Influenza remains one of the most contagious infectious diseases. Approximately, 25-50 million people suffer from influenza-like illness in the United States annually, leading to almost 1 million hospitalizations. Globally, the World Health Organization (WHO) estimates 250,000-500,000 mortalities associated with secondary respiratory complications due to influenza virus infection every year. Currently, seasonal vaccination represents the best countermeasure to prevent influenza virus spread and transmission in the general population. However, presently licensed influenza vaccines are about 60% effective on average, and their effectiveness varies from season to season and among age groups, as well as between different influenza subtypes within a single season. The hemagglutination inhibition (HAI) assay represents the gold standard method for measuring the functional antibody response elicited following standard-of-care vaccination, along with evaluating the efficacy of under-development influenza vaccines in both animal models and clinical trial settings. However, using the classical HAI approach it is not possible to dissect the complexities of variable epitope recognition within a polyclonal antibody response. In this communication, we describe a straightforward competitive HAI-based method using a combination of influenza virus and recombinant hemagglutinin (HA) proteins to dissect the HAI functional activity of HA-specific antibody populations in a single assay format.
Importance:
The hemagglutination inhibition (HAI) assay is a well-established and reproducible method that quantifies functional antibody activity against influenza viruses and in particular the capability of an antibody formulation to inhibit the binding of HA to sialic acid. However, the HAI assay does not provide with full insights on the breadth and epitope recognition of the antibody formulation, especially in the context of polyclonal sera where multiple antibody specificities contribute to the overall observed functional activity.
In this report we introduce the use of Y98F point-mutated recombinant HA (HAΔSA) proteins, which lack sialic acid binding activity, in the context of the HAI assay as a mean to absorb out certain HA-directed (i.e., strain-specific or cross-reactive) antibody populations. This modification to the classical HAI assay, referred to as the competitive HAI assay, represents a new tool to dissect the magnitude and breadth of polyclonal antibodies elicited through vaccination or natural infection.
Comparison of Complement Fixation and Hemagglutination Inhibition Assays for Detecting Antibody Responses following Influenza Virus Vaccination
