Either 1) the pIgR transcytotic system is differentially regulated in the human body depending on the epithelial tissue (enhancement in the intestines, but not the lungs) or 2) the genotype of either the Calu-3 or Caco-2 carcinoma cell line is altered as compared with the physiological situation in such a fashion that the cells have a lack or gain of expression of (a) certain gene(s) necessary to perform the transcytotic enhancement. The gene discussed is PIGR; the disease is carcinoma.