Prior Sars-Cov-2 Infection Does Not Reduce Immunocompetence In Humans Challenged With Exertional Heat Stress

PURPOSE: Animal models suggest that some forms of viral infection can increase risk for exertional heatstroke (EHS) via reduced immunocompetence. Immunocompetence was examined in persons with prior clinical diagnosis of SARS-CoV-2 infection, who were challenged with 60 min 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-1 kg-1.min-1) completed 1 hr 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. Eight participants served as Control. Blood samples collected before (Pre), after (Post), 1 h after (1-Post), and 3 h 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 and mean body temperatures (Tc & Tb), minute ventilation (VE), and oxygen consumption (VO2) were 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) and elevated IFN-y concentrations at 1-Post exercise (59.6 ± 11 pg/ml; p < 0.05). Plasma IL-8 and sICAM-1 concentrations were not different between groups [both p > 0.05]. When 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 (1.3 ± 0.5 vs 1.3 ± 0.6 °C), Tb (1.2 ± 0.4 vs 1.1 ± 0.5 °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-1 kg-1.min-1) during the 1 hr cycling challenge [all p > 0.05].

CONCLUSIONS: IFN-y is secreted by activated t-lymphocytes and exhibits direct anti-viral activity. sCD-14 mediates lipopolysaccharide (LPS) clearance via transport of cell-bound LPS to plasma lipoproteins. Collectively, elevated IFN-y and sCD-14 in persons with prior SARS-CoV-2 infection indicates 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