Background: Perforin is known to be important in cytolytic activity mediated by natural killer (NK) cells.  
Objective: To study the relationship between the efficiency of NK and lymphokine-activated killer (LAK) cells activity, and the expression of perforin and HLA class I molecules.  
Methods: LAK cells were generated by in vitro culturing of human peripheral blood lymphocytes (PBLs) in the presence of human recombinant interleukin-2 (rIL-2). Cytotoxic activity was measured at different intervals of activation by MTT colorimetric assay using different human tumor cell lines. Immunocytochemical staining of molecules was performed on LAK/NK cells using specific monoclonal antibodies and Biotin-conjugated anti-immunoglobulin.
Results: LAK/NK killing against Fen and two other cell lines, KB and Scaber showed that at day 9 and 15 of activation, 57% to 60% and 45.5% to 92.5% of Fen cells were killed at different E/T ratios. At the same time, the maximum percent killing against Scaber and KB cell lines was 47.3 and 54.3 at 5/1 ratio, respectively, showing that Fen cells were more sensitive than the two other cells. Time-course experiments using Fen cell line demonstrated 60.0, 83.9 and 34.8 percent killing at days 9, 15 and 22 at 10/1 E/T ratios. When other E/T ratios were investigated, a similar profile was observed. The maximum activity was at day 15 and 5/1 E/T ratio (92.5%). In immunocytochemical staining of activated LAK cells, 75.9% to 86.3% of LAK cells expressed HLA class I molecules. Perforin expression changed from 30.3% at day 7 to 42.7% at day 17 followed by a decrease to 27.9% at day 24.  
Conclusion: These data indicate that perforin expression is closely correlated with NK/LAK killing activity.