Figure 3.

Architectural changes in the splenic microenvironment following immunization with a T‐independent antigen. (a) Blood was taken from young (1 month) and old (18 months) mice at days 0, 3, 7, 14, 21 and 28 after immunization with trintriphenyl (TNP) –Ficoll and the specific anti‐IgM TNP–Ficoll response was determined by ELISA. Both young and old mice show a similar increase in the IgM response after immunization, although the level of the anti‐IgM TNP–Ficoll antibody is initially higher at days 0 and 3 in older animals. Six mice were used for each time‐point. *P < 0·05; ***P < 0·001. Data representative of three experiments. (b) Splenic sections of young and old mice were stained to detect T (red) and B (green) cells and marginal zone macrophages (MZM; red) and marginal metallophilic macrophages (MMM; green). Following immunization, the distinct demarcation of the T‐ and B‐cell zone of both age groups is disrupted (day 3), which is resolved by day 28 in young mice, but is still disorganized in the spleen of old mice. Magnification ×100. Insert of an area highlighted by a white box is shown representing a higher magnification (×200). In the spleen of young mice MMM and MZM encircle the marginal zone, which is incomplete, despite the appearance of MZM, in old animals. Magnification ×100. Isotype controls revealed no staining (data not shown). Data representative of four experiments.