In Vitro Response of Human Leukocytes to Associated and Dissociated Hemocyanin

Summary Associated (98S) and dissociated (18S) KLH were prepared by rate zonal centrifugation. Peripheral blood leukocytes from unimmunized individuals were cultured with associated or dissociated KLH and the incorporation of 3 H-TdR was determined after 6 days of culture. Associated KLH stimulated 3 H-TdR incorporation 9 to 93 times (mean 38) more than that observed in control cultures without KLH. In contrast the mean incorporation of cultures incubated with dissociated KLH was only 1.3 times that in the controls. Leukocytes obtained from an immunized donor also responded to associated but not to dissociated KLH. We conclude that stimulation of DNA synthesis in human lymphocytes following in vitro exposure to KLH does not require prior in vivo exposure to this antigen, and that this stimulation depends on the molecular size of KLH.