GCG and infection: The various effects of DPP-4i are achieved by inhibiting the DPP-4 enzyme, which normally degrades the incretin hormone (GLP-1) [1] (Figure 5) and is involved in the infection and spread of COVID-19 in the host [1], including the proliferation of T cells [22], NF-kB pathway enhancement [49], and thus, increased inflammatory cytokines production [50], B cell activation, and CD86 expression [12].