Thymic stromal cells change in number and proportion throughout development. (A) Graph of the total thymic cellularity at various ages. (B) CD45^– thymic stromal cell number per thymus (solid line) and the proportion of thymic cellularity they compose (dashed line) at different ages. (C) Thymocyte-to-CD45^– thymic stromal cell ratios at various time points. Means and standard errors from 2 to 5 experiments derived from digests of at least 3 thymi pooled for each time point are shown for all graphs.