Abstracts of Papers Presented at the Third International Complement Workshop, Harvard Medical School, Boston, Massachusetts, June 3–5, 1968

Abstract Human eosinophils obtained by dextran sedimentation of human blood containing a leukocyte differential with greater than 75% eosinophils have been studied for chemotaxis using the modified Boyden chamber. Eosinophils respond to fresh homologous serum treated with immune complexes or plasmin. Ultracentrifugal analysis in sucrose density gradients reveals that neutrophils and eosinophils respond chemotactically to identical fractions from the gradients. In serum treated with immune complexes, the zone of chemotactic activity sediments with a moderately rapid velocity corresponding to the position of C′(5,6,7)a; whereas in the plasmin-treated serum, activity is confined to the upper portion of the gradient, probably representing the C′3 fragment. Like neutrophils, eosinophils also respond to soluble bacterial factors. Thus, eosinophils and neutrophils appear to respond to identical chemotactic factors. When human C′5 (β1F globulin) prepared according to the method of Nilsson and Müller-Eberhard is treated with trypsin, chemotactic activity for neutrophils appears. The intensity of the activity is a function of the duration of treatment with trypsin. Sucrose density gradient analysis reveals a chemotactic factor in the trypsin-treated C′5 preparation that sediments very slowly. In Sephadex G 75 the chemotactic activity elutes in a zone between cytochrome c and glucagon markers. The molecular weight of the chemotactically active C′5 fragment appears to be approximately 8500. The relation of this fragment to the C′5 anaphylatoxin fragment is not known. With appropriate concentrations of C′5, it is also possible to generate chemotactic activity by addition of C′5 to EAC′1,4, 2,3 cells. This activity sediments very slowly in the ultracentrifuge. C′3 treated with trypsin liberates a chemotactically active fragment, but in this regard C′3 appears to be less active than C′5.