ELISpot and FluoroSpot are some of the most sensitive assays for detecting and quantifying antigen-specific B cells. These methods allow for the assessment of both memory B cells and active antibody-secreting cells, evaluating their antigen-specificity as well as immunoglobulin isotype or subclass. Complement these assays with ELISA to quantify levels of total or antigen-specific immunoglobulin secretion.