Human macromolecular insoluble cold globulin (MICG). II. Immunologic definition of T cell and null cell MICG and the biologic effect of antiserum to MICG.

Thymus cell-derived macromolecular insoluble cold globulin (T-MICG) is a 225,000-dalton protein, selectively synthesized in human T cells. Null cell-derived macromolecular insoluble cold globulin (N-MICG) is a 185,000-dalton protein, synthesized in null cells, and antigenically distinct from T-MICG. Evidence to support these conclusions was provided by using isolated cell preparations that were radiolabeled, lysed in desoxycholate, and precipitated with monospecific antiserum to each component. These studies demonstrated that antiserum to T-MICG precipitated a 225,000 dalton protein from PBL and T cells, but not from B or null cells. Antiserum to N-MICG reacted with a 185,000 dalton protein present in PBL and null cells, but not with lysates from either T or B cells. The plasma membrane distribution of these proteins was shown by absorption of antiserum to T + N-MICG with either isolated T or null cells. Antibody-induced cytotoxicity and immunofluorescence confirmed the cell surface location of T and N-MICG. Divergent biologic effects of these antisera were also noted. Antiserum to T-MICG inhibited T cell rosette formation and the one-way mixed lymphocyte reaction, although anti-N-MICG antiserum had no such effect. The potential importance of these proteins is discussed.

Human macromolecular insoluble cold globulin (MICG). I. T-cell origin of T-MICG and null cell origin of N-MICG.

Although surface immunoglobulin characterizes B cells in man, there are few surface markers that distinguish T cells. We have described a new protein synthesized in human T cells, termed T-MICG. This protein is a macromolecule of 225,000 daltons, is insoluble in the cold, and migrates as a beta-globulin on electrophoresis. Separation of human peripheral blood lymphocytes into T and B-cell populations by rosette sedimentation and anti-human-Fab columns clearly demonstrated the T-cell origin of the 225,000 dalton component. Furthermore, null cells were shown to synthesize a protein of 185,000 daltons, termed N-MICG, with physical properties similar to T-MICG, T-MICG and N-MICG were shown to be antigenically dissimilar, employing antiserum to each of these proteins. The present studies demonstrate two novel cell surface markers, T-MICG and N-MICG, which characterize T cells and null cells, respectively.