DPP4 and obesity disorder: Sarver and Wong (2021) showed that obesity increases the expression of TMPRSS2 and DPP4 with alteration of the ACE/ACE2 ratio. Thereby, obesity may increase the risk of SARS-CoV-2 infection and abnormal immune response by underlying high pro-inflammatory cytokines (Seidu et al., 2021). Therefore, testosterone’s harmful effects in COVID-19 are related to TMPRSS2, ATR1, CD147, DPP4, and AngII expression that are mutually interrelated in facilitating SARS-CoV-2 entry and associated inflammatory reactions (Table 2 and Figure 3).