Karissa Fryar1, Nathan Conrad1, Ben Lee2, Matthew Kuennen1. 1High Point University, High Point, NC. 2Coventry University, Coventry, United Kingdom.

BACKGROUND: Data from animal models suggest that some forms of viral infection can increase risk for exertional heatstroke (EHS), possibly via reductions in immunocompetence. This study examined immunocompetence in persons with prior clinical diagnosis of SARS-CoV-2 infection, who were challenged with 60min of cycling exercise in hot, dry ambient conditions. METHODS: Eighteen participants (Age: 21 ± 1 years, Stature: 1.7±0.1 m, Mass: 70.3±2.7 kg, VO2max: 47±2 mL-1kg lean body mass-1.min-1) completed 1hr of cycling exercise in an environmental chamber (35°C/35% RH) at an intensity that elicited 9.0 W/kg of metabolic heat production. Ten participants had been previously diagnosed with SARS-CoV-2, and the other eight participants served as Control. Blood samples collected before (Pre), after (Post), 1h after (1-Post), and 3h after (3-Post) exercise, were assayed for soluble cluster of differentiation 14 (sCD-14), soluble intercellular adhesion molecule 1 (sICAM-1), interferon gamma (IFN-y), and interleukin 8 (IL-8). Heart rate (HR), esophageal temperature (Tc), mean body temperature (Tb), minute ventilation (VE), and oxygen consumption (VO2) were also measured throughout exercise. Between-group differences were examined using RM-ANOVA with Bonferroni Post Hocs. RESULTS: Persons with prior SARS-Cov-2 infection exhibited elevated plasma concentrations of sCD-14 at Pre, Post, 1-Post, and 3-Post (Range: 8.2-17.1%; all p<0.05). They also exhibited elevated IFN-y concentrations at 1-Post exercise (59.6±11pg/ml; p<0.05). Plasma IL-8 and sICAM-1 concentrations were not different between groups [both p>0.05] and as compared to Control, persons with prior SARS-CoV-2 infection did not exhibit greater elevations in HR (87±5% vs 82±8% of HRmax), Tc (1.27±0.50 vs 1.25±0.63 °C), Tb (1.21±0.41 vs 1.12±0.47 °C), VE (40.7±7.0 vs 36.8±7.8 L/min) or VO2 (22.9±2.7 vs 24.3±2.4 mL-1kg lean body mass-1.min-1) during the 1hr cycling challenge [all p>0.05]. CONCLUSIONS: IFN-y exhibits direct anti-viral activity and is secreted by activated t-lymphocytes. sCD-14 mediates lipopolysaccharide (LPS) clearance via transport of cell-bound LPS to plasma lipoproteins. Collectively, we interpret the elevated IFN-y and sCD-14 in persons with prior SARS-CoV-2 infection to indicate that immunocompetence was maintained in the hours following exertional heat stress. These data may have additional context in the area(s) of latent infection and viral reactivation, but require further study before definitive statements can be made.

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