Expression of Fc_ϵ receptors on activated human T lymphocytes

Our results clearly demonstrate that the low‐affinity receptor for IgE (Fc_ϵR) is an activation antigen transiently expressed on a subpopulation of human T lymphocytes. It can be selectively induced by stimulation with certain antigens or lectins, but it is not found on resting T cells. The increased numbers of activated Fc_ϵR⁺ T cells observed after stimulation of peripheral blood mononuclear cells (PBMC) from bee venom allergic patients with the specific allergen phospholipase A₂ (PLA₂) suggest that Fc_ϵR⁺ T cells might very well be involved in the regulation of the human IgE response against the respective antigen. These results were obtained by the use of two monoclonal antibodies, M‐L25 and M‐L47, which were raised against the human low‐affinity Fc_ϵR in our laboratory. After stimulation of PBMC with phytohemagglutinin a peak of 7,6 ± 6% Fc_ϵR⁺ T cells was observed on day 3, with pokeweed mitogen of 0.8 ± 0.8% on days 2 and 3, and with concanavalin A of 0.6 ± 0.7% Fc_ϵR⁺ T cells on day 2. Stimulation of PBMC with tetanus toxoid (TT) induced Fc_ϵR on maximally 0.6 ± 0.8% of the total T cells (day 4), stimulation with purified protein derivative from tuberculin (PPD) on 0.2 ± 0.6% of the T cells (day 2). In contrast to these antigens, stimulation of PBMC from bee venom allergic patients with PLA₂ induced as a peak 2.5 ± 2.5% of the total T cells to express Fc_ϵR (day 5), although the stimulated T cell population was much smaller than with TT or PPD, as was shown by their stimulation indices. The allergen‐stimulated Fc_ϵR⁺ T cells were exclusively T4⁺. The Fc_ϵR‐expression index was determined, which for a specific antigen or lectin correlates the percentage of Fc_ϵR⁺ T cells to the stimulated T cell population, respectively.