Lactoferrin and immunoglobulins of the pleural space

The pleural fluids and pleural biopsies of 21 patients have been investigated to delineate defense mechanisms of the pleural space. Lactoferrin (LF), an iron binding bacteriostatic protein, is known to be present in neutrophil leucocytes and almost all mucosal secretions. Using a radioimmunoassay for LF, exudative pleural effusions (protein > 3 G/%, LDH > 200IU) were found to contain 13.8 ± 19.1 μg/ml. Transudate effusions contained 1.4 ± 1.7 μg/ml, P < 0.05. These levels are very similar to those previously found by us in inflammatory and non inflammatory joint fluids, and suggest a simple method of differentiating between the 2 types of pleural effusions. Immunofluorescent staining of parietal pleural biopsies failed to demonstrate LF; the LF in exudates is likely to originate from neutrophils. Immunoglobulin (Ig) levels in effusions were: in exudate effusions (17): IgG: 1.012 ± 434 mg%; IgM: 121 ± 163 mg%; IgA: 210 ± 81 mg%; IgE: 412 ± 1.013 ng/ml; in 4 transudate effusions: IgG: 561 ± 280 mg%; IgM: 70 ± 62 mg%; IgA: 85 ± 59 mg%; IgE: 83 ± 99 ng/ml. P values were: P < 0.05 for IgG; and P < 0.02 for IgA. The Ig levels in exudates are 45-75% of those found in simultaneous serum samples, and did not tend to be higher when the exudate was due to infection. Again, immunofluorescent staining failed to show any Igs in the parietal pleura of any patients. Pleural fluid Igs are likely to be derived passively from serum. One patient with lung adenocarcinoma had a high titre of free secretory component (SC), without a high IgA level, in the pleural exudate. The parietal pleura did not stain by immunofluorescence for SC which is believed to have originated from the tumor cells.