Antigen flow is restricted in immunized mice upon re-exposure to that antigen. (A, B) Mice were immunized twice with intraperitoneal injections of KLH and alum or saline and alum. Two weeks after the second injection, 200 µg of KLH-800CW was injected subcutaneously into the dorsum of the hind paw. (A) A lesser antigen signal was observed in the sciatic lymph nodes of KLH-immunized mice as compared with naïve mice. Images are representative; triangles indicate popliteal lymph nodes and stars represent sciatic lymph nodes. (B) Data shown are individual values (naïve, 54.34 ± 8.840, n = 5 versus KLH-immunized, 9.730 ± 3.715, n = 5, p < .001 by t test). (C) This effect was specific to the immunized antigen, as OVA signal injected in a mouse immunized to KLH was not reduced, but OVA injected into OVA-immunized mice was reduced. Images are representative of five animals per group. (D) Antigen signal in the sciatic lymph node remained less in mice injected in the foot for at least 17 wks after booster injection. Antigen signal from the sciatic lymph node in animals immunized with KLH-800CW was determined at various time points following booster injection with KLH. The hashed line at the top of the figure represents the mean antigen signal detected in sciatic lymph nodes of saline-immunized control animals, as displayed in Figure 2B. Data represent mean ± SEM. Dotted line indicates average naïve mouse antigen signal. n = 5 to 8.