Figure 1.

Whole-mount immunostaining of M cells in FAE of a PP (Left) and a cecal patch (Right). M cells were classified into two populations based on the expression of the molecular markers Spi-B (red) and GP2 (green). Spi-B⁺ single-positive cells are immature M cells located near the crypt and have low ability to take up luminal antigens. Spi-B⁺GP2⁺ double-positive cells are functionally mature M cells that are located near the top of the FAE dome of PP and have high uptake capacity. In cecal patches, Spi-B⁺GP2⁺ double-positive cells are rarely detected. See Kimura et al. (8) for details.