Metabolic characteristics of lymphocyte surface immunoglobulins

Abstract

Abstract Rabbit anti‐mouse globulin reagents at low concentration were attached to the surface of living mouse lymphocytes in the cold. After appropriate washing, the cells were incubated under tissue culture conditions but without C0 2 gassing and the rate of disappearance of the antiglobulin from the cell surface was monitored. Two methods were used, namely, direct labeling with 125 I‐labeled antiglobulin, and sandwich labeling in which the amount of residual antiglobulin at the surface was measured by assessing the degree of binding of a 1251‐labeled sheep anti‐rabbit globulin reagent. Binding of radioactivity to cells was measured both by scintillation counting of washed cell suspensions and by quantitative radioautography. Elution of polyvalent antiglobulin, anti‐k or anti‐μ sera from spleen cells was surprisingly rapid. There was an initial phase of very fast elution and some 30% of counts were lost within 30 min or so, but control experiments showed that this phase was irrelevant to the main experiments. Subsequently, counts were lost more slowly and a reasonable first approximation to the half‐life of Ig receptors on B cells was 2 h. In contrast, lymphocyte surface H‐2 antigen and the receptors to which anti‐lymphocyte globulins attach were much more stable. A number of control experiments suggested that anti‐Ig reagents were shed from the cell surface by true metabolic turnover of B cell receptors, and not by antigen‐ antibody uncoupling or anti‐receptor‐induced extrusion. It was strongly suggested that some pinocytosis of attached antiglobulin occurred, but that this was not the major source of anti‐receptor loss. Shed receptors were continually regenerated, and the process of shedding was shown to be dependent on lymphocyte metabolic activity. Thymus lymphocyte surface Ig also turned over, but at a rate considerably less than that for spleen cells. A continuous, gentle leakage of Ig from the B lymphocyte surface was deemed to have important theoretical implications. These included a logical source of much natural antibody, increased emphasis on the multi‐hit nature of both immune induction and tolerance induction, a plausible explanation for the necessity of multi‐point binding of antigens to B cells in activation and a rationale for the fact that many adoptive immune responses require active immunization of the host animal.