Exploring the Role of Microbiota in the Limiting of B1 and MZ B-Cell Numbers by Naturally Secreted Immunoglobulins.

Immunoglobulins (Igs)-or antibodies (Ab)-are important to combat foreign pathogens but also to the immune system homeostasis. We developed the AIDμS mouse model devoid of total soluble Igs and suitable to monitor the role of Igs on immune homeostasis. We used this experimental system to uncover a negative feedback control of marginal zone (MZ) and B1 B cells numbers by naturally secreted Igs. We raised AIDμS mice in germ-free conditions demonstrating that this effect of natural secreted Igs is independent of the microbiota. Herein, we provide a comprehensive description of the protocols to establish and use the AIDμS mice to study the role of total secreted Igs or of different Ig classes. This study involves Igs injections to AIDμS mice or establishment of AIDμS mixed bone marrow chimeras that provide a powerful system to study AIDμS B cells in the presence of stable concentrations of different Ig classes. While we describe flow cytometric and histological methods to analyze MZ and B1 B cell subsets, AIDμS mice can be used to study the effects of natural Igs on other B cell subsets or immune cells.