Arming of lymphoid cells by IgG antibodies treated with protein A from Staphylococcus aureus.

Mouse spleen lymphocytes treated with rabbit IgG anti-sheep erythrocytes (SRBC) complexed with protein A of Staphylococcus aureus (SpA) form rosettes with SRBC. The attachment of SRBC to lymphocytes was due to the binding of the SpA-IgG antibody complex to the surface of the lymphocytes and was thus considered "arming" of the cells. Normal mouse spleen cells "armed" with SpA-rabbit IgG anti-chicken erythrocytes (CRBC) kill specifically 51Cr-labeled CRBC "in vitro" in the absence of free antibodies. The killing by these "armed" cells is an effect of the cell-bound SpA-IgG antibody complex. Both the SRBC rosette formation and the cell-mediated CRBC killing was dependent on the concentration of the SpA-IgG antibody complexes used for "arming" the cells. A 100-fold increase in rosette formation or in killing of target cells was recorded for lymphocytes treated with SpA-IgG antibody complexes in comparison with cells treated with noncomplexed IgG antibodies. The specific binding of SpA-IgG antibody complexes to the Fc receptors of mouse spleen cells was demonstrated by inhibition studies. More than 60% inhibition of the rosette formation and in the killing of target cells was shown for cells treated with normal rabbit IgG or its Fc fragment before addition of the SpA-IgG antibody complex.