Antigen-specific t lymphocyte clones. II. Purifcation and biological characterization of an antigen-specific suppressive protein synthesized by cloned T cells

Abstract

We have generated an antigen-specific T suppressor clone that synthesizes 70,000-mol wt peptides that have antigen-specific-binding activity. Although these data also indicated that antigen-binding peptides completely inhibited the in vitro primary response to a complex antigen, suppression might reflect the combined biologic activities of many different 70-mol wt polypeptides or polypeptides associated with the 70,000-mol wt material by noncovalent interactions. The protein responsible for antigen-specific suppression was therefore purified to virtual homogeneity after sequential separation of internally labeled supernate peptides on Sephacryl S-200 and DEAE-cellulose columns followed by isoeleetrofocusing. The resulting protein is greater than 95 percent homogeneous according to sodium dodeeyl sulfate-polyacrylamide electrophoresis and represents two peptides having two very close but distinguishable isoelectric point values of approximately 5.0. The purified molecules are retained by columns coated with lentil lectin or antigen but not by columns coated with antisera specific for immunoglobulins, the I region of the major histocompatibility complex or Ly-1 or Ly-2 antigens. Less than 50 pg of the purified glycoprotein specifically and completely suppresses production of anti-sheep erythrocyte plaque-forming cell by mixtures of 10(6) Ly-1 cells and B cells and this is a result of inactivation of Ly-l-mediated helper function. Specific inactivation of T (Th) cells by the 70,000-mol wt molecule is rapid, specific, and requires the presence of antigen. The mechanism of specific suppression of Th function may depend upon two functionally distinct regions of the 70,000-mol wt molecule: one that binds antigen and a second that mediates suppression.

Antigen-specific T lymphocyte clones. III. Papain splits purified T suppressor molecules into two functional domains.

“…The Ts clone CI.Ly23/4 secretes a 70,000-tool wt glycoprotein that binds specifically to glycophorin from SRBC and specifically suppresses the primary antibody response to SRBC (5,6). Metabolically labeled proteins (50,000 cpm) from the supernatant of this clone were incubated for 2 h with SRBC or BRBC.…”

“…Biosynthetic labeling of the 70,000 tool wt protein and purification of this protein to homogeneity from supernatant material has been described in detail (5,6).…”

“…Inhibition of anti-RBC helper function was tested as described previously (5,6). Briefly, 10 Ly-1 helper cells from SRBC-or BRBC-immune donors were incubated with different proteins for 6-72 h. Cells were then washed with PBS and tested for specific RBC helper activity after addition to cultures containing 106 B cells and the homologous erythrocyte.…”

“…We have defined a clone of Ly-2 ÷ T-suppressor (Ts) 1 cells that expresses cell-bound receptors for antigen and secretes a 70,000-tool wt glycoprotein that specifically binds to antigen and mediates antigen-specific suppressor activity. It is likely that the secreted protein represents a modified form of the cell-bound receptor, as is the case for B cells (5,6).…”

“…T cell clones can synthesize homogeneous proteins that mediate T cell recognition and function (1)(2)(3)(4)(5)(6). We have defined a clone of Ly-2 ÷ T-suppressor (Ts) 1 cells that expresses cell-bound receptors for antigen and secretes a 70,000-tool wt glycoprotein that specifically binds to antigen and mediates antigen-specific suppressor activity.…”