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Biomedical subjects

R Rajaraman

Publications and source records attributed to R Rajaraman.

At least 19 recordsLinked to original sources
PubMed2001

Effective attraction between like-charged colloids in a two-dimensional plasma.

The existence of attractions between like-charged colloids immersed in ionic solution has been discovered in recent experiments. This phenomenon contradicts the predictions of Derjaguin-Landau-Verwey-Overbeek and indicates a failure of mean-field theory. We study a toy model based on a two-dimensional one-component plasma, which is exactly soluble at one particular coupling constant. We show that colloidal interaction results from a competition between ion-ion repulsion and longer ranged ion-void attraction.

Journal Article↗
PubMed1997

Fibronectin enhances in vitro lipopolysaccharide priming of polymorphonuclear leukocytes.

We investigated the role of humoral factors in lipopolysaccharide (LPS) priming of polymorphonuclear leukocytes (PMN) using cells isolated from adults and from neonates. Plasma from newborn infants had decreased priming activity of adult plasma when mixed with LPS in studies measuring oxidative radical production of PMN after stimulation with a formyl bacterial oligopeptide (fMLP). This marked difference was not caused by LPS binding protein (LBP) because the LBP concentration in newborn and adult plasma were similar (138.4 +/- 12.9 U for adults, and 126.9 +/- 12.1 U for neonates, P = .53). Therefore, we attempted to identify other plasma factors that may contribute to LPS priming of PMN. We identified an LPS priming factor for PMN that is present in plasma, heat stable (56 degrees C for 30 minutes), enhanced by heparin, and concentrated in cold precipitates of plasma. Because these properties resemble those of plasma fibronectin, we assessed the role of fibronectin in LPS priming of PMN. Although fibronectin in phosphate-buffered saline (PBS) had little effect on LPS priming of PMN, fibronectin in combination with other plasma factors appeared to play a role in LPS priming of PMN because (1) removing fibronectin from adult plasma dramatically decreased LPS priming activity from plasma (P < .005), (2) addition of fibronectin to fibronectin-depleted plasma restored its LPS plasma priming activity (P < .05), and (3) neutralizing fibronectin with antibody decreased the LPS priming activity of plasma (60.3 +/- 1.3 v 30.2 +/- 2.2, P < .01). Thus, plasma fibronectin plays a role in LPS priming of PMN in the presence of other factors in plasma.

Adult↗
PubMed1993

Avian integrin alpha v subunit associates with multiple beta subunits and shows tissue-specific variation in its association.

Integrins are heterodimeric cell surface receptors involved in cell adhesion to extracellular matrix proteins and in cell-cell interactions. RGD peptide-specific integrin subunit alpha v and its associated beta subunits were isolated by GRGDSPK-Sepharose affinity chromatography. Using Western blot and immunoprecipitation techniques, the nature of this integrin complexity in the avian system was studied in comparison with that of the human system. As found in human cell systems, in chicken embryo fibroblasts the integrin alpha v subunit is associated with both the 90-kDa beta 3 and the 110-kDa beta 1-like subunits with high specific binding to RGD peptides. Furthermore, immunoprecipitation studies revealed the presence of an unidentified 120-kDa subunit and an 85-kDa beta 5 subunit associated with the alpha v subunit in these cells. No qualitative differences were observed in the beta subunit profile associated with alpha v, as a function of the proliferating nonconfluent or nonproliferating confluent states of the embryonic fibroblast cultures. In adult chicken gizzard, a 110-kDa beta 1-like subunit and a 90-kDa subunit that does not cross-react with anti-H-beta 3 and anti-H-beta 5 are associated with the alpha v subunit. The structure of the novel 120-kDa subunit found in the embryonic fibroblasts and the 90-kDa subunit found in adult chicken gizzard and the ligand specificities of these novel combinations of alpha v are not known at present, but these integrins are RGD specific. It is hypothesized that embryonic fibroblasts, being the primordial proliferating cells, display a wider spectrum of alpha v-associated beta subunits, whose expression may progressively be restricted or highly reduced in favor of one or more beta subunits in subsequent progenies as differentiation progresses.

Amino Acid Sequence↗
PubMed1990

Monoclonal antibodies against Epstein-Barr virus transformed B lymphocytes from a CLL patient.

Immunization of BALB/c mice with EBV-CLL-1 cells, derived from Epstein-Barr virus transformed B lymphocytes from a chronic lymphocytic leukemia (CLL) patient, yielded 2 monoclonal antibodies (IgG1 Kappa and IgG2a Kappa) against a membrane antigen on a subset of normal B lymphocytes and non-Hodgkin's lymphomas. Immunofluorescence revealed strong reactivity of the antibodies with EBV-CLL-1 cells and with most lymphocytes in tonsil follicles, in the intestinal wall, around splenic arterioles and near Hassall's corpuscles in the neonatal thymus as well as with a small proportion of lymphocytes in some large reactive lymph node follicles, weak reactivity with 1/5 of peripheral blood B lymphocytes (PBL), and no reactivity with platelets, granulocytes and non-lymphoid tissues. PBL from 3 CLL patients showed weak staining of only larger cells. Intense fluorescence was observed in several non-Hodgkin's lymphomas of various histological types and in Burkitt's lymphoma lines but not in the 3 T lymphoblastoid and 12 nonlymphoid tumor lines examined. The antibodies precipitated Mr 22,000 and 33,000 bands from surface labeled RAJI or EBV-CLL-1 cells and cross-competed in a binding inhibition assay. The antibodies had approximately 6 million binding sites per EBV-CLL-1 or RAJI cell but were not cytotoxic. This high antigen-density and limited expression in normal cells may permit their use for immunocytological diagnosis and targeting cytotoxic agents and radionuclides against appropriate lymphoma cells.

Animals↗
PubMed1990

Manipulation of macrophage migration inhibition/stimulation responses by adjuvants and interleukins.

C57 B1/6 mice were immunized with bovine serum albumin (BSA) and Freund's complete and incomplete adjuvants in various concentrations. Spleen cells from these animals were subsequently stimulated with concanavalin A (Con A), purified protein derivative or BSA, and lymphokine responses were measured in one-stage migration assays. Con A consistently produced macrophage migration inhibition factor (MIF) responses in nonimmunized animals and those immunized with complete adjuvant. This was switched to migration stimulation factor (MStF) responses by prior immunization with incomplete adjuvant. Immunization with complete adjuvant and with BSA alone was followed by MIF responses to antigenic stimulation whereas incomplete adjuvant promoted MStF responses. The MStF responses to both mitogenic and antigenic stimulation were inhibited by the addition of affinity purified interleukin-1 to the spleen cells. Interleukin-1 also inhibited MStF responses and potentiated MIF responses to Con A stimulation by human mononuclear cells whereas interleukin-2 did not influence these responses.

Animals↗
PubMed1986

The cellular basis for differential lymphokine responses to mitogen stimulation.

Human mononuclear cells from some individuals produce macrophage migration inhibition factor (MIF) when stimulated with Con A while those of others produce migration stimulation factor (MStF). T cells were responsible for these different responses but T4 cells produced MIF and T8 cells produced MStF regardless of the global response which was not explained by the individual T4:T8 ratios. Admixing the T-cell subpopulations in vitro revealed that MIF responses switched to MStF responses between T4:T8 ratios of 75:25 and 50:50 with MStF responders switching at higher ratios than MIF responders. Pulse exposure to supernatants from Con A-stimulated T4-enriched cells significantly reduced migration indices resulting from stimulation of fresh cells, promoting MIF responses regardless of the responder status of the supernatant donor. In contrast, supernatants from T8-enriched cells, when obtained from MStF responders, significantly increased migration indices while there was no effect when the supernatants were obtained from MIF responders. These results suggest that soluble factors from T8 cells are primarily responsible for determining whether an individual mounts a MIF or MStF response to Con A stimulation.

Cell Migration Inhibition↗
PubMed1985

Triazene metabolism. IV. Derivatives of hydroxymethyltriazenes: potential prodrugs for the active metabolites of the anti-tumour triazene, DTIC.

A series of derivatives of the anti-tumour hydroxymethyltriazenes have been investigated for activity in vivo and in vitro. Acetoxymethyltriazenes are active in vivo against the TLX5, P388 and PC6 tumours in mice, and inhibit the growth of TLX5, Np and Li cells in vitro without metabolic activation. The acetoxymethyltriazenes are comparable with the hydroxymethyltriazenes and monomethyltriazenes in their spectrum of activity and thus appear to be prodrugs for these species. On the other hand, a methoxymethyltriazene was found to be active on the TLX5 tumour in vivo, but did not inhibit the growth of Np cells in vitro. This latter observation is consistent with the anticipated chemical stability of the methoxymethyltriazene and the requirement for metabolic O-demethylation to generate an active species. Acetoxymethyltriazenes do not require metabolic intervention and break down chemically in phosphate buffer to the hydroxymethyltriazene, which in turn loses formaldehyde to give the incipient methylating agent, the monomethyltriazene.

Animals↗
PubMed1985

Triazene metabolism. V. Chemical and biological properties of N,N-bis-[(1-aryl-3-methyltriazen-3-yl)-methyl]-methylamines: potential prodrugs for the cytotoxic monomethyltriazenes.

N,N-Bis-[(1-aryl-3-methyltriazen-3-yl)-methyl]-methylamines, 'bistriazenes', have anti-tumour activity against the TLX5 and PC6 mouse tumours and inhibit the growth of tumour cells growing in culture, without metabolic activation. The biological activity of the bistriazene appears to derive from facile hydrolysis to the cytotoxic monomethyltriazene, Ar-N = N-NHMe, and it is suggested that the bistriazene may be a good prodrug from for the 'active' metabolite of the anti-tumour dimethyltriazene, Ar-N-N = N-NME2. A kinetic study of the bistriazene hydrolysis shows that the reaction is retarded by electron-withdrawing substituents in the aryl group. The results can be interpreted by a mechanism in which the bistriazene behaves as an 'animal' (i.e. N-CH2-N) and undergoes anchimerically assisted fragmentation, via an iminium ion intermediate, to the monomethyltriazene.

Animals↗
PubMed1984

Reverse transformation of Chinese hamster ovary cells by methyl xanthines. Structure-function relationships.

Using a number of drugs that increase cellular cAMP levels, alterations in the amount of cell surface fibronectin and other transformation parameters were studied in Chinese hamster ovary (CHO) cells. The drugs include db-cAMP, different methylxanthines (theophylline, aminophylline, methyl isobutyl xanthine (MIX), caffeine and theobromine), papaverine and cholera toxin. Methylxanthines that have a methyl group at the seventh position lack reverse transforming potential; those that lack a methyl group at the seventh position induced reverse transformation in CHO cells, causing an increase in surface fibronectin, cell substratum adhesive strength and anchorage dependence for growth. Further, as methyl xanthines are substituted in other positions different from the seventh position, the more efficient they become in restoring normal phenotypic properties; the later agents also induced low saturation density via a cytostatic state causing accumulation of cells in the S and G2 phases of the cycle in contrast to the G1 arrest of normal cells at low saturation density. db-cAMP and cholera toxin induced cell elongation but like caffeine and theobromine, did not induce surface fibronectin. The non-methylxanthine phosphodiesterase inhibitor papaverine induced neither cell elongation nor surface fibronectin but produced a cytostatic effect similar to aminophylline and MIX. These studies suggest that the reverse transformation properties fall into two groups: (a) Differentiation-related properties including cell morphology, parallel alignment and surface matrix fibronectin, etc.; (b) cell cycle-related properties-low saturation density, cell arrest at G1 phase and anchorage-dependent growth. Phosphodiesterase inhibitors reversibly eliminate indefinite division potential of CHO cells by inducing a cytostatic situation and not by inducing a G1-specific arrest.

Animals↗
PubMed1984

An antigen cross-reacting with anti-laminin sera is found in the submembranous cortical region of various cells in culture.

Laminin is a complex extracellular matrix molecule consisting of one A-subunit (Mr400KD) and 3 B-subunits (Mr220KD) and is found in the basement membrane. Even though it is now apparent that different cell types are synthesizing laminin-like molecules, the role of these molecules in different systems is not well understood. We have characterized laminin and raised specific antiserum in rabbits. The distribution of laminin was studied by indirect immunofluorescence in different cells such as PFHR-9, WI-38, MRC-5, CHO, 3T3, WI38VA132RA, RAW264-7 and Ki3T3. All normal and transformed cells display a high amount of intracellular submembranous network-like component cross-reacting with antilaminin serum (anti-Lm) and not with anti-fibronectin (anti-Fn) serum as seen by immunofluorescence in permeabilized cells. Preabsorption of anti-Lm with increasing amounts of laminin progressively decreased the staining of the submembranous network. Anti-Lm sera from four other laboratories also showed similar staining pattern. The structural and non-secretory nature of this submembranous staining was confirmed by (a) inhibiting protein synthesis in 0.5% serum and 4 micrograms/ml puromycin and (b) by immunoelectron microscopy of permeabilized cells. Immunoprecipitation of 3H-leucine labelled cellular proteins with anti-laminin sera showed proteins of Mr 220-210 KD in SDS-PAGE fluorography. These studies suggest that an antigen(s) crossreacting with anti-Lm sera is localized in the membrane associated cytoskeletal region where spectrin/fodrin family of proteins have been localized.

Animals↗