Antigen-induced proliferative response to murine thymus cells in vitro

Thymus cells from 5- to 6-week-old normal (unimmunized) BALB/c mice showed an increased incorporation of [(3)H]thymidine in the presence of 2,4-dinitrophenyl-bovine serum albumin, fluorescein-bovine serum albumin, and bovine serum albumin (BSA) in tissue culture. The concentrations of antigen (BSA and haptenated proteins) required for stimulation were approximately 25- to 50-fold higher than those of the nonspecific mitogen, concanavalin A. In contrast to the stimulation by concanavalin A, which was maximal at 24 to 72 h, the stimulation by antigen was most marked earlier in the culture period (6 to 24 h). The BSA response was diminished to a statistically significant degree (especially at low BSA concentrations) in thymocytes from animals injected 72 h previously with BSA, indicating that the stimulation is immunologically specific.