Activated human lymphocytes secrete a soluble factor that aggregates leukocytes.

Human polymorphonuclear leukocytes can be activated by various inflammatory stimuli to display increased cell aggregation which is potentially an important pathogenetic mechanism. This study describes a soluble factor produced by concanavalian A-stimulated lymphocytes that causes human leukocytes to aggregate. This factor could be assayed quantitatively by measuring the light absorbance of polynuclear leukocyte suspension using a spectrophotometer. The lymphokine involved, namely the leukocyte aggregating factor (LAgF) was released by non pulse exposure to the mitogen for up to 72 hr with a maximum at 48 hr. LAgF was characterized by Sephadex gel filtration, chromatofocusing, enzymatic and chemical treatment. Sephadex G 100 gel filtration showed LAgF activity in a molecular range of 40,000-65,000. Chromatofocusing of culture supernatant showed LAgF in a single broad peak (4.8-5.4) with a maximum activity at pI 5.2. Human LAgF was heat sensitive, inactivated by treatment with chymotrypsin, and not affected by neuraminidase. Activity was partially recovered from the supernatant after protein precipitation with 1 M perchloric acid and not destroyed by 0.02 M sodium periodate. These findings characterize LAgF as a protein. These data suggest that LAgF is not different from leukocyte inhibiting factor by virtue of its size and physiological properties.