Comparison and Yield of Antigen- or Mitogen-Induced Human Lymphotoxins

Abstract

The yield of lymphotoxin (LT) in cultures of human lymphocytes stimulated with a mitogen, phytohemagglutinin (PHA), is about 60 times greater than that obtained by antigenic stimulation with mixed lymphocyte cultures. Lymphotoxin induced under both conditions behaved identically when we employed electrophoresis on 9% acrylamide gel (pH 8.6 or 7.4), ultracentrifugation in 3 to 10% sucrose density gradients, and testing for pH stability. Both LT were neutralized in like degree by the addition of anti-LT serum against purified PHA-induced human LT. Thus, utilizing multiple analytical methods based on diverse principles, we found no differences in the two LT, strongly implying that both types are indeed identical. The two major implications of this conclusion are: 1) Although under natural in vivo conditions, only antigen-induced LT would be operative, in the light of our findings, mitogen-induced LT may also be used in biologically meaningful experiments. 2) Furthermore, the larger yield of mitogen-induced LT represents a great advantage in purification of the lymphocyte mediator present in the starting material only in small amounts. In addition, it is of interest that 89% of the cytotoxic activity of crude LT induced by PHA stimulation can be neutralized by antiserum prepared against purified LT, an indication that the bulk of the cytotoxicity in crude LT appears to be due to the cytotoxin comprising our purified LT preparation.