Protocol for iterative indirect immunofluorescence imaging of frozen mouse intestinal tissues

Here, we present a protocol for iterative indirect immunofluorescence imaging (4i) of frozen tissues (Cryo-4i). We describe the steps for mouse intestinal sample preparation and antibody elution with standard reagents. Avoiding antibody conjugation or specialized equipment makes this protocol cost-effective and accessible. It requires two days for setup and one day per imaging round; five rounds allow multiplexed detection of 10 markers in a single section. We also detail procedures for using a MATLAB-based pipeline which enables quantitative single-cell analysis.