B-cell responses against the P1.7-2,4 and P1.5-1,2-2 serosubtypes after OMV immunization on days 0 and 28. (A) Splenic plasma cells, which are defined as IgG-secreting cells from the spleen without the requirement for further ex vivo stimulation. (B) Splenic memory B cells, which are defined as IgG-secreting cells from the spleen after in vitro stimulation. (C) Bone marrow plasma cells, which are defined as IgG-secreting cells from the bone marrow without the requirement for further ex vivo stimulation. Data are from one of two experiments showing similar results.