Protein A Reactivity of Lymphocytes from Some Patients with Chronic Lymphocytic Leukaemia Mediated by an Interaction with the F(ab')2 Region of Surface Immunoglobulin

Peripheral blood lymphocytes (PBL) from 15 of 38 patients with chronic lymphocytic leukaemia (CLL) were capable of forming rosettes with human erythrocytes coated with staphylococcal protein A (SpA-HRBC). PEL from seven patients also showed a marked proliferafive response after stimulation with Staphylocccus aureus bacteria strain Cowan I (Cowan Staph). The SpA-rosetling of CLL cells was inhibited by incubation with F(ab')2 fragments of anli-immimoglobuiin (Ig) antibodies. In addition, incubation with these fragments inhibited the proliferative response of leukacmie B cells to Cowan Staph. The Cowan-Siaph-induced proliferation of CLL cells was also impaired by the addition of normal human IgG and human IgG F(ab')2 fragments to the cultures, whereas non-immune rabbit IgG was not inhibitory, The inhibitory activity of human IgG F(ab')2 fragments was retained hy a SpA-Sepharose column, and it was found in the material recovered from the same column by acid elution. These data indicate thai an interaction between SpA and a structure located in the F(ab')2 region of surface Ig of different classes is responsible for either SpA-binding or the Cowan-Staph-induced proliferate response of PBL from some patients with CLL.