PubMed Health⌕ Search

Biomedical subjects

K Balakrishnan

Publications and source records attributed to K Balakrishnan.

At least 55 records · Page 3Linked to original sources
PubMed1984

The effect of donor-specific transfusions on rat heart allograft survival.

A rat heart allograft model employing donor-specific transfusions (DSTs) was used to investigate several questions relevant to their clinical usage. The effects of varying blood storage duration (stored vs. fresh), number and timing of DSTs as well as use of concomitant azathioprine and cyclosporine (CsA) were assessed in terms of allograft survival and recipient sensitization. A comparison of stored and fresh-blood DSTs revealed that blood stored for up to 5 weeks was as effective as fresh blood and that a 2-week storage was optimal. Increased storage appeared to be associated with decreased sensitization. Multiple DSTs were more effective than a single DST and the peak effect appeared after six. Transfusions given at the time of transplantation were ineffective. The addition of concomitant (preoperative) azathioprine or CsA resulted in a further decrease in sensitization but also resulted in a dose-dependent diminution of the transfusion effect.

Animals↗
PubMed1983

A simple and rapid method for the preparation of plasma membranes.

A simple and rapid method for preparing plasma membranes from isolated cells or tissues is described. The membranes were characterised (a) biochemically by an analysis of specific marker enzymes, (b) by quantitation of cell surface receptors, and (c) immunologically by their ability to elicit specific allogeneic responses from cytotoxic T cells in secondary in vitro stimulations. Based on both biochemical and immunologic criteria, plasma membranes prepared by the method described here are of equal or greater 'purity' compared to those prepared by two other methods that are most widely used to date and the yields are several-fold higher.

Animals↗
PubMed1983

Fusion and biochemical expression of membrane receptors in foreign living cells.

Successful transplantation of cell surface molecules from the membranes of one cell type to recipient cells of a different type is described. Plasma membranes purified from donor cells were fluoresceinated and fused to recipient cells using poly(ethylene glycol) and the fate of the transplanted membrane components was followed by fluorescence microscopy. In approximately 100 min the 'foreign' membrane components were seen to cluster and internalise. During this time, judged by the criteria of hormonal stimulation and immune cytotoxic killing, the cell surface of the recipient cell mimicked the cell surface phenotype of the donor cell.

Adenylyl Cyclases↗
PubMed1982

Monoclonal antibodies to a nitroxide lipid hapten.

The isolation and characterization of a hybridoma cell line producing a monoclonal IgG1 antibody against a spin-label nitroxide group is described. The antibody recognizes a synthetic hapten containing linked dinitrophenyl and 2,2,6,6-tetramethylpiperidinyl-1-oxy groups, having an affinity of 3.6 +/- 1.0 . 10(6) M-1 for the soluble hapten at 25 degrees. The antibody binds to phospholipid vesicles containing 2 mol% of spin label-derivitized lipid (lipid hapten) with an affinity of 1.5 +/- 0.2 . 10(8) M-1. This monoclonal IgG1 mediates the binding of hapten-bearing lipid vesicles to mouse macrophage RAW264 cells bearing Fc receptors. The cellular responses to this binding are similar to those observed previously using polyclonal rabbit anti-hapten IgG. As with the heterogeneous antibodies, the monoclonal IgG1 is more efficient in mediating cellular uptake when the vesicles are in the "fluid' physical state (dimyristoylphosphatidylcholine at 37 degrees C) compared to "solid' (dipalmitoylphosphatidylcholine at 37 degrees C). Despite the enhanced binding of "fluid' phospholipid vesicles to cells, only the "solid' vesicles triggered a significant respiratory burst in Raw264 macrophages.

Animals↗
PubMed1982

Lipid hapten containing membrane targets can trigger specific immunoglobulin E-dependent degranulation of rat basophil leukemia cells.

We have studied the binding of liposomes containing dinitrophenylated lipid to rat basophil leukemia cells armed with monoclonal anti-dinitrophenyl IgE. The liposomes were either "fluid" at 37 degrees C (dimyristoylphosphatidylcholine or an equimolar binary mixture dipalmitoylphosphatidylcholine and cholesterol) or "solid" (dipalmitoylphosphatidylcholine, distearoylphosphatidylcholine, or dibehanoylphosphatidylcholine). We have also studied the immune mediated degranulation of these cells induced by the above lipid membrane targets. In some cases both studies were carried out with liposomes containing various surface densities of lipid haptens. From these studies we conclude that freely mobile nonaggregated lipid haptens in bilayer membrane targets can trigger efficient serotonin release from rat basophil leukemia cells in the presence of specific antihapten IgE. Solid target membranes are also effective as stimulators of serotonin release. The release of serotonin depends strongly on the surface density of lipid haptens over a narrow range of surface densities. These studies with lipid membrane targets having well defined physical properties indicate the need for generalized molecular models of receptor-mediated cell triggering.

Animals↗
PubMed1982

Availability of dinitrophenylated lipid haptens for specific antibody binding depends on the physical properties of host bilayer membranes.

We have measured the binding of two radioiodinated monoclonal anti-dinitrophenyl antibodies (IgE and IgG2a) to two dinitrophenylated lipid haptens in lipid bilayer membranes having various compositions and physical properties. These antibodies bind strongly to the lipophilic dinitrophenyl group in some membranes. Dimyristoylphosphatidylcholine and dipentadecanoylphosphatidylcholine containing 2 mol % dinitrophenyl lipid hapten bind anti-dinitrophenyl antibodies below the chain-melting transition temperatures of these lipids (22 and 35 degrees C, respectively) but not above these temperatures. Evidently, the lipophilic dinitrophenyl group is partially or completely buried in the hydrophobic region of these bilayers at temperatures above the chain-melting transition temperatures. The inclusion of increasing concentrations of cholesterol in such membranes (e.g. in dimyristoylphosphatidylcholine at 37 degrees C) results in a marked enhancement of antibody binding. It was found that a third lipid hapten containing the dinitrophenyl group does not show this strong dependence of antibody binding on the physical state of the lipid membrane. The weak immunologic degranulation of rat basophil leukemia cells by dimyristoylphosphatidylcholine membrane targets at 37 degrees C can be attributed to a weak binding of anti-dinitrophenyl IgE to these membranes (Balakrishnan, K., Hsu, F. J., Cooper, A. D., and McConnell, H. M. (1982) J. Biol. Chem. 257, 6427-6433). However, if the antibody is first allowed to bind to this membrane below the lipid chain-melting transition temperature, these IgE-coated membrane targets are very effective in releasing serotonin from the rat basophil leukemia cells when the temperature is raised to 37 degrees C.

Animals↗
PubMed1981

Mobile haptens in liposomes stimulate serotonin release by rat basophil leukemia cells in the presence of specific immunoglobulin E.

A new method for studying the physicochemical determinants of IgE-mediated activation of basophils is described. Rat basophil leukemia cells having IgE receptors were preincubated with monoclonal anti-dinitrophenyl IgE. These cells were then exposed to liposomes containing dinitrophenyl conjugated to phosphatidylethanolamine. The release of serotonin was measured. Using this system it was observed that liposomes containing dinitrophenyl conjugated to phosphatidylethanolamine by aminoethylformamidomethoxy acetyl (but not by caproic acid) were able to trigger the release of serotonin. "Solid" liposomes composed of dipalmitoylphosphatidylcholine and 2 mol % hapten were more potent inducers of serotonin release than "fluid" liposomes composed of dimyristoylphosphatidylcholine and hapten, but the fluid liposomes definitely triggered the cells to release serotonin. The addition of cholesterol to both types of liposomes enhanced their potency as activators and diminished the difference between the two types of phospholipid. This occurred despite the fact that cholesterol renders the solid liposomes fluid. Since it is unlikely that these fluid membranes can provide lateral forces that produce IgE-Fc receptor molecular clustering, we conclude that either receptor clustering is not necessary for basophil triggering, or molecular clustering is driven by molecular forces derived from IgE and components of the basophil cell.

Animals↗
PubMed1979

Fetal liver transplantation in aplastic anemia.

Fetal liver transplantation was attempted in 7 patients with aplastic anemia. 4 of these patients showed a partial response as evidenced by decrease in blood transfusion requirements and increase in the peripheral blood counts and hematopoietic cells in the bone marrow. Bone marrow culture studies revealed evidence of a temporary mixed lymphoid chimerism (cases 1 and 3). While case 1 lived for 16 months, case 3 is surviving at 17 months. None of the patients showed apparent graft-versus-host disease. Increased incidence of infections was noticed. Possible causes for the same are discussed. 3 patients failed to respond. Fetal liver transplant may be of therapeutic value in management of aplastic anemia.

Adolescent↗
PubMed1977

A study of the efficacy of typhoid vaccine in inducing humoral and cell-mediated immune responses in human volunteers.

The nature of protective immunity against typhoid fever in man is not at present well understood. Work on animal models and earlier studies from this laboratory indicate an important protective role for cellular immunity. The present work attempts to study the efficacy of the conventional typhoid vaccine in inducing specific cellular and humoral immune responses. The study on fifty-eight new army recruits and thirty-one civilian volunteers showed adequate humoral responses after vaccination. However, vaccination failed to induce a significant cellular immune response. In addition, a transient suppression of cellular immunity was observed in the immediate post-vaccination period in ten subjects who possessed natural cellular immunity before vaccination. These findings indicate the need for improving the typhoid vaccine so that it will induce cellular immunity as well as a humoral response. It also points to the necessity for obtaining detailed knowledge of the post-vaccination anergy as it could be important in timing public health programmes.

Antibody Formation↗
PubMed1975

Sodium acetate buffer: a diluent of choice in the clot lysis time technique.

Sodium acetate buffer, 0.12 M, pH 7.4 as a diluent in the low temperature technique of dilute clot lysis time, is more effective in accelerating the velocity of lysis than phosphate buffer of similar pH and molarity. A uniform shape of the clot is maintained throughout the digestion in sodium acetate buffer and the end point of lysis is characteristically marked by an abrupt and sharply defined disintegration. Sodium acetate buffer can be employed advantageously in this technique not only to improve the observation but also to shorten the lysis times.

Acetates↗