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Biomedical subjects

G T Stevenson

Publications and source records attributed to G T Stevenson.

16 recordsLinked to original sources
PubMed1979

Antibody-induced changes in levels of cyclic adenosine monophosphate in leukaemic lymphocytes.

When L2C leukaemic B lymphocytes from guinea-pigs were incubated in vitro with antibody directed to their surface immunoglobulin (Ig), a rapid rise in intracellular adenosine 3':5'-phosphate (cyclic adenosine monophosphate, cAMP) was observed. Estimation of cAMP was by a protein-binding assay using bovine adrenal protein kinase. Increases up to 30-fold occurred within 30 seconds of incubation at 37 degrees C, to be succeeded by a fall which reached the basal level between 5 and 7 min. The response was proportional to the amount of antibody present. Cross-linking of surface Ig by the antibody was necessary, bivalent (Fab'gamma)2 from the antibody gave a rise in cAMP similar to that given by the parent molecule, whereas monomeric Fab'gamma was ineffective unless it was subsequently cross-linked by anti-antibody. The rise was too rapid to have required capping of the surface Ig for its induction. Not all perturbations of the plasma membrane by antibody induce such a surge in cAMP, since anti-beta2 microglobulin, also reacting with the lymphocyte surface, failed to alter cAMP concentration. The results emphasize that immunotherapy can be influenced by antibody altering the metabolic activity of target cells, quite apart from activation of immunological cytotoxic pathways.

Animals↗
PubMed1978

beta2-Microglobulin from normal and leukaemic guinea-pig lymphocytes.

beta2-Microglobulin has been isolated in useful quantities from the urine of strain-2 guinea-pigs after either treatment with sodium chromate or induction of the L2C leukaemia. Antibodies raised against the beta2-microglobulin were used to set up a radioimmunoassay which measured its export into culture fluid by normal and leukaemic lymphocytes. Material containing beta2-microglobulin was also obtained by digestion of the lymphocytic surfaces with papain; fractionation demonstrated both free and combined forms, with no qualitative difference between those from normal and those from leukaemic cells.

Animals↗
PubMed1978

Synergistic cytotoxic effects of antibodies directed against different cell surface determinants.

Three antibody populations were raised in rabbits against surface antigens on guinea-pig L2C leukaemic lymphocytes: against idiotypic determinants on the lambda chain of the surface immunoglobulin, against C region determinants on the lambda chain, and against the surface antigens recognized by conventional anti-lymphocyte sera. Complement and K-cell cytotoxicities effected by the antibodies on L2C cells were studied in vitro. In both cytotoxic systems mixtures of the antibodies revealed synergy, in that the titres of the mixtures exceeded predicted additive titres of their components. The synergy was greater when the mixed antibodies were directed to determinants on the same molecule rather than to determinants on different molecules.

Animals↗
PubMed1978

Further studies of immunoglobulin synthesis by guinea pig leukaemic lymphocytes.

The L2C leukaemia is a B-lymphocytic neoplasm of strain 2 guinea-pigs, maintained by passaging in vivo. It synthesizes mu and lambda immunoglobulin chains. These combines to form monomeric (7S) IgM molecules which are inserted into the plasma membranes. From here they are shed as monomeric IgM and as a species of higher molecular weight which has not been further defined. The synthesis of lambda chain is in excess of that required for the IgM molecule, the surplus being exported directly from the cell without any intervening phase in the plasma membrane. Quantitative estimates of synthetic rates and pool sizes for these immunoglobulin species are presented.

Animals↗
PubMed1977

Proteolysis of lymphocytic surface immunoglobulin.

Limited proteolysis of lymphocytic surface immunoglobulins in guinea-pig, rabbit and man was investigated by immunofluorescence using conjugated antisera specific for immunoglobulin fragments. The cell surface IgM of guinea pig L2C leukaemic lymphocytes and rabbit blood lymphocytes was cleaved in situ at its hinge region by papain. The Fcmicron fragment remained attached to the membrane and could be stained with the appropriate anti-Fc conjugate. The surface IgD and IgM of human chronic lymphocytic leukaemia cells was cleared from the cell surface by papain, as shown by reagents directed against both Fab and Fc region determinants. This could be due either to proteolytic degradation of membrane bound Fc or to initial cleavage of Ig from the membrane at some point other than the hinge region.

Animals↗
PubMed1977

Some effects on leukaemic B lymphocytes of antibodies to defined regions of their surface immunoglobulin.

During the growth of the L2C leukaemia in strain 2 guinea-pigs there is excreted in the urine a monoclonal light chain of lambda class. This is believed to arise from synthesis by the leukaemic cells of a small molar excess of the light chains incorporated into their surface IgM. Antibodies to this light chain have been raised in rabbits and separated by immunosorption into those directed against idiotypic determinants (anti-Id), and those against determinants also present on other lambda chains (anti-lambda). Both antibodies react with L2C cells via the surface immunoglobulin. In accord with prediction anti-Id is specific for L2C cells while anti-lambda also reacts with 7 per cent of normal nodal lymphocytes. L2C cells are agglutinated strongly by anti-Id, weakly by anti-lambda. Both antisera inhibit migration of the cells, and both can kill them by invoking complement or K-cell cytotoxic mechanisms. The results emphasize the potential of anti-idiotype sera for identifying and specifically attacking neoplastic B lymphocytes.

Animals↗
PubMed1976

Anti-idiotype sera raised against surface immunoglobulin of human neoplastic lymphocytes.

The idiotypic determinants of surface immunoglobulins on B-cell lymphomas and lymphocytic leukemias represent tumor-specific antigens, individually unique for each tumor. As such they have both diagnostic and therapeutic potential, particularly for those neoplasms with no serum monoclonal immunoglobulin arising from synthesis of the protein for export. We describe the raising in animals of anti-idiotype sera directed against two examples of a nonexporting neoplasm, human chronic lymphocytic leukemia. The procedure involves exposing the cells to papain so as to remove the Fab fragments (containing the idiotypic determinants) from the surface immunoglobulin, recovering the Fab on cellulose immunosorbent particles, and immunizing animals with the immunosorbent-Fab complex.

Aged↗
PubMed1975

The specificity of a solid phase radioimmunoassay for human immunoglobulins.

The specificity of a solid phase radioimmunoassay for immunoglobulin antigens, human Fab-mu in the case illustrated, has been assessed. The anti-Fab-mu serum available reacted well on gel diffusion with all Fab-mu- and light chain-containing proteins. In contrast the radioimmunoassay, in which unlabelled test antigen competes with radiolabelled Fab-mu for anti-Fab-mu coupled to Sephadex beads, was sensitive only to proteins containing entire Fab-mu regions. A double antibody radioimmunoassay showed comparable or greater sensitivity for Fab-mu-containing proteins, but was much less specific. By using Fab-gamma as the labeled antigen, with only light chain determinants reacting with the anti-Fab-mu, the solid phase assay was rendered polyspecific in being sensitive to all proteins containing light chain. Reasons for the specificity of the solid phase assay are discussed: steric factors can be expected in some cases to permit strong binding of antigen by multiple bonds, in others to restrict the number of molecular determinants simultaneously available to antibody.

Ammonium Sulfate↗
PubMed1975

A gamma Bence-Jones protein in guinea pigs.

1. The L2C lymphocytic leukaemia in strain-2 guinea pigs is accompanied by a protein in the urine resembling a homogenous immunoglobulin light chain. 2. The amino acid sequence over the first 20 residues demonstrates a close analogy with a human gamma chain of V region subgroup IV. 3. The protein is apparently synthesized by the leukaemic cells and thus represents a monoclonal light chain, i.e. a Bence-Jones protein.

Amino Acid Sequence↗
PubMed1975

Surface immunoglobulin of guinea-pig leukaemic lymphocytes.

The surface immunoglobulin of the transplantable L2C leukaemia of strain 2 guinea-pigs has been investigated. The immunoglobulin is seen to be synthesized when the cells are maintained in culture, indicating its intrinsic origin. Immunolabelling of the cell surface and immunochemical study of the Fab released by limited surface proteolysis indicate the presence of immunoglobulin of class IgM. IgG and free light chains were not detected, and there is unlikely to be an appreciable amount of immunoglobulin of any other class. The amount of immunoglobulin present, in terms of 4-chain monomers, is approximately 100,000 molecules per cell. Its half-life, calculated from the rate of reappearance in vitro of surface Fab after proteolytic clearing, is approximately 5 hours. Immunoglobulin secreted into the environment appears to arise predominantly or entirely from the cell surface: there is no evidence of an appreciable export of immunoglobulin which does not have a surface phase. Papain at 0.06 mg/ml rapidly removes the surface Fab. Residual Fcmu can then be detected by immunofluorescence, suggesting that papain cleaves surface IgM at a hinge region with the molecule in situ on the membrane. The released Fab is only moderately susceptible to degradation by papain at the enzyme: substrate ratio prevailing. It has been possible to isolate it from the papain digest by immuno-adsorption, with a notional yield of 75 mug per 10-10 cells, and then to prepare antisera against it.

Animals↗