SARS2 and influenza: Since we had previously localized the BM LLPC compartment into PopD (CD19−CD38hiCD138+)9,16, this population was sorted out of total BM ASC together with PopA (CD19+CD38hiCD138−) and PopB (CD19+CD38hiCD138+), and tested for total IgG secretion as well as SARS2-, influenza-(Flu-), and tetanus toxoid-Tet-) specific IgG secretion by bulk ELISpots.