Supernatants of stored polymorphonuclear neutrophils exhibit growth-promoting activity in several cell lines: perforin expression in polymorphonuclear neutrophils and its role in down-regulation of growth-promoting activity.

OBJECTIVE

Polymorphonuclear neutrophils (PMNs) play important roles in the host immune defence. This study was performed to identify roles of PMNs other than those already known.

METHODS

PMNs were separated from the peripheral blood of healthy individuals and stored in vitro for 24 h in the presence or absence of an anti-human Fc receptor (FcR) gamma III antibody, namely, anti-CD16 monoclonal antibody (mAb). Stored supernatants were harvested and incubated with several leukaemia and transformed cell lines for 48 h. The increase in growth rate was assessed by the increase in the amount of 3H-thymidine incorporated into these cells. Expression of perforin on PMNs, which is thought to decrease cell viability, was elucidated by flow cytometry (FCM) analysis. The presence of perforin in the stored supernatants was determined using an enzyme-linked immunosorbent assay (ELISA). A serine protease inhibitor, which is known to block the effect of perforin, was added to the cultures of several leukaemia and transformed cell lines to confirm the effect of perforin in reducing cell viability.

RESULTS

Growth promotion of some cell lines cultured with the stored supernatants of PMNs was observed both in the presence and absence of anti-CD16 mAb, which was used as a trigger molecule of PMNs. This was particularly notable in the case of Raji and Daudi (both Burkitt lymphoma) cell lines and Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cell lines (B-LCLs) derived from healthy individuals. Perforin expression was observed in both freshly prepared and stored PMNs, regardless of the presence or absence of anti-CD16 mAb. ELISA also detected perforin in the stored supernatants in both the presence and absence of anti-CD16 mAb. The increase in growth rate was induced in the presence of not only a serine protease inhibitor but also an anti-perforin mAb.

CONCLUSIONS

Stored supernatants of PMNs exhibit up-regulation of cell growth in several cell lines; this up-regulation is particularly prominent in B-lineage cell lines. Furthermore, perforin appeared to be expressed on PMNs constitutively and secreted into the extracellular fluid. Results of this study strongly suggest that the growth-promoting activity in supernatants of stored PMNs is partially inhibited by perforin, which is thought to be produced by PMNs themselves.