Lymphocyte activation in vivo in the intestinal mucosa of patients with Crohn's disease.

We analyzed lymphocyte activation state in vivo in lamina propria by applying a panel of monoclonal antibodies for cellular activation markers and by identifying different subsets of 3H-thymidine incorporating lymphoblasts by combining autoradiography with immunoperoxidase staining. In focal lymphoblastoid infiltrates 75 +/- 8% of all inflammatory cells displayed Ia, but lymphoid cells expressing 4F2 (40 +/- 6%) and T9 (14 +/- 3%) activation markers were less frequent. The expression of receptors for interleukin-2 (Tac) was particularly low (4 +/- 1%). There were very few 3H-thymidine incorporating cells (labeling index approx. 1%) and most of them belonged to the T cell series. T4+ blasts outnumbered T8+ blasts, and in this numerically minor subpopulation the activated T4/T8 ratio was 2.9 +/- 0.7. Our results suggest that, although a big part of the local inflammatory lymphocytes in Crohn's disease may be activated according to the expression of Ia and 4F2 activation markers, only a fraction of them possess interleukin-2 receptor and have been pushed to the S-phase of the cell cycle.