Abstract
Culture medium from bovine peripheral blood mononuclear cells stimulated with the mitogens phytohaemagglutinin (PHA) or Concanavalin A (Con A) was found to maintain the proliferation of Con A blasts in vitro. The factor responsible for this activity was not absorbable with bovine erythrocytes or fresh peripheral blood lymphocytes but was removed by Con A blasts. Production of this factor was dependent on the dose of mitogen used and was greatest after 24 h culture compared to 48 h. Quantitative determinations of factor activity in supernatants were carried out by regression analysis of logit transformed data from assays measuring the maintenance of Con A blast proliferation by supernatants.