Receptors for IgG (Fc receptors) on human lymphocytes: re-evaluation by multiple techniques

This study examines whether receptors for IgG (Fc receptors), as identified by different methods, are found on identical human lymphocyte subpopulations, and the relationship of Fc receptors to surface immunoglobulin (SIg) and receptor for complement (C'). Fc receptors were identified by two rosetting techniques (antibody-sensitized human erythrocytes, HuEA, or sheep erythrocytes, ShEA) and two immunofluorescent techniques (heat-aggregated IgG of human origin, HuAgg, or of guinea-pig origin, GPAgg).

When lymphocytes depleted of cells rosetting with ShEA were compared to HuEA-depleted lymphocytes, the two subpopulations appeared to be significantly different. However, when lymphocytes were depleted of cells rosetting with ShEA which had been sensitized with lower concentrations of antibody, the subpopulation so depleted appeared to be virtually identical to HuEA-depleted lymphocytes. These studies suggest that more than one lymphocyte subpopulation has Fc receptors and that each subpopulation can, in part, be identified and distinguished from the other by the capacity to bind IgG at differing concentrations.

In particular, these experiments may serve to resolve the controversy concerning the presence of Fc receptors on lymphocytes bearing surface immunoglobulin (SIg). Depletion of lymphocytes rosetting with ShEA removed most of the SIg-bearing lymphocytes; depletion of cells rosetting with ShEA which had been sensitized with lower concentrations of IgG antibody, however, failed to deplete SIg-bearing lymphocytes even though other Fc-bearing populations were completely depleted. These results suggest that SIg-bearing lymphocytes (B lymphocytes) do have Fc receptors but that high concentrations of IgG are needed to demonstrate them.