library_construction_protocol: For single cell RNA sequencing, single cell suspensions were prepared from draining lymph nodes of immunized mice and treated mice. Single cell suspensions were indexed with TotalSeqC (BioLegend) cell surface antibodies. Gross or fractionated GC cells were purified by flow cytometry, pooled and loaded onto a Chromium Controller (10x Genomics). Single-cell RNA-seq libraries were prepared using the Chromium Single Cell 5′ v2 Reagent Kit (10x Genomics) according to manufacturer's protocol. Libraries were loaded onto an Illumina NextSeq with the mid-Output Kit (150 paired end) for V-D-J analysis or onto an NOVAseq for pooled V-D-J and single  cell gene expression. Hashtag indexing was used to demultiplex the sequencing data and generate gene-barcode matrices, respectively.