Background: The clinico-biological significance of HLA (both class I antigen and class II one) expressed on tumor cells still remains controversial. Methods: Tumor cells were freshly separated from 33 surgical specimens of pulmonary adenocarcinoma. The tumor cells were incubated for 24 h in the presence or absence of IFN-γ (130 International Units/ml). After incubation, the cells were cytocentrifuged onto glass slides and immunostained with either an anti-HLA class I (A, B, C) monoclonal antibody or anti-HLA class II (DR) one. Results: In 22 of 33 cases (66.7%), the HLA class I were individually expressed by more than 60% of tumor cells while so were the HLA class II in 15 (45.4%). No significant correlation was observed between the HLA class I expression and the HLA class II one. The proportion of HLA class I-positive tumor cells correlated with neither the grade of histological differentiation nor the stage of disease. In contrast, the proportion of HLA class II-positive tumor cells correlated with both the grade of histological differentiation and the stage. In most cases, IFN-γ was found to increase the proportion of class II-positive tumor cells as well as that of class I-positive cells. Conclusions: The above findings thus suggested that the HLA class II expression might therefore represent a manifestation of cellular differentiation and that IFN-γ may, as a result, have the potential to differentiate cancer cells. Copyright (C) 1998 Elsevier Science Ireland Ltd.
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