B-memory response after tumor necrosis factor kinoid (TNF-K) immunization. Thirty-six human tumor necrosis factor-alpha (hTNF-α) transgenic mice were immunized with TNF-K at 7 (day 0), 8 (day 7), and 11 (day 28) weeks of age. Bleeding was done every month from 12 weeks of age (day 38) until sacrifice. When we observed a decline of the anti-hTNF-α neutralizing antibody titer (closed symbols), we injected intraperitoneally (arrow) native hTNF-α (10 ng, n = 10, diamonds) (a, b), native hTNF-α (100 ng, n = 9, squares) (c, d), keyhole limpet hemocyanin (KLH) (10 μg, n = 10, circles) (e, f), or phosphate-buffered saline (equivalent volume, n = 10, triangles) (g, h). We studied the anti-KLH antibody titer (open symbols) and neutralizing anti-hTNF-α antibody titer (closed symbols) for 10 weeks (70 days). Each single plot represents the antibody titer of one mouse. The bold line represents the mean antibody titer at each time point. *P < 0.001 versus day 149; **P < 0.0001 versus day 171; #P < 0.05 versus day 178; ##P < 0.05 versus day 149. NC50, mean of the reciprocal of the serum dilution that neutralizes 50% of hTNF-α activity.