Figure 5. A dysregulated circulating baseline T cell phenotype is associated with severe disease in the setting of high viral loads upon infection.

Age-matched female CC-RIX were infected intranasally with SARS-CoV MA15 and mice were monitored for death, weight loss, and lung viral loads. To identify possible baseline immune predictors of disease upon infection with a high early lung viral load, we classified CC-RIX lines with extreme phenotypes based on both lung viral loads at days 2 and 4 post-infection, as well as weight loss and mortality. Lines were categorized as “no disease high titer” (NDHT), which had 0–5% weight loss upon infection and no death despite day 2 average lung viral titers of >10⁷ and average day 4 lung viral titers of >10⁵ (N=3 lines) and “disease high titer” (DHT; N=3 lines) if they experienced greater than 15% weight loss and death, as well as average lung viral titers at day 2 post-infection of >10⁷ and average lung viral titers at day 4 post-infection of >10⁵. Lung viral titers from these 6 CC-RIX lines are shown for days 2 and 4 post-infection (A). Mice from a second cohort of 3–6 age-matched male mice of these selected 6 lines were euthanized and splenic cells analyzed by flow cytometry staining to determine the CD4:CD8 ratio (B), % of CD4 T cells that are CD25+ (C), % of CD8 T cells that are CCR5+ (D), % of Tregs that are CD25+ (E), and % of Tregs that are CTLA-4+ (F). In addition, splenic cells were treated with anti-CD3/CD28 for intracellular cytokine staining assessment of (G) %TNF+IFNg+ of CD8 T cells. Statistical significance was determined by Mann-Whitney test. (H–J) Heat maps were made to compare the average percent of the indicated cell populations. No statistical significance (p>0.05 by Mann-Whitney test) was found for any comparisons except those indicated in Figures 5B–G.