Table 2.

Comparative immunological effects in the absence of natural antigen stimulation (diet protein versus microbiota).

Models	Protein-free diet mice	Germ-free mice
Small intestine (villi)	Lost the typical pleated appearance (Menezes et al., 2003)	Thin and more pointed at the tip (Thompson and Trexler, 1971)
Large intestine	No differences (Menezes et al., 2003)	Megacaecum (Thompson and Trexler, 1971)
Peyer patches (PP)	Smaller (Menezes et al., 2003)	Smaller (Thompson and Trexler, 1971)
Lamina propria (LP)	↓Number of lamina propria cells (Menezes et al., 2003)	↓Number of lamina propria cells (Thompson and Trexler, 1971)
Intraepithelial lymphocytes (IEL)	↓Number	↓Number
	↓%TCR αβ	Cytotoxicity compromised (Umesaki et al., 1993; Imaoka et al., 1996)
	↑%TCR γδ (Menezes et al., 2003)
Immunoglobulins	↓sIgA	↓sIgA
	↓Ig, IgG, and IgA (Menezes et al., 2003)	↓Ig, IgG, and IgA (Nielsen and Friis, 1980)
Infection susceptibility	↑Susceptible to Leishmania major (Amaral et al., 2010)	↑Susceptible to Leishmania major and others (Oliveira et al., 2005)

↑, increased; ↓, depressed; secretory IgA (sIgA).