Polymeric immunoglobulin receptor (pIg-R) is synthesized by epithelial cells lining the bronchial mucosa. It is released in secretions as free
secretory component (SC) or bound to Ig as secretory Ig (S-
IgA and S-
IgM). To evaluate the usefulness of SC and pIg-R expression as tumour markers, we measured SC and secretory Ig, using
enzyme-linked
immunosorbent assay, in the serum of 45 patients with lung
carcinomas, in the serum of 10 patients with non-neoplastic diseases, and in the serum of 45 control subjects. We also studied the immunohistochemical expression of pIg-R and its
mRNA in
tumors from 20 out of the 45 patients. Serum levels of SC and S-
IgA were similarly and significantly elevated in patients with
lung cancer (
squamous cell carcinoma [25 cases],
small cell carcinoma [7 cases],
adenocarcinoma [13 cases]) and with non-neoplastic diseases, as compared with control subject levels (P < 0.001). The highest SC levels were found in patients with
adenocarcinoma although the mean SC level was not different from other pathologic conditions. pIg-R was usually not detected in the cells of
small cell carcinoma or of
squamous cell carcinoma, whereas it was found in the cells of five
adenocarcinomas and in the two in situ
carcinomas under study. The specific
mRNA analysis usually agreed with the immunolocalization of pIg-R. A single band at 3.8 kb was detected in the positive
tumor tissues and in normal lung tissues. However, the signal was weak in one case of
squamous carcinoma and stronger in two out of three
adenocarcinomas, than in normal tissues.(ABSTRACT TRUNCATED AT 250 WORDS)