Serology

Serological assays measure circulating antibodies that bind to or neutralize a specific antigen

Antibody response curve

Antibody response curve

Antibodies bind to virus

Influenza hemagglutination inhibition (HI) assay

HI titer correlates strongly with protection

HI assay can measure cross-reactivity

Data presented as pairwise maximum inhibitory titers

Data from many HI assays are hard to summarize

Antigenic cartography


Uses multidimensional scaling (MDS) to position viruses in 2D space such that the distances in this space best fit the HI titers.

Cartography exercise: example


Pairwise titers:

Serum A Serum B
Virus A 2560 80
Virus B 160 1280

Cartography exercise: example


Convert to distances, based on 2-fold drops in titer from highest titer in a column.

Serum A Serum B
Virus A 0 4
Virus B 4 0

Cartography exercise: example


Position elements in 2D space so that distances are recapitulated.

Cartography exercise: data


Serum A Serum B Serum C Serum D
Virus A 2560 80 640 320
Virus B 160 1280 160 80
Virus C 320 40 5120 40
Virus D 320 40 80 2560

Antigenic cartography for H3N2 influenza

More detailed analysis of H3N2 viruses from 2000 to 2007

Primitive lineages die out, while advanced lineages persist

Antigenic evolution leads to clade turnover

The WHO has to keep updating vaccine strain to keep up with ongoing evolution

Vaccine strains map to drift events

Original antigenic sin

"Humans vaccinated against influenza produce antibodies against the immunizing antigen, but produce antibodies of higher titer against the antigen that was their first childhood experience of influenza, even if that strain happened to be absent from the vaccine."

Plotting human HI titers through time

Infection transiently raises titers

Vaccination shows a similar effect

Titers increase more to older viruses, not to antigenically matched viruses

OAS mediates protection against distantly related influenza viruses

Imprinting to group 1 (H1) / group 2 (H3) depends on birth year

Imprinting mediates infection by group 1 (H5) / group 2 (H7) viruses