For decades, immunologists have operated on the principle that following a severe systemic infection and its resolution, the adaptive immune system enters a prolonged refractory period during which the same pathogen is unlikely to provoke a full-blown response again, owing to the durable protection conferred by memory T-cells and circulating antibodies. Unexpected clinical data from longitudinal patient registries may force a reconsideration of this tenet, however. According to the bystander-activation hypothesis, memory T-cells generated during a prior infection remain unexpectedly excitable when confronted with molecular signals from entirely unrelated pathogens. Rather than remaining quiescent until re-encountering their cognate antigen, these sentinel cells can be nonspecifically triggered by cytokine surges produced during a subsequent, unrelated infection; even a mild secondary illness may then unleash a disproportionate inflammatory cascade that reactivates the original pathogen's characteristic symptoms or, in some cases, precipitates an autoimmune attack on tissues bearing structurally similar proteins. Although researchers had long regarded such cross-reactive episodes as biologically implausible, the hypothesis has retrospectively clarified the puzzling temporal clustering of autoimmune flare-ups documented after successive viral outbreaks in tertiary care centers in Sweden, South Korea, and Brazil.

1. The author of the passage suggests that clinical registry data may cast doubt on which of the following longstanding immunological principles?

A. Adaptive immune responses are initiated when the body detects the presence of pathogenic organisms.
B. The onset of autoimmune disorders can be forecast with clinically useful reliability.
C. Memory T-cells are readily activated by cytokine signals emanating from unrelated infectious processes.
D. Severe systemic infections are typically followed by a predictable pattern of gradual convalescence.
E. The adaptive immune system, having successfully cleared a pathogen, remains effectively unreactive to that same pathogen for an extended duration.


2. The passage implies that, before the emergence of the bystander-activation hypothesis, most immunologists would have endorsed which of the following views about T-cell behavior following an infection?

Consider each of the choices separately and select all that apply.

A. Cytokine surges generated by a subsequent, unrelated infection are insufficient to provoke a meaningful response from memory T-cells formed during a prior illness.
B. Memory T-cells retain the capacity to be activated by molecular signals originating from pathogens they have not previously encountered.
C. A patient who has recovered from a severe systemic infection is not at elevated risk of suffering a recurrence of that same infection's hallmark symptoms within a matter of months.