Although IL-8 has been reported to be a chemoattractant for T cells in vivo and in vitro, this has been a controversial issue. By using freshly purified human T cells (>90% CD3(+)), we demonstrated consistent T-cell migration in response to recombinant human IL-8 in vitro. However, highly purified T cells, when incubated at 37°C for more than 12 h or cultured overnight in the presence of anti-CD3 antibody, showed a markedly reduced capacity to migrate in response to IL-8. This reduction in chemotaxis was associated with a decrease in binding of 125I-IL-8 to T cells. Northern blots showed that freshly purified T cells expressed both IL-8 receptor type A and type B transcripts. Steady-state levels of mRNA for IL-8RA and IL-8RB in T cells were progressively reduced with time by incubation of the cells at 37°C with or without anti-CD3. The inability of cultured T cells to migrate in response to IL-8 accounts for the contradictory published reports on this issue. In vivo administration of IL-8 in rats resulted in the infiltration at the injection site of neutrophils followed by T cells, and this later T-cell infiltration was reported to be partially blocked by selective depletion of neutrophils. These observations raised the possibility that IL-8 may trigger neutrophils to release a factor(s) that may also participate in the T-cell recruitment. Neutrophil granule proteins, defensins, and CAP37/azurocidin released upon stimulation of cells by IL-8 were shown to induce human T-cell migration in vitro. Subcutaneous injection of defensins into SCID mice engrafted with human PBL resulted in significant infiltration by human CD3(+) T lymphocytes. These results indicate that IL-8 is able not only to act directly and induce migration of T lymphocytes that express IL-8 receptors, but also to act indirectly by activating neutrophils to release additional T-cell chemoattractants.