Involvement of the transferrin receptor in the production and NK-induced suppression of human antibody synthesis.

Earlier studies have shown that the antibody-secreting lymphoblastoid (LB) B cells which arise in the circulation after immunization can be down-regulated by NK cells and an unusual T suppressor cell. Because the LB B cells require division in vitro before maximal antibody secretion, and as such may express the transferrin receptor, we wished to determine if this receptor is recognized by the NK and/or T suppressor cells. The addition of the antitransferrin receptor antibody B3/25 to cultures of LB cells resulted in a partial inhibition of antibody secretion. This inhibition was not seen with the addition of monoclonal anti-Dr or OKT-8 antisera, and indicated that the LB cells expressed the transferrin receptor and that its activity was required for antibody secretion. The addition of free Fe ions to the culture medium, however, allowed the secretion of antibody by the LB cells even in the presence of B3/25 antibody. Under these conditions, the inhibition of antibody secretion mediated by interferon-activated NK cells was no longer observed. The inhibition induced by pokeweed mitogen-stimulated T suppressor cells was not affected by the antibody treatment, suggesting that these two inhibitory cells recognize different target structures. These results indicate that LB B cells expressed the transferrin receptor at a stage of the in vitro culture, and that this structure is involved in the NK- but not the T cell-mediated inhibition of antibody synthesis.