Lung B cells in ectopic germinal centres undergo affinity maturation

Chronic exposure to allergens and other airborne antigens can result in the formation of lymphocyte aggregates in the lung, which can harbour ectopic germinal centres (GCs). After allergen exposure, GCs that form in the lung are much smaller and less densely packed with B cells than lymph node GCs. Despite this, ectopic lung GCs can support somatic hypermutation and affinity-based maturation as in lymph node GCs, and can export memory B cells directly into the lung tissue. This demonstrates that the lung itself can locally diversify B cell responses and support the generation of tissue memory B cell populations in situ. Here, we have employed a single cell sequencing approach using 10x Genomics scRNAseq and BCRseq to study germinal centre B cell clonal sharing between the mediastinal lymph node and lungs of mice. Overall design: C57BL/6 mice were adoptively transfered 50,000 B1-8i cells, followed by four intranasal doses of 4-Hydroxy-3-nitrophenylacetyl (NP) hapten conjugated to keyhole limpet hemocyanin (KLH) in tandem with house dust mite (HDM); NP-KLH/HDM. 21 days post-transfer, the lungs and mediastinal lymph node were collected and and processed to generate single-cell suspensions for fluorescence-activated cell sorting (FACS). Endogenous germinal centre B cells and memory B cells were isolated by FACS for analysis using scRNA-seq and scBCR-seq.