Immunoglobulin‐producing cells in the “transitional” mucosa adjacent to adenocarcinomas of the human large bowel

Quantification of IgA‐, IgM‐and IgG‐producing immunocytes was performed in a defined mucosal tissue unit adjacent to 16 adenocarcinomas of the large bowel, and compared with data for control units from 15 histologically normal specimens. The thickness of the “transitional” mucosa adjacent to the tumours was markedly increased. Thus, the average cancer‐associated unit showed a 2.6‐fold increase in height and its number of immunoglobulin‐producing cells was raised 2.8 times. The numerical increase for IgA cells was 2.1, for IgM cells 5.1, and for IgG cells 13.0; the percentage proportions of these cell classes were changed from 91:6:3.6 to 71:12:17. Only very rare IgD‐and IgE‐producing cells were seen. The immunocyte density in 6‐μm‐thick sections (cell number/mm 2 of lamina propria) was 823, 136 and 201 for the IgA, IgM and IgG class, respectively, compared to the normal figures of 1,186, 73 and 49. The density of IgG and IgM cells was thus significantly increased and that of IgA cells decreased in the lamina propria of the “transitional” mucosa. The intra‐individual scatter of all variables, including mucosal height, was large in the “transitional” mucosa, but the variables became normalized approximately 1 cm from the tumour. The excessive rise in the local production of IgG, with no concomitant increase in the density of IgA cells, indicates that there are local stimulatory factors bypassing the secretory IgA immune system. Further studies are needed to show if this local immune response reflects production of tumour‐specific antibodies or is merely due to increased penetrability for antigens from the gut lumen passing through the tumour lesion.