B cells modulate mucosal associated invariant T cell immune responses

Area of Science:

• Immunology
• Microbiology
• Vaccinology

Background:

• Pre-existing T cell immunity to enteric bacterial vaccines is common but poorly understood.
• Mucosal associated invariant T (MAIT) cells exhibit broad immune responses to various microbes, including enteric bacteria.

Purpose of the Study:

• To investigate if MAIT cell responses to intestinal bacteria contribute to pre-existing immunity observed before enteric vaccine administration.
• To explore the role of B cells in presenting antigens to MAIT cells in the context of gut microbiota surveillance.

Main Methods:

• Measurement of MAIT cell immune responses in healthy individuals without prior oral immunization.
• Assessment of MAIT cell activation by B cells infected with commensal and pathogenic enteric bacteria (Enterobacteriaceae family).
• Analysis of MR1 restriction, endocytic pathway involvement, and cytokine profiles in response to varying bacterial loads.

Main Results:

• MAIT cells were activated by B cells infected with diverse enteric bacteria but not by uninfected cells.
• MAIT cell activation was MR1-restricted and involved the endocytic pathway.
• Cytokine profiles of MAIT cell responses depended on bacterial load, suggesting a threshold for MR1 expression is necessary for activation.

Conclusions:

• B cells act as antigen-presenting cells for MAIT cells in response to enteric bacterial infections.
• MAIT cell responses are influenced by bacterial load and MR1 expression thresholds.
• These findings offer insights into gut immune surveillance and the nature of background immune responses to enteric bacteria.