Interaction of staphylococcal protein A with membrane components of IgM- and/or IgD-bearing lymphocytes from human tonsil.

Abstract

Abstract Human tonsil lymphocytes were examined for their ability to form rosettes with human red blood cells coated with staphylococcal protein A (SpA-HRBC). A significant proportion of cells from unseparated tonsil suspensions were able to form rosettes with SpA-HRBC. Purified T lymphocytes did not form rosettes with SpA-HRBC, whereas in T- cell-depleted suspensions the number of cells forming rosettes with SpA-HRBC was significantly greater than in unseparated populations. After depletion in cells forming rosettes with HRBC coated with anti-human γ-chain immunosorbent-purified rabbit antibodies, a noticeable proportion of B lymphocytes still showed the ability to form rosettes with SpA-HRBC. In addition, when tonsil lymphocyte suspensions were depleted in cells forming rosettes with SpA-HRBC, IgG-bearing cells were no more detectable, but the number of IgM- and of IgD-bearing lymphocytes was markedly reduced in comparison with that found in unfractionated populations. Finally, in tonsil suspensions depleted in IgM- and/or IgD-bearing lymphocytes, the number of cells forming rosettes with SpA-HRBC was significantly reduced in comparison with unfractionated populations and paralleled that of IgG-bearing lymphocytes. The SpA-reacting components present on the membrane of some B lymphocytes were sensitive to treatment with low concentrations of pronase, but other B cells maintained the ability to form rosettes with SpA-HRBC even after treatment with higher pronase concentrations. The membrane components reacting with SpA-HRBC, which were sensitive to the treatment with pronase, were reexpressed by most lymphocytes after 18 hr in culture. The incubation of tonsil lymphocytes with anti-human γ-, but also with anti-human μ- or anti-human δ-chain F(ab’)2 fragments induced a significant decrease in the number of rosettes formed by cells with SpA-HRBC. After incubation of cell suspensions with a mixture of anti-γ-, anti-μ-, and anti-δ-chain F(ab’)2 fragments, virtually no lymphocytes forming rosettes with SpA-HRBC could be found. On the other hand, SpA preincubation of lymphocytes significantly reduced the number of rosettes formed by cells with HRBC coated with either anti-human μ- or anti-human δ-chain F(ab’)2 fragments. These data suggest that SpA interacts with IgG, but also with membrane components strictly related to IgM and/or IgD, present on the surface of a noticeable proportion of B lymphocytes from human tonsil.