Differential regulation of T- and B-lymphocyte activation in severely burned patients.

We studied the in vitro expression and regulation of the CD23 and CD25 (Tac) surface antigens by peripheral blood lymphocytes (PBL) from severely burned patients (burn injuries ranging from 25% to 72% TBSA) in order to evaluate T- and B-lymphocyte activation processes after thermal trauma. The spontaneous and cytokine (IL-4, IL-2)-induced expression of CD23 which represents a B-cell activation marker was significantly reduced during the second to fifth week postburn when compared to healthy donors. In contrast, CD25, which is expressed on activated T cells, showed a marked increase both spontaneously, indicating an in vivo activation, and after stimulation with IL-2 or PHA. Concomitantly, T-cell proliferation induced by PHA or Con A was suppressed. However, the number of T and B cells remained unchanged. The data demonstrate the impairment of early events in the lymphocyte program in severely burned patients. The activation of B cells is downregulated, since they become refractory to external helper signals. In addition, T cells are highly activated but fail to proceed to proliferation in response to mitogenic stimuli.