Soluble chemotactic factors are released upon Fas engagement. Indirect granulocyte recruitment and efficiency of the neutralizing FasL antibody in cell-based assays (□). Granulocyte migration induced by CD56⁺CD3⁺ supernatants (▪); cells were treated with FasL, supernatants were cleared on a 100-kDa filter and concentrated 5-fold on a 1-kDa filter. Supernatant dilutions were used in migration assays alone or with the neutralizing NOK-1 FasL antibody. The horizontal line at migration index 1.0 indicates lack of chemotaxis. The presence of labile factors in the supernatant was confirmed by heat-inactivation of 30 minutes at 95°C. Data shown are the mean ± SEM of 2 independent experiments.