Many individuals carry low‑affinity self‑reactive

lymphocytes that escape deletion but remain functionally silent under normal

conditions due to intact immune tolerance mechanisms. Epidemiological studies

show that autoimmune diseases often arise after infections, tissue injury, or

chronic inflammation—even in individuals without identifiable monogenic defects

in immune regulation. In many cases, disease persists long after the initiating

inflammatory event has resolved.

What is the most plausible explanation for how inflammatory

environments contribute to the initiation of autoimmune disease?

Two individuals with similar environmental

exposures—including prior infection and comparable inflammatory

histories—develop autoimmune disease. One develops systemic lupus erythematosus

with immune complex deposition and interferon‑driven pathology affecting

multiple organs. The other develops rheumatoid arthritis characterised by

chronic synovial inflammation and joint‑restricted damage.

After antigen activation, B cells enter germinal centres

where they undergo rapid proliferation accompanied by somatic hypermutation.

Many of these mutations reduce antigen binding, while others improve it. Only B

cells receiving sufficient survival signals are selected to persist and

differentiate, while the remainder undergo apoptosis.

The SARS-CoV-2 Omicron variant rapidly became the dominant

strain worldwide. Compared to earlier variants, it carries numerous mutations

in the spike protein, affecting both viral entry and recognition by the immune

system.

Which of the following best explains a key factor

contributing to Omicron’s rapid spread?

SARS-CoV and SARS-CoV-2 (COVID-19) are related coronaviruses

that both infect human cells by binding to the ACE2 receptor. However,

SARS-CoV-2 has additional features in its spike protein that influence how

efficiently it enters host cells and spreads between people.

Which of the following best explains a major molecular

difference between SARS-CoV and SARS-CoV-2?

Although the 2009 H1N1 influenza virus was novel, many

infected individuals experienced mild illness, and overall mortality was lower

than initially predicted.

Which factor most plausibly contributed to this relatively

limited clinical impact?

Some avian influenza viruses can infect humans and cause

severe disease, yet sustained human‑to‑human transmission is rare.

Nonetheless, health agencies closely monitor these viruses for pandemic

potential.

Why are certain avian influenza strains regarded as

potential future pandemic threats?

Studies of lung tissue from patients with SARS-CoV-2

infection have revealed patterns in the host immune response that correlate

with disease severity. In severe COVID-19, dysregulation of certain immune

pathways contributes to lung injury.

Which statement best explains the molecular basis of lung

damage in severe COVID-19 cases?

For influenza virus infection to proceed, the viral envelope

must fuse with the host cell membrane following receptor attachment. This

process depends on precise structural rearrangements of the haemagglutinin

protein.

During the early 20th century influenza pandemic, certain

viral strains adapted to humans by altering their preference for host cell

receptors. These changes affected both viral replication sites and transmission

efficiency.

Which viral adaptation would most plausibly explain

increased population‑level spread during human adaptation?