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Antigen-specific B cells bifurcate into antibody secreting cells (ASC) and memory B cells after infection or vaccination. ASCs or plasmablasts have been extensively studied in humans but less is known about B cells that get activated but do not differentiate into early plasmablasts. Here, we define the phenotype and transcriptional program of an antigen-specific B cell subset, referred to as activated B cells (ABC), that is distinct from ASCs and is committed to the memory B cell lineage. ABCs were detected in humans after infection with Ebola virus or influenza virus and also after vaccination. By simultaneously analyzing antigen-specific ASCs and ABCs in human blood after influenza vaccination we interrogated the clonal overlap and extent of somatic hypermutation (SHM) in the ASC (effector) and ABC (memory) lineages. Longitudinal tracking of vaccination-induced HA-specific clones revealed minimal increase in SHM over time suggesting that repeated annual immunization may have limitations in enhancing the quality of influenza-specific antibody.

Four Ebola patients received care at Emory University Hospital, presenting a unique opportunity to examine the cellular immune responses during acute Ebola virus infection. We found striking activation of both B and T cells in all four patients. Plasmablast frequencies were 10-50% of B cells, compared with less than 1% in healthy individuals. Many of these proliferating plasmablasts were IgG-positive, and this finding coincided with the presence of Ebola virus-specific IgG in the serum. Activated CD4 T cells ranged from 5 to 30%, compared with 1-2% in healthy controls. The most pronounced responses were seen in CD8 T cells, with over 50% of the CD8 T cells expressing markers of activation and proliferation. Taken together, these results suggest that all four patients developed robust immune responses during the acute phase of Ebola virus infection, a finding that would not have been predicted based on our current assumptions about the highly immunosuppressive nature of Ebola virus. Also, quite surprisingly, we found sustained immune activation after the virus was cleared from the plasma, observed most strikingly in the persistence of activated CD8 T cells, even 1 mo after the patients' discharge from the hospital. These results suggest continued antigen stimulation after resolution of the disease. From these convalescent time points, we identified CD4 and CD8 T-cell responses to several Ebola virus proteins, most notably the viral nucleoprotein. Knowledge of the viral proteins targeted by T cells during natural infection should be useful in designing vaccines against Ebola virus.Ebola infection | human immune response | immune activation | plasmablasts | T cells

Ebolaviruses are pathogenic agents associated with a severe, potentially fatal, systemic disease in man and great apes. Four species of ebolaviruses have been identified in west or equatorial Africa. Once the more virulent forms enter the human population, transmission occurs primarily through contact with infected body fluids and can result in major epidemics in under-resourced settings. These viruses cause a disease characterised by systemic viral replication, immune suppression, abnormal inflammatory responses, major fluid and electrolyte losses, and high mortality. Despite recent progress on vaccines, and with no licensed prophylaxis or treatment available, case management is essentially supportive with management of severe multiple organ failure resulting from immune-mediated cell damage. The 2013-16 outbreak was classified by WHO as a Public Health Emergency of International Concern, which drew attention to the challenges of diseases caused by infections with ebolaviruses and questioned scientific, clinical, and societal preparation to handle future epidemics.

West Africa is currently experiencing the largest outbreak of Ebola virus disease (EVD) in history. Two patients with EVD were transferred from Liberia to our hospital in the United States for ongoing care. Malaria had also been diagnosed in one patient, who was treated for it early in the course of EVD. The two patients had substantial intravascular volume depletion and marked electrolyte abnormalities. We undertook aggressive supportive measures of hydration (typically, 3 to 5 liters of intravenous fluids per day early in the course of care) and electrolyte correction. As the patients' condition improved clinically, there was a concomitant decline in the amount of virus detected in plasma.