Immunology Lab: Influenza

Influenza A & B nucleic acid

8 single-stranded RNA segments

Influenza A & B nucleoproteins

Coat the RNA, specific to either A or B

Influenza surface glycoproteins

Hemagglutinin (HA) and Neuraminidase (NA)

Function of Hemagglutinin (HA)

Binds to sialic acid on host cells for entry (mainly in upper respiratory tract)

Function of Neuraminidase (NA)

Aids viral entry and exit from host cells

Influenza A naming

Subtype based on HA and NA (e.g., H1N1, H3N2)

Influenza B naming

Lineage-based (e.g., B/Yamagata, B/Victoria)

Lineages of Influenza B

B/Yamagata and B/Victoria

Host range for Influenza A

Can infect multiple species (humans, animals)

Host range for Influenza B

Primarily infects humans

Antigenic shift (reassortment)

Occurs in Influenza A only

Antigenic drift

Occurs in both A and B, but A mutates faster

Influenza A vs B in epidemics

A causes more infections; B increases at end of season

Influenza infection characteristics

Acute; symptoms abrupt, last ~1 week; RNA does not integrate into host genome

Trivalent vaccine

Includes HA from H1N1, H3N2, and 1 B lineage (either Yamagata or Victoria)

Quadrivalent vaccine

Includes HA from H1N1, H3N2, B/Yamagata, and B/Victoria

Annual vaccine types

Egg-based and non-egg-based (for egg allergies)

Flu vaccine versions each year

Two: trivalent or quadrivalent

Test specimen source

Nasopharyngeal/nasal swab in fluid tube

Unknown in the lab test

A nucleoprotein or B nucleoprotein (antigen)

Known in the lab test

Monoclonal anti-influenza antibodies (specific to A or B nucleoproteins)

Antibodies in the test

Some are bound in test regions (A or B), some are unbound in specimen well

Specimen well contents

Unbound antibodies to A and B nucleoproteins (with color conjugate)

Test region A

Bound antibodies specific to A nucleoprotein

Test region B

Bound antibodies specific to B nucleoprotein

Test control region

Always shows a line if the test is valid

Positive result

Control line + A line = Influenza A; Control line + B line = Influenza B

Negative result

Control line only (no A or B lines)

Invalid result

No control line; OR all three lines (Control, A, B) due to rare co-infection/test error

Test principle summary

Antigen-antibody sandwich formation in test region (chicken sandwich model)

Test procedure summary

Swab in fluid tube (15 sec), extract, add 3 drops to specimen well, wait 10 min

Safety protocol for test

Dispose all materials in biohazard

Influenza pandemic risk

Antigenic shift in Influenza A can cause pandemics (e.g., swine flu)

Vaccine coverage trends

Quadrivalent preferred; trivalent used if only one B lineage included

Monoclonal antibodies

Highly specific; do not bind both A and B nucleoproteins

Control region importance

Must appear for test validity

Invalid test (all three lines)

Considered a test malfunction; retest required

Antigen-antibody complex formation

Unbound antibodies (specimen well) + nucleoprotein = colored complex that binds in test region