LIF and COVID-19: Among the seven risk-increasing proteins, Interleukin-10 (IL-10) Receptor subunit β, FGF-19, and CCL-2 were positively and causally contributing to both hospitalized COVID-19 and critical COVID-19 (OR: 1.10~1.16), while eukaryotic translation initiation factor 4E binding protein 1 (EIF4EBP1), IL-7, Neurotrophin-3 (NTF3), and Leukemia Inhibitory Factor (LIF) served as causal risk factors for critical COVID-19 only (OR: 1.07~1.16).