Mechanism of binding of soluble immune complexes to lymphocytes

Soluble immune complexes prepared with either (a) ¹²⁵I BSA and mouse antiserum to BSA in the presence of fresh mouse serum (AgAbC) or with (b) ¹²⁵I BSA and a 7S fraction of the mouse antiserum to BSA (AgAb) bind to a certain proportion of mouse lymph node and spleen lymphocytes (but not to thymocytes). The efficiency of binding is greater when complexes are prepared at defined antigen/antibody ratios and when the incubation with lymphocytes is performed at 37 °C. However, a significant degree of binding occurs at lower temperatures and even at 0 °C. Cells which bind soluble complexes overlap extensively with complement receptor lymphocytes (CRL) (B lymphocytes) since the specific elimination of CRL also depletes the population of cells which can bind soluble complexes. Two types of interactions are involved in the binding: one mediated by antibody which has been aggregated by antigen and another by complement (probably C3). They can be operationally distinguished because (1) after treatment of the lymphocytes with trypsin, the binding of AgAbC (but not of AgAb) is strongly inhibited; (2) the binding of AgAb (but not of AgAbC) is inhibited by heat-aggregated Ig; (3) the binding of AgAbC (but not of AgAb) to lymphocytes inhibits their subsequent interaction and rosette formation with erythrocytes sensitized by antibody and complement components; and (4) cobra venom factor markedly alters the binding of AgAbC to lymphocytes.