Sample collection: Seven to sixty days post-immunization, mice were anesthetized with isoflurane and blood was collected from the orbital sinus using capillary tubes without anticoagulant for sera separation. Inguinal and popliteal lymph nodes (LNs), spleens and both tibias and femurs were harvested and placed in cold complete Dulbecco’s Modified Eagle’s Medium [(DMEM, Corning, T10014CV) containing 10% heat inactivated Fetal Bovine Serum (FBS, Corning, 35-015), 1% Glutamax (Gibco, 35050-061) and 1% Penicillin/Streptomycin (Gibco, 5070063)]. All organs were kept on ice and immediately processed after collection.
LNs and spleen processing: Organs were homogenized with a syringe plunger and filtered through a 40 μm cell strainer on ice. Red blood cells (RBCs) of spleens were lysed using ACK lysing buffer (Lonza, 10-548E) for 5-8 minutes on ice and the reaction was stopped with cold PBS.
Bone Marrow (BM) processing: BM was flushed from both femurs and tibias from each mouse using a 1 mL 25 G x 5/8” syringe (BD Biosciences, 30962). RBCs were lysed as described above.
Cells from all tissues were resuspended in ice cold complete DMEM and immediately used for counting, culture, or staining.
Serum processing. Following collection, blood was centrifuged at 14,000 x g (maximum speed) for 30 minutes, 4°C. Serum was recovered and stored at -20°C for neutralization assays and ELISAs.