THYMIC FUNCTION IN NZB MICE .5. DECREASED NK ACTIVITY IN NZB MICE TREATED WITH A CIRCULATING THYMIC-FACTOR

NZB mice spontaneously showing high natural killer (NK) activity and lacking a serum thymic factor (FTS) were treated with synthetic FTS itself or with a structural analog of FTS chosen for its prolonged half life in the serum and used at a lower dose. Both treatments resulted in decreased NK activity in NZB mice of both sexes. Spleen cells from FTS-treated NZB mice, when added to spleen cells from control NZB mice, inhibited their NK activity, suggesting the activation of suppressor cells of NK activity by FTS treatment.