Release of soluble interleukin-2 receptors (Tac peptide) in vivo during human immune responses to tuberculin.

Cutaneous levels of soluble interleukin-2 receptor (Tac peptide) have been measured in tuberculin responses in 13 human volunteers by assaying the fluid present in suction-induced blisters at various times after injection of standard purified protein derivative of tuberculin (PPD). Low levels of Tac peptide were found in blisters without prior injection of PPD and in PPD-negative individuals, and maximal levels of Tac peptide were correlated with increased induration at 48 hr (r = 0.69, P = 0.04) in PPD-positive subjects. This is the first report of measurement of Tac peptide in vivo in a defined immune response in man, and may offer a new approach to the study of human immune function in vivo.