TNF expression in memory, naive, and GC B lymphocytes. (A) RT-PCR analysis of TNF gene expression in purified memory, naive, and GC B-cell fractions. The size of the expected fragments is indicated on the right. (B) TNF production by purified memory, naive, and GC B lymphocytes after 48-hours culture in the absence (▪) or presence (□) of PMA and A23187. TNF in culture supernatants was assayed by ELISA. Results are means ± SE from three experiments and are expressed as pg/mL.