Further studies on the role of circulating lymphocytes in the initiation of primary antibody responses to different antigens.

Thoracic duct cells obtained from normal (unimmunized) donors restored the primary hemolysin response of lethally irradiated or neonatally thymectomized rats to sheep red blood cells. Synergy between thoracic duct cells and bone-marrow cells was demonstrated in the irradiated hosts. However, thoracic duct cells did not restore the primary antibody response of irradiated rats challenged with diphtheria toxoid, but did restore the response of neonatally thymectomized rats. The addition of peritoneal exudate cells or bone-marrow cells to inocula of thoracic duct cells also failed to restore the response of irradiated hosts to diphtheria toxoid, although normal spleen cells restored the response. These findings indicate that the cellular events involved in the initiation of the primary antibody response to sheep red blood cells differ from those involved in the response to diphtheria toxoid.