Soluble HLA class I molecules in malignant pleural and peritoneal effusions and its possible role on NK and LAK cytotoxicity

Purpose: To examine the amount of sHLA-I in malignant pleural and peritoneal effusions and its possible role in natural immune defense. Methods: Three groups of patients (75 patients with malignancy, 21 with infection, and 27 with other diseases) were studied for sHLA-I value using an ELISA method. Cytolytic activity of freshly isolated pleural and peritoneal effusion-associated lymphoid (EAL) cells from 14 of cases with malignancy were examined and compared to that of ten non-cancerous patients. EAL cells were co-cultured with the autologous cell-free effusions immediately after collection and 3 days after incubation with IL-2. Results: The mean value of sHLA-I in effusions was 1.01 +/- 1.36 mug/ml, 0.97 +/- 1.20 mug/ml, and 0.49 +/- 0.45 mug/ml, respectively. Despite higher mean sHLA-I levels in malignant and infected patients, no significant difference between these groups was observed (P > 0.05). Generally, the amount of sHLA-I in peritoneal effusions was higher than that for pleural effusions, but the difference was not significant. There were also no statistical differences in the sHLA-I levels between sub-groups of patients with malignancy. EAL cells' killing activity in malignant and infected effusions was 68.15 +/- 11.73 and 78.28 +/- 14.41, respectively (P = 0.08). No correlation between sHLA-I level and NK activity of EAL cells from the patients was found. Almost all malignant cases after exposure to cell-free effusions displayed an increase in NK activity (from 68.66 +/- 11.13 to 74.2 +/- 12.39, P = 0.042) and a decrease in LAK activity (74.5 +/- 18.30 vs 67.72 +/- 16.46, P = 0.040). Whereas, the same experiment performed for non-malignant effusions showed a decrease in both NK activity and LAK activity. Changes in NK and LAK activity were not correlated with the amount of sHLA-I in the effusions. Conclusion: The presence of sHLA-I, particularly in malignant effusions, suggests a role for these molecules in tumor immunity in the peritoneal or plural environment; however, at least with these group of patients, sHLA-I appears not to be a unique determining factor on EAL cells' killing activity.