Infection with SARS-Cov-2 results in immune defense in which T cells also play a role.  However, this is ambivalent: although the T cells destroy the viruses, they also secrete the messenger IFN-ƴ at the same time, which triggered the increased production of the surface receptors ACE2 on the intestinal mucosa cells.  This virtually invites the SARS-CoV-2 virus to dock - the prerequisite for a cell invasion.

Intestinal organoids: After treatment with interferon-gamma, the nuclei (blue) of the epithelial cells (green) localize at the basal (outer) edge of the organoids. This is accompanied by increased production of the receptor ACE2, which SARS-CoV-2 uses as an entry port into the cells. Photo: Heuberger/Charité

The intestinal organoids had been developed from intestinal biopsies of patients. The scientists first treated the cultured intestinal cells with IFN-γ to simulate the body's immune response. They then infected the organoids with SARS-CoV-2. Using a laser scanning microscope and gene expression analyses, they were able to measure increased ACE2 expression on the organoids' surface.

Original paper:
Julian Heuberger et al (2021). Epithelial response to IFN-γ promotes SARS-CoV-2 infection. EMBO Molecular Medicine, DOI: 10.15252/emmm.202013191

Source:
https://www.charite.de/service/pressemitteilung/artikel/detail/wie_das_immunsystem_sars_cov_2_den_weg_ebnet/