IgA-specific helper activity of T alpha cells in human peripheral blood.

A subpopulation of human T lymphocytes that express receptors of immunoglobulin A (T alpha cells) was separated by a FACS using FITC-conjugated human IgA myeloma protein in order to determine whether they have helper activity for in vitro immunoglobulin synthesis in comparison with a T alpha cell population separated by rosette formation using PTN-ORBC conjugated with MOPC-315 mouse IgA myeloma protein. FACS-separated T alpha cells have IgA specific helper activity, whereas rosette-separated T alpha cells have polyclonal helper activity for in vitro immunoglobulin synthesis in PWM-stimulated B cells. The polyclonal helper activity observed in rosette-separated T alpha cells might be due to contamination of non-T alpha cells in the T alpha cell fraction. It is concluded that purified T alpha cells in normal human peripheral blood show IgA-specific helper activity in vitro.