Serum factors modulating in vitro migration of thymus lymphocytes

Migration of guinea pig thymocytes in sealed glass capillaries was measured in 3 intervals during 24 h of incubation. Two factors present in guinea pig sera which stimulated migration were partly characterized. One factor, with a molecular weight between 10,000 and 100,000 (as judged by ultrafiltration), stimulated migration during the first 2 h of incubation but not later. Only about one third of the sera had this activity. The other factor, which was present in most sera, had a molecular weight exceeding 100,000 and stimulated migration only at later times. Both factors were heat stable and resisted freezing and thawing as well as lyophilization, but were inactivated by storage of sera. Normal human sera stimulated migration from 2 h after start of incubation but, in contrast to guinea pig sera, had a slightly inhibitory effect during the first 2 h. Thymectomy had no effect on guinea pig or human sera as regards ability to modulate migration. Patients with defects in cell mediated immunity did not exhibit any specific alterations in serum activity. However, active disease as well as operations performed on guinea pigs reduced the late stimulatory activity. Additional experiments indicated that migration of thymus cells in glass capillaries depends partly on factors other than cell motility.