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G Sobczak

Publications and source records attributed to G Sobczak.

9 recordsLinked to original sources
PubMed1982

Leukemic-like membrane properties acquired by B lymphocytes when depleted of 185,000-dalton macromolecular insoluble cold globulin.

Human peripheral blood lymphocytes can be phenotypically identified by the presence of one or both of two proteins, 225,000-dalton macromolecular insoluble cold globulin (225-MICG) and 185,000-dalton MICG (185-MICG). T cells synthesize and insert into their plasma membrane 225-MICG, null cells 185-MICG, and B cells both 225 and 185-MICG. In contrast, the monoclonal B cells of chronic lymphocytic leukemia are characterized by the presence of 225-MICG and the absence of 185-MICG. We have recently found it possible to chemically deplete 185-MICG from viable normal B cells by treating them with diisopropylfluorophosphate (DFP), thus making normal B cells phenotypically resemble leukemic cells. In the present report we determined whether certain peculiar properties of these leukemic cells would be associated with the normal B cells chemically depleted of 185-MICG. In normal B cells, SIg diffuses in the lipid bilayer to form clusters and caps under appropriate conditions, while in chronic lymphocytic leukemia (CLL) cells this does not occur. Normal B cells depleted of 185-MICG fail to undergo capping of SIg or surface MICG under appropriate conditions. Both DFP-treated B cells and CLL cells tend to rupture when smeared on a glass slide. Both CLL cells and DFP-treated B cells fail to secrete 225-MICG after it has been synthesized intracellularly. The relationship of these findings to the mechanisms of secretion and capping are discussed.

B-Lymphocytes↗
PubMed1981

Chronic lymphocytic leukemia cells lack the 185,000-dalton macromolecular insoluble cold globulin present on normal B lymphocytes.

We have recently characterized two lymphocyte-associated membrane proteins which have been termed 225,000-dalton and 185,000-dalton macromolecular insoluble cold globulin (225-MICG and 185-MICG, respectively) to distinguish their major physicochemical properties. These proteins differ antigenically, structurally, and in their cellular distribution. T cells can be distinguished by the synthesis and presence in the plasma membrane of 225-MICG, Null cells by the appearance of 185-MICG, and B cells by the appearance of both 225- and 185-MICG. The characterization of these two proteins in the monoclonal B lymphocytes of chronic lymphocytic leukemia forms the basis of this report. Using immunofluorescent microscopy, we found only 225-MICG on the surface of chronic lymphocytic leukemia (CLL) cells in 15 patients, whereas control B cells from 20 individuals displayed both 225- and 185-MICG. When MICG proteins were isolated and compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, normal B cells showed two stained bands, corresponding to 225- and 185-MICG, whereas the CLL cells demonstrated only the 225-MICG band. Using labeled amino acid incorporation into cellular protein, normal B cells were shown to synthesize 225- and 185-MICG, whereas CLL cells synthesized only 225-MICG, as determined by immune or cold precipitation of labeled cell lysates. When labeled secretions from B cells and CLL cells were analyzed by immune precipitation, 225- and 185-MICG were secreted by B cells, whereas neither protein was secreted by CLL cells. When normal B cells and CLL cells were mixed, incubated, and lysed together, both 225- and 185-MICG were present, thus excluding proteolysis as a cause of the absence of 185-MICG in CLL. The lack of 185-MICG in CLL distinguishes leukemic cells from normal B lymphocytes. Furthermore, the absence of this normal cell surface protein in these leukemic cells suggests a role for 185-MICG in the malignant transformation of lymphocytes.

B-Lymphocytes↗
PubMed1979

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.

Animals↗
PubMed1979

Macromolecular insoluble cold globulin (MICG): a novel protein from mouse lymphocytes. III. Relationship to the mixed lymphocyte reaction and effect of anti-MICG antiserum in vivo.

In the present communication we have examined the relationship between the synthesis of macromolecular insoluble cold globulin (MICG) and the mixed lymphocyte reaction (MLR). In addition, we have studied in vivo the effect of antiserum to MICG on the antibody response to sheep red blood cells. The experiments indicate that MICG synthesis compared to either IgM or total protein is selectively stimulated in responder T cells exposed to allogeneic stimulator cells in the MLR. Furthermore, cytotoxicity studies utilizing anti-MICG antiserum demonstrated that T cells bearing MICG on their surface are an essential component of the responder cell population in the MLR. In vivo administration of antiserum to MICG significantly suppressed both the primary and secondary antibody response to sheep red blood cells. A possible mechanism for this suppression is discussed.

Animals↗
PubMed1978

A new protein: macromolecular insoluble could globulin (MICG) derived from mouse thymocytes.

A novel protein synthesized and isolated from mouse thymocytes is described. The protein can be separated from radiolabelled cell lysates by taking advantage of its insolubility in the cold. It is a macromolecule with a molecular weight of 225,000 daltons, migrates as a beta-globulin on electrophoresis and has unique antigenic determinents as shown by the production of a monospecific antiserum.

Animals↗