plasmablast

Plasmablasts are short-lived, antibody-secreting B cells that arise during the early humoral immune response when B cells are activated by antigen and receive help from CD4+ T cells. They originate in extrafollicular foci or as transitional cells within germinal centers and proliferate as they differentiate toward plasma cells, contributing to rapid production of antibodies before more mature plasma cells take over.

Phenotype and markers: Plasmablasts typically express CD19 and reduced levels of CD20, along with high CD38 and often CD27. They upregulate transcription factors such as Blimp-1 (PRDM1) and XBP1, which promote antibody synthesis, and many cells are Ki-67 positive, indicating active proliferation. CD138 may be present but is usually greater on mature plasma cells. They secrete immunoglobulins and can initially favor IgM, with possible class switching depending on environmental signals.

Function and fate: The primary role of plasmablasts is to provide a rapid source of antigen-specific antibodies during early infections or after vaccination. Most plasmablasts are short-lived, dying within a few days, but some can migrate to sites of inflammation or the bone marrow and differentiate into long-lived plasma cells.

Relation to plasma cells: Plasma cells represent a later, terminal differentiation state. They are typically non-proliferative, reside in bone marrow or mucosal tissues, and are characterized by strong CD138 expression and sustained antibody production. Plasmablasts are an intermediate, proliferative stage en route to these mature plasma cells.

Clinical notes: Quantitative increases in circulating plasmablasts can accompany acute infections or vaccinations and may correlate with antibody response magnitude. Abnormal plasmablast expansion can be observed in certain autoimmune diseases and plasma cell disorders.