**3. The intestinal immune system**

The intestinal immune system is the most extensive lymphoid tissue, given the enormous surface area of the intestinal mucosa with which it is associated. It is called gut-associated lymphoid tissue (GALT) and is mainly composed of: organized lymphatic follicles, called Peyer's patches (PPs); mesenteric lymph nodes (MLN); *lamina propria* lymphocytes (LPLs); intraepithelial lymphocytes (IELs) (**Figure 2**) [1].
