CHI3L1 and infection: Kamle et al. [23] demonstrated that CHI3L1 increased the expression of ACE2 and SPP in epithelial cells by studying typical delta (δ)- and omicron (ο)-variant mutations of the virus, leading to the uptake of pseudo-viruses expressing alpha, beta, gamma, delta, or omicron S proteins by epithelial cells, thereby enhancing their infection.