AbstractThe proliferative and plaque-forming cell (PFC) responses of unseparated mononuclear cells (MNC) and B- and T-cell-enriched populations of cells were analyzed in 15 patients with lung cancer to determine the mechanisms involved in the functional abnormality of their B cells. The PFC responses of the MNC of the patient group were significantly lower than those of normal controls. In addition, the enriched B cells of several patients showed a further decrease in their PFC responses after coculture with autologous Tcells compared with their respective MNC responses. The proliferative response against phytohemagglutinin (PHA) was also lower in many of the patients after similar cocultures. Cocultures of patients' B cells with T cells from normal controls significantly enhanced the PFC responses in 7 patients. In most of the normal controls, B lymphocytes showed a significant decrease in their PFC responses after coculture with the patients' T cells. Although the percentages of total T cells, T-helper, and B cells were within the normal range, the number of suppressor T cells was significantly higher in the patient group. These results indicate that a combination of insufficient T-cell help, excessive suppression by both T and non-T cells, and a possible intrinsic B-cell abnormality are responsible for the B-cell functional deficiency observed in patients with lung cancer.