By co‐culturing regional lymph node B‐cells and HAT‐sensitive mutant cells obtained from RPMI‐1788 cells, no less than 20,000 Epstein‐Barr (EB)‐transformed colonies were obtained from 32 patients with gastric cancer. From B‐cell cultures generating antibodies reactive with gastric cancer tissues as well as cultured gastric cancer cells, two EB‐transformed cell clones termed C418–59 and C1218–39 were isolated. Both of them produced human IgM‐class antibodies, termed Mab418–59 and Mab 1218–39, respectively. Both antibodies reacted with an antigen with a molecular weight of 45 kd existing in gastric cancer MKN‐45, MKN‐1, and Kato‐III cells, and also with all of 4 adenocarcinomas of the stomach in paraffin sections. The antigen recognized by both antibodies was identified as a kind of cytoskeletal protein, cytokeratin 18, In this study, it was confirmed that B‐cell clones generating autoantibodies against cytokeratin 18 were present in some patients with gastric cancer.

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Peripheral blood T-lymphcyte subsets defined by monoclonal antibodies (OKT-series;OKT3: pan T-cell, OKT4: inducer/helper T-cell, OKT8: suppressor/cytotoxic T-cell) were analysed in patients with gastric cancer.The results were as follows.(1) Percentages of OKT3+, OKT4+ and OKT8+ cells as well as the OKT4/OKT8 ratio showed no significant change according to the clinical stages.(2) In recurrent cases, proportion of OKT4+ cells was decreased and that of OKT8+ cells was increased, and the OKT4/OKT8 ratio was reduced, compared with cancer free patients after operation.(3) The OKT4/OKT8 ratio was not correlated with the percentages of IgGFcR+ T-cell (Tr) and ConA/PHA ratio.(4) In patients with high proportion of Tr and low OKT4/OKT8 ratio, the peripheral blood T-cell response to PHA was deminished.(5) The OKT4/OKT8 ratio was remarkably decreased after palliative operation.

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