Visceral adipose macrophage content does not associate with body mass index or systemic inflammation in COVID-19: an autopsy study

IntroductionAdiposity, especially visceral adiposity with elevated body mass index (BMI), is associated with a hyperinflammatory syndrome and poor outcomes in patients with COVID-19. In other diseases such as obesity, type 2 diabetes, and rheumatoid arthritis, systemic inflammation is driven directly by visceral adipose macrophages which release pro-inflammatory cytokines. Currently it is unknown whether visceral adipose tissue macrophage content may similarly explain the observation that COVID-19 patients with elevated BMI are at risk for a hyperinflammatory syndrome and death. MethodsThis was a retrospective study of hospitalized adults who died of COVID-19 between March 2020 and June 2020 and underwent autopsy. Visceral adipose tissue macrophage content was quantified by histological staining of visceral adipose tissue samples with CD68, using pericolic fat gathered at autopsy from each subject. Clinical data including inflammatory markers such as erythrocyte sedimentation rate (ESR), C-reactive Protein (CRP), Troponin, D-dimer, Interleukin-6 (IL-6), and ferritin as well as BMI were collected from electronic medical records. ResultsA total of 39 subjects were included in this study. There was no association between BMI and visceral adipose tissue macrophage content (Spearman R=0.025, p=0.88). Additionally, there was no association between adipose tissue macrophage content and any of the systemic markers of inflammation measured including ESR, CRP, Troponin, D-dimer, IL-6, and Ferritin (p>0.05 for all markers). ConclusionUnlike chronic diseases such as obesity, type 2 diabetes, and rheumatoid arthritis, elevated BMI is not associated with increased visceral adipose tissue macrophage content in patients who died of COVID-19. Additionally, among patients who died of COVID-19, visceral adipose tissue macrophage content is not associated with markers of systemic inflammation. These results suggest that the elevations in systemic markers of inflammation--and the hyperinflammatory syndrome often observed during acute COVID-19--does not directly originate from visceral adipose macrophages as it seems to in chronic disease states.