Inhibition of T-lymphocyte rosetting by HL-A alloantisera and complement.

Abstract

The relationship between HL-A antigens and rosetting of sheep red blood cells (SRBC) with peripheral human lymphocytes has been investigated by incubating them with HL-A antibodies. Although sensitizing the lymphocytes with HL-A alloantisera had no effect on their ability to form rosettes with SRBC, further sensitization with C6 deficient rabbit serum as a source of early complement components inhibited the formation of rosettes with SRBC. The involvement of HL-A alloantibodies in the inhibition of rosette formation was shown first by correlating the HL-A phenotype of the lymphocytes and the HL-A specificity of the alloantisera and, second, by specifically absorbing the HL-A alloantibodies from the alloantisera. Complement was needed to inhibit rosette formation since this effect was lost when rabbit serum was treated to inactivate complement. The participation of complement's classical pathway in rosette inhibition was shown by chelating the Ca2+ ions by EGTA treatment of the C6 deficient rabbit serum. Perhaps, binding of HL-A antibodies and early complement components to the lymphocyte surface disturbs the distribution of the receptors or affects the charge of the cell membrane, thus inhibiting the rosette formation with SRBC.