Characterization of B cells within unstructured infiltrates in the inflamed lung
B cells are known to undergo initial activation within secondary lymphoid organs. In the present study, a mouse model based on the adoptive transfer of antigen-specific B and T cells was used to analyze B cell activation and differentiation within unstructured leukocytic infiltrates in the inflamed lung. These infiltrates lacked the characteristics of tertiary lymphoid structures, such as follicular dendritic cells and distinct T and B cell zones. Nevertheless, naïve B cells were activated in the inflamed lung and differentiated into germinal center B cells and plasmablasts. Macrophages were identified as important regulators of this process since they captured antigens in the lungs and presented them to B cells. Coculture experiments using macrophages isolated from the lungs of immunized mice and naïve antigen-specific B cells demonstrated that lung macrophages can activate B cells in vitro. Furthermore, the partial depletion of lung macrophages in vivo resulted in reduced frequencies of antigen-specific B cells in the inflamed lung. This study sheds light on a novel mechanism by which naïve B cells are activated within the inflamed lung in response to antigen.
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