Stimulation by autologous serum preheated at 66 °C of the incorporation of [3H]uridine by cultured lymphocytes: comparison with stimulation by concanavalin A

Rabbit serum, preheated at 66 °C for 30 min, produced a stimulation of the incorporation of [3H]uridine by cultured autologous lymph-node cells similar to that caused by concanavalin A (Con-A). However, whereas the percentage stimulation by Con-A increased with time, that by serum preheated at 66 °C (66 °C-serum) reached a peak after 3–4 h and then declined. The decline was greater at higher cell concentrations. Isotope-dilution studies showed that stimulation at 3 h by 66 °C-serum or by Con-A reflected an increase in the maximum velocity of the rate-limiting step for incorporation of [3H]uridine and not a decrease in the pool of uridine and (or) uridine competitors. Experiments in which serum concentration and the relative proportions of serum preheated at 66 °C and serum preheated at 37 °C were varied, suggested that preheating serum at 66 °C removes an inhibitory factor and exposes a stimulatory factor. The stimulatory activity of 66 °C-serum was not dialysable. The results are compatible with a model ...