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A method for rapidly determining levels of T lymphocytes in humans is presented. The method involves staining lymphocytes in peripheral blood or buffy coat smears for acid alpha-naphthylacetate esterase for 1 hr at 37 C. After counterstaining with Wright's stain, the percentage of esterase-positive lymphocytes accurately reflects the percentage of lymphocytes forming E rosettes with sheep erythrocytes.

Ehrlich ascites tumor cells in peritoneal exudate of mice show a more regular round shape, greater and multiple nucleoli and more abundant and dark cytoplasma in comparison with cells of the same tumor transplanted in the limb. In solid tumor cells activity of naphthol-AS-acetate esterase is significantly higher than in exudate cells which demonstrate higher activity of PAS reaction. Other cytochemical reactions show no significant differences between the two cell forms. It seems that exudate cells are biologically more active than cells from the solid tumor.

The indirect leucocyte migration inhibition test was used to investigate production of leucocyte migration inhibitory factor (LIF) by lymphocytes from pleural fluid and peripheral blood. The samples were taken from 19 patients with exudative pleural effusion resulting from malignant disease (n = 9), tuberculosis (n = 5) and nonspecific causes (n = 5). The lymphocytes were cultured in the presence of leucoagglutinin (LA) and purified protein derivative (PPD) and without mitogen or antigen. Although LIF production varied widely, pleural fluid lymphocytes from patients with benign diseases produced significantly more LIF in response to LA than pleural fluid lymphocytes from patients with malignant disease. In comparison to peripheral blood, the LA induced LIF production by pleural fluid lymphocytes was significantly enhanced in patients with nonspecific pleural effusion and significantly reduced in patients with malignant disease. However, pleural fluid lymphocytes from four patients with malignant disease produced LIF spontaneously, suggesting that they were already stimulated in vivo. In tuberculous pleural effusions the percentage of macrophages correlated negatively with the LIF production induced by LA and PPD. Lymphokines produced by sensitized lymphocytes in pleural fluid may be important in the local response to infectious agents and tumour growth by affecting the cellular composition of the effusion.