A monoclonal antibody to human B lymphoblastoid cells activates human and murine T lymphocytes.

A B lymphoblastoid cell line can provide a comitogenic, accessory signal for mitogen-treated T cells. In a study evaluating the antigenic determinant of such cells that mediate this effect, a monoclonal antibody (I57) was raised against the Daudi cell line. This antibody was found to interact with a 30-kDa protein on these cells and had agonistic properties. It enhanced the B lymphoblastoid accessory cell and interleukin 1 (IL-1)-dependent stimulation of PHA-treated murine thymocytes. The stimulatory effect of I57 on PHA-treated thymocytes was more pronounced at high, supraoptimal concentrations of the lectin. This was in contrast with the effect of IL-1 that failed to stimulate these cells treated with PHA at high concentrations. I57 also enhanced stimulation of thymocytes treated with IL-2 alone or with both PHA and IL-2. I57 exhibited by itself mitogenic activity for human T cells. These cells, treated with IL-2, were further stimulated by I57. I57 seems to be different from other agonistic antibodies that have been described so far.