both current and future drifted IBVs from both lineages .

This approach represents a significant advancement over traditional vaccine design methods and offers a pathway to overcome the challenges of lineage mismatch in seasonal influenza vaccines.

What techniques can be used to analyze the serum antibody repertoire in response to Influenza B vaccination?

Advanced techniques for analyzing serum antibody repertoires include:

• Ig-seq (high-resolution proteomics analysis of immunoglobulin): This technique allows quantitative determination of the antibody repertoire at the individual clonotype level .

• BCR-seq (high-throughput sequencing of B cell receptor transcripts): When coupled with Ig-seq, this provides comprehensive insight into the dynamics of antibody responses .

• Monoclonal antibody isolation and characterization: Peripheral blood samples from infected or vaccinated individuals can be used to isolate plasmablasts (CD19+ cells) for subsequent single-cell sorting and antibody cloning .

• Functional assays: These include:

  • Enzyme-linked immunospot (ELISpot) assays to measure antibody-secreting cells

  • Plaque reduction neutralization assays (PRNA) to assess neutralizing capacity

  • ADCC reporter assays to evaluate Fc-mediated functions

  • In vivo protection studies in animal models

These techniques have revealed that the influenza-specific repertoire is highly restricted and oligoclonal, with the top 6% of the most abundant clonotypes accounting for more than 60% of the entire post-vaccination repertoire .

How effective are monoclonal antibodies against Influenza B virus in animal models?

Monoclonal antibodies have demonstrated significant protective efficacy in animal models of IBV infection:

• Prophylactic use: Human monoclonal antibodies targeting IBV neuraminidase (BNA-mAbs) conferred 100% survival against B/New York/PV00094/17 (Yamagata lineage) when administered at 5 mg/kg intraperitoneally 2 hours before intranasal virus challenge in mice . Robust protection was maintained even when the dose was reduced to 1 mg/kg .

• Therapeutic use: BNA-mAbs also demonstrated therapeutic efficacy when administered after infection. Treated animals showed significant reductions in lung viral load, with some antibody treatments (e.g., 1G05) resulting in almost two-log decreases in viral load by 3 days post-infection .

• Broadly protective antibodies: Monoclonal antibodies reconstituted from IBV HA-specific B cells provided broad protection in murine models of lethal IBV infection through multiple mechanisms, including neutralization via binding to the receptor binding domain and Fc-mediated functions of non-neutralizing antibodies binding alternative epitopes .

These findings highlight the potential of monoclonal antibodies as both prophylactic and therapeutic agents against IBV infection.

What structural characteristics make antibodies broadly protective against Influenza B virus?

Several structural features contribute to the broad protective capacity of anti-IBV antibodies:

• CDR-H3 loop insertion: Some broadly neutralizing antibodies that target neuraminidase insert long complementarity-determining region 3 of the heavy chain (CDR-H3) loops into the NA active site, engaging highly conserved residues amongst IBV NAs . This interaction mechanism allows them to inhibit enzymatic activity across diverse IBV strains.

• Recognition of conserved epitopes: Broadly protective antibodies typically recognize highly conserved epitopes in:

  • The receptor binding domain of HA

  • The HA stem region

  • The NA active site

• Multimechanistic action: Some antibodies, such as C12G6, inhibit IBV via multiple mechanisms, including preventing viral entry, egress, and hemagglutinin-mediated fusion . This multifunctional capacity enhances their protective efficacy.

• Fc-mediated functions: Even when direct neutralization is limited, some antibodies provide protection through Fc-receptor-mediated effector functions, including antibody-dependent cellular cytotoxicity (ADCC) .

Understanding these structural characteristics can guide the rational design of improved antibody-based therapeutics and vaccines for broad and durable protection against IBV.

What are the major challenges in developing universally effective vaccines against Influenza B virus?

Several challenges complicate the development of universally effective IBV vaccines:

• Lineage co-circulation: The co-circulation of B/Victoria and B/Yamagata lineages presents a challenge for vaccine composition. Despite moving to quadrivalent vaccines that include strains from both lineages, vaccine effectiveness rates continue to be variable and low in many seasons .

• Lineage mismatch: Historical data shows high rates of B-lineage vaccine mismatch (42.9% in the northern hemisphere and 54.2% in the southern hemisphere) , which significantly reduces vaccine effectiveness.

• Antigenic drift: The HA head undergoes rapid mutation, reducing vaccine effectiveness over time. Current vaccines primarily target this variable region .

• Restricted and polarized antibody repertoire: The serum antibody repertoire against influenza is highly restricted (40-147 clonotypes) and polarized (top 6% of clonotypes accounting for >60% of the repertoire) , which may limit the breadth of protection.

• Age-specific responses: Different age groups show varying susceptibility to different IBV lineages , complicating universal vaccine design.

Addressing these challenges requires innovative approaches, including computationally designed antigens, targeting conserved epitopes, and understanding the molecular basis of cross-lineage protection.

How can high-throughput sequencing technologies advance our understanding of antibody responses to Influenza B virus?

High-throughput sequencing technologies offer several avenues to advance our understanding of antibody responses to IBV:

These approaches will be crucial for developing next-generation vaccines and therapeutic antibodies that provide broader and more durable protection against IBV.