M. Rossel et al., NONSPECIFIC INCREASED SERUM LEVELS OF SECRETORY COMPONENT IN LUNG-TUMORS - RELATIONSHIP TO THE GENE-EXPRESSION OF THE TRANSMEMBRANE RECEPTOR FORM, American journal of respiratory cell and molecular biology, 9(3), 1993, pp. 341-346
Polymeric immunoglobulin receptor (pIg-R) is synthesized by epithelial
cells lining the bronchial mucosa. It is released in secretions as fr
ee 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 tumor
markers, we measured SC and secretory Ig, using enzyme-linked immunos
orbent assay, in the serum of 45 patients with lung carcinomas, in the
serum of 10 patients with non-neoplastic diseases, and in the serum o
f 45 control subjects. We also studied the immunohistochemical express
ion of pIg-R and its mRNA in tumors from 20 out of the 45 patients. Se
rum levels of SC and S-IgA were similarly and significantly elevated i
n patients with lung cancer (squamous cell carcinoma [25 cases], small
cell carcinoma [7 cases], adenocarcinoma [13 cases]) and with non-neo
plastic diseases, as compared with control subject levels (P < 0.001).
The highest SC levels were found in patients with adenocarcinoma alth
ough the mean SC level was not different from other pathologic conditi
ons. pIg-R was usually not detected in the cells of small cell carcino
ma or of squamous cell carcinoma, whereas it was found in the cells of
five adenocarcinomas and in the two in situ carcinomas under study. T
he specific mRNA analysis usually agreed with the immunolocalization o
f pIg-R. A single band at 3.8 kb was detected in the positive tumor ti
ssues and in normal lung tissues. However, the signal was weak in one
case of squamous carcinoma and stronger in two out of three adenocarci
nomas, than in normal tissues. Seven transplanted tumors, developed in
nude mice from the metastases of adenocarcinoma (three cases), small
cell carcinoma (one case), and squamous cell carcinoma (three cases),
were negative for pIg-R and its mRNA expression. We concluded that hig
h serum levels of SC were not specific for lung tumors and that SC was
secreted mainly by normal lung tissue in contact with tumor cells, ex
cept in adenocarcinoma where tumor cells synthesized pIg-R. High pIg-R
mRNA levels and pIg-R expression could be considered characteristic f
eatures of adenocarcinomas. The preserved expression of both pIg-R and
its mRNA in cells of in situ squamous cell carcinoma, and expression
of a weak expression of the pIg-R RNA only, in some of the squamous ce
ll carcinomas, could indicate intermediate stages of cell differentiat
ion.