Identification of cultured pleural fluid cells by a direct immunofluorescence technique

A preliminary study demonstrated intracytoplasmic polyvalent immunoglobulin in human pleural fluid cells using a direct immunofluorescence technique. Of 33 pleural-fluid cell samples tested, 31 contained cells that initially stained positive for polyvalent immunoglobulin. The two negative specimens were from malignant effusions. Eleven of the specimens were cultured for seven days; nine of the eleven cultured specimens tested negative for polyvalent immunoglobulin after four days in culture. The remaining two specimens showed a marked decrease in positivity. After adding cell-free pleural fluid to the cultures on day four, the nine negative samples became positive again by day seven; the two slightly positive cases became strongly positive. The significance of these findings is discussed.