Human anti-smallpox long-lived memory B cells are defined by dynamic interactions in the splenic niche and long-lasting germinal center imprinting

Memory B cells (MBCs) can persist for a lifetime, but the mechanisms that allow their long-term survival remain poorly understood. Here, we isolated and analyzed human splenic smallpox/vaccinia protein B5-specific MBCs in individuals who were vaccinated more than 40 years ago. Only a handful of clones persisted over such an extended period, and they displayed limited intra-clonal diversity with signs of extensive affinity-based selection. These long-lived MBCs appeared enriched in a CD21hiCD20hi IgG+ splenic B cell subset displaying a marginal-zone-like NOTCH/MYC-driven signature, but they did not harbor a unique longevity-associated transcriptional or metabolic profile. Finally, the telomeres of B5-specific, long-lived MBCs were longer than those in patient-paired naive B cells in all the samples analyzed. Overall, these results imply that separate mechanisms such as early telomere elongation, affinity selection during the contraction phase, and access to a specific niche contribute to ensuring the functional longevity of MBCs.

BLI-MS: Combining biolayer interferometry and mass spectrometry

Biolayer Interferometry (BLI) is a technology which allows to study the affinity between two interacting macro-molecules and to visualize their kinetic of interaction in real time. In this work we combine BLI interaction measurement with mass spectrometry in order to identify the proteins interacting with the bait. We provide for the first time the proof of concept of the feasibility of BLI-MS in complex biological mixtures. Data are available via ProteomeXchange with the identifier PXD019440. This article is protected by copyright. All rights reserved.

HLA molecule expression on the surface of cells and microparticles in platelet concentrates

BACKGROUND

Platelet (PLT) transfusions are an essential treatment for bleeding disorders. However, immunologic complications can occur, including alloantibody production against Class I HLA molecules. The principal source of HLA molecules in PLT concentrates (PCs) is the PLTs themselves. However, extracellular microparticles (MPs) present in PCs may express HLA molecules.

STUDY DESIGN AND METHODS

We used nanoscale flow cytometry to explore the expression of HLA-A2, HLA-B7, and HLA-B57 on the surface of cells, PLT-derived MPs (PMPs), lymphocyte-derived MPs (LMPs), and monocyte-derived MPs (MMPs) present in PCs. Expression was studied during 7 days of storage.

RESULTS

Platelets were not the only source of HLA molecules in PCs. HLA molecules were present on PMPs, LMPs, and MMPs. The level of HLA Class I molecule expression varied between haplotypes and MPs of different origins and during storage.

CONCLUSION

Platelets or residual cells remaining after leukoreduction are not the only source of HLA Class I molecules in PCs, highlighting the contribution of MPs to alloimmunization mechanisms. These data may be relevant for the development of new transfusion guidelines.