In vitro and in vivo responses of B-cell subsets from SAMP8 mice stimulated with LPS ( a ) and ( b ). The indicated B-cell subsets identified as in Figure 1b from spleens of 10-month-old SAMP8 and SAMR1 mice were FACS-purified, and then labeled with the CellTrace Violet kit before culturing for 72 h in the presence or absence of LPS (see Materials and Methods). After culture, the cells were washed and stained to detect CD138 and the incorporated violet dye by flow cytometry. ( a ) Representative results from B1REL, ABC and B2 cells after LPS stimulation are shown. Fluorescence scales are logarithmic. The numbers in the plots are the frequency in each quadrant. Data are means±S.E.M. ( n =3). ( b ) The IgM and IgG1 secreted into the culture medium after 72 h were determined by ELISA. Data are means±S.E.M. ( n =3). Comparisons were made using a two-tailed Student's t -test: * P