Generation of migratory antigen-specific plasma blasts and mobilization of resident plasma cells in a secondary immune response

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Abstract
Maintenance of protective humoral immunity depends on the generation and survival of antibody-secreting cells. The bone marrow provides niches for long-term survival of plasma cells generated in the course of systemic immune responses in secondary lymphoid organs. Here, we have analyzed migratory human plasma blasts and plasma cells after secondary vaccination with tetanus toxin. On days 6 and 7 after immunization, CD19+/CD27high/intracellular immunoglobulin Ghigh (IgGhigh)/HLA-DRhigh/CD38high/CD20–/CD95+ tetanus toxin–specific antibody-secreting plasma blasts were released in large numbers from the secondary lymphoid organs into the blood. These cells show chemotactic responsiveness toward ligands for CXCR3 and CXCR4, probably guiding them to the bone marrow or inflamed tissue. At the same time, a population of CD19+/CD27high/intracellular IgGhigh/HLA-DRlow/CD38+/CD20–/CD95+ cells appeared in the blood in large numbers. These cells, with the phenotype of long-lived plasma cells, secreted antibodies of unknown specificity, not tetanus toxoid. The appearance of these plasma cells in the blood indicates successful competition for survival niches in the bone marrow between newly generated plasma blasts and resident plasma cells as a fundamental mechanism for the establishment of humoral memory and its plasticity.