Research Update
August 8, 2021
A story of influenza
Research project at Dana Farber explores impact of IGH polymorphisms on neutralizing Ab responses.
Project Dates: May 2021 - August 2022
Left: HA domains. Right: HA subtypes of influenza A viruses.
In the influenza virus, hemagglutinin, a surface glycoprotein, mediates adsorption of the virus particles to cell surface receptors. Each hemagglutinin monomer molecule consists of a globular head domain on a stem domain.
Influenza viruses are divided into three main types, based on their antigenic differences in the virion core proteins: A, B and C. Influenza A viruses are also classified in 18 subtypes based on their hemagglutinin protein. Those 18 subtypes are further classified into two major groups based on the phylogenetic relationships of HA genes: groups 1 and 2. Those two groups make up two of the four components of the seasonal influenza vaccine.
HA domains and stem-directed responses
There is growing evidence that immunoglobulin polymorphisms may have a critically important role in Ab responses. Previous studies in the Marasco lab by Avnir et. al showed that genetic differences at the Immunoglobulin Heavy Variable 1-69 gene can modulate Ab responses. Three polymorphism groups were classified based on the presence of either a phenylalanine (F) or leucine (L) at amino acid position 54. The research team found a statistically significant difference in neutralizing activity towards the stem domain between the the F/L and L/L groups.
My main research goal for this project was to study whether this polymorphism has an effect on the intensity of the HA-directed neutralizing Ab response before and/or after vaccination. This study could provide additional evidence to understand the impact of IGH polymorphisms on neutralizing Ab responses. Assuming that the Ab response to the head domain remained somewhat constant, my main hypothesis was that the expression from F-alleles would lead to a higher Ab response in general.
Cohort and protocol
To achieve this goal, the lab recruited 156 donors who received the seasonal influenza vaccine. We sequenced the Donors’ Chromosome 14, which codes for the Immunoglobulin heavy chain and is the most polymorphic locus in the human genome. We also drew blood samples at the day of vaccination and 7 and 30 days post vaccination to measure the Ab response.
The measurements were performed using an MSD indirect ELISA assay. The HA proteins were coated on the plate and the antibodies in the donor plasma bound to the HA coated plate. A secondary polyclonal detection antibody was used to measure the amount of binding to the whole HA molecule by each donor’s plasma.
Overview of the cohort and experimental protocol.
Results
Although there was no significant correlation between the polymorphism groups and the Ab response to the full length H1 and H3 hemagglutinins, a negative correlation between the vaccine response and the increasing donor age was found for both strains. Here, the vaccine response is measured as a fold difference between the Ab response before and seven days after vaccination. We also found a positive correlation between the vaccine response to H1 and H3 strains.
Since the work to date was focused on group 1, my initial analysis focused on the group 2 H3 influenza strain. I created Manhattan plots to visualize the Ab responses to the H3 hemagglutinin across the immunoglobulin heavy chain loci. The x axis represents the nucleotide distance from the centromere. The plots show the significance of each single nucleotide polymorphism in driving a different Ab response for donors with different bases on that locus.
Looking at all SNPs across the IgH.
We found a novel significant genetic relationship (shown in red) in response to the H3 hemagglutinin, which has not been reported before. We can also see that there is an increase in significance one week and 30 days after vaccination. Additional work will have to be done to determine the function of the location of the significant SNP loci, which are mostly found in the area surrounding the Immunoglobulin heavy chain 3-30 gene.
Notes
Image credit: Lofano, G., Kumar, A., Finco, O. et al. Front Immunol. 6, 336 (2015). A.J. Little, A. Matthews, M. Oettinger, D.B. Roth, D.G. Schatz. The mechanism of V(D)J recombination. Elsevier (2015), pp. 13-34.
I would like to thank Dr. Marasco, Hanzhong Ke, Matthew Chang, and the Marasco Lab for giving me this opportunity and for their guidance throughout this project.