Physicochemical properties of T-cell-activating monokines in guinea pigs.

T-cell-activating monokines of guinea pigs with interleukin 1-like activity were produced in protein-free medium by stimulation of peritoneal macrophages with synthetic muramyl dipeptide (MDP). Gel filtration of the culture supernatant of MDP-stimulated macrophages revealed that most of the activity to potentiate the responses of thymocytes and lymph node T cells to phytohemagglutinin were found in the high-molecular-weight (40,000-80,000) fraction. By isoelectric focusing, the monokine in the high-molecular-weight fraction was focused at a pI of around 4.7 forming a somewhat broad band, indicating some heterogeneity. In the analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the high-molecular-weight fraction, the peak of the activity was found at an approximate Mr of 60K under unreduced as well as reduced conditions. Accordingly, it is likely that the monokine in this fraction is a polypeptide of 60K, but a possibility still remains that the 60K component is an aggregate of low-molecular-weight monokine which requires more rigorous conditions for dissociation.