Model for T-cell differentiation in healthy controls and patients with RA.

The models are based on flow cytometry data (Figure 1) and TREC content of individual subsets (Figure 4). Each subset is represented by a box. White boxes represent subsets found in healthy controls, and gray boxes represent subsets found predominantly in RA patients. Subsets are characterized as TREC rich, TREC high, TREC intermediate (int), and TREC poor, in relation to other subsets from the same pathway (ie, health or RA). In healthy controls we have proposed 2 pathways, culminating in conventional and central memory T cells. In RA, there is proliferation, differentiation, or both within the naive subset, indicated by a circular arrow, resulting in the appearance of atypical subsets that are TREC high. The conventional memory pathway can still be identified, but the central memory pathway cannot. Atypical CD45RB^dull CD45RA⁻ CD45RO⁻CD62L⁺ cells are also present.