Microbiota modulate immune cell populations and drive dynamic structural changes in gut-associated lymphoid tissue

Area of Science:

• Immunology
• Microbiology
• Gastroenterology

Background:

• Inbred mice offer homogeneity but exhibit variability due to environmental and developmental factors, impacting experimental reproducibility.
• Gut-associated lymphoid tissue (GALT) development and function are influenced by the gut microbiota.
• Understanding microbiota-induced changes in GALT is crucial for improving mouse models in research.

Purpose of the Study:

• To investigate the impact of microbiota on the development and cellular composition of gut-associated lymphoid tissue (GALT) in mice.
• To quantify differences in antigen-presenting cells (APCs) and lymphoid structures across germ-free, conventionally colonized, and minimally colonized mouse models.
• To assess the role of a defined minimal microbiota (oMM12) in standardizing GALT development for enhanced experimental reproducibility.

Main Methods:

• Microscopic and cytometric techniques were employed to analyze GALT in MHC II-EGFP knock-in mice.
• Comparison of germ-free (GF), conventional (CV), and oMM12-colonized mice.
• Quantification of antigen-presenting cells (APCs) in various GALT compartments including lamina propria, cryptopatches (CP), isolated lymphoid follicles (ILFs), Peyer's patches (PPs), and mesenteric lymphoid complex.

Main Results:

• Germ-free mice exhibited larger intestinal surface area but lower villi density and fewer APCs in the lamina propria compared to conventionally colonized and oMM12-colonized mice.
• Solitary intestinal lymphoid tissue (SILT) volume was significantly smaller in GF mice.
• Peyer's patches (PPs) and cecal patches showed distinct morphological and cellular differences between GF, oMM12, and CV mice, with GF mice having smaller PP follicles and fewer pDCs in PPs.

Conclusions:

• Microbiota plays a critical role in regulating the differentiation of SILT, the size and morphology of PPs, mesenteric lymph nodes (MLNs) cellularity, and cecal patch morphology.
• Microbiota directly influences the functional configuration of the immune system and the differentiation of lymphoid structures.
• Standardized microbiota, like oMM12, can significantly improve reproducibility in animal studies by enabling microbiologically controlled experiments.