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Biomedical subjects

M W Verghese

Publications and source records attributed to M W Verghese.

31 records · Page 2Linked to original sources
PubMed1985

Chemoattractant receptor-induced hydrolysis of phosphatidylinositol 4,5-bisphosphate in human polymorphonuclear leukocyte membranes. Requirement for a guanine nucleotide regulatory protein.

Incubation of plasma membranes from human polymorphonuclear leukocytes (PMNs) with [gamma-32P]ATP in the presence of MgCl2 resulted in the formation of 32P-labeled phosphatidic acid (PA), phosphatidylinositol 4-phosphate (PIP), and phosphatidylinositol 4,5-bisphosphate (PIP2). Membranes from PMN specific and azurophil granules synthesized only PIP, suggesting that PIP2 metabolism is confined to the plasma membrane in PMNs. Further incubations of the labeled plasma membranes for 60 s in the presence of 1 mM CaCl2 resulted in the hydrolysis of approximately 40 and 50% of the labeled PIP and PIP2, respectively. In the presence of 2 microM added CaCl2, PIP and PIP2 levels were unchanged by incubation with either the chemoattractant N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe) at 0.1 microM or by 10 microM GTP; however, addition of fMet-Leu-Phe plus GTP together resulted in a 11 and 28% decrease in PIP and PIP2, respectively. These treatments had no effect on PA levels. No additional radiolabeled organic-soluble products were detected after treatment with fMet-Leu-Phe plus GTP. Incubation of intact PMNs, with the Bordetella pertussis toxin (islet-activating protein) eliminated the ability of fMet-Leu-Phe plus GTP to promote PIP2 breakdown in the isolated plasma membranes, but did not inhibit PIP2 degradation in the presence of 1 mM CaCl2. These results provide the first direct evidence that the fMet-Leu-Phe receptor in PMN membranes is coupled to polyphosphoinositide hydrolysis through an islet-activating protein-sensitive guanine nucleotide regulatory protein.

Bacterial Toxins↗
PubMed1985

Potential role for a guanine nucleotide regulatory protein in chemoattractant receptor mediated polyphosphoinositide metabolism, Ca++ mobilization and cellular responses by leukocytes.

Islet activating protein from Bordetella pertussis toxin which ribosylates certain guanine nucleotide regulatory proteins causes a marked reduction of chemoattractant-elicited responses such as chemotaxis, O2 production and cAMP elevations in human polymorphonuclear leukocytes. The toxin appears to exert its effects by preventing the rapid breakdown of phosphatidylinositol 4,5-bisphosphate induced by the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine, thereby inhibiting the increase in intracellular [Ca++] which normally follows chemoattractant stimulation. Responses of leukocytes exposed to Concanavalin A, the Ca++ ionophore A23187, or phorbol myristate acetate were not affected by the toxin. Thus the chemoattractant receptor appears to be coupled to a phosphoinositide specific phospholipase C through a guanine nucleotide regulatory protein. We propose that this complex of receptor-guanine nucleotide regulatory protein-phospholipase C may be applicable to the class of receptors which mobilize intracellular Ca++ by stimulating polyphosphoinositide breakdown.

Bacterial Toxins↗
PubMed1983

Hormonal activation of adenylate cyclase in macrophage membranes is regulated by guanine nucleotides.

Many macrophage functions such as chemotaxis, phagocytosis, enzyme secretion, and cytotoxicity are influenced by intracellular cyclic nucleotide levels, but the regulatory mechanisms involved are poorly defined. We have developed methods that allowed us to study the activation of AC in isolated guinea pig (g.p.) macrophage membranes. AC in these membrane preparations could be stimulated approximately twofold by guanine nucleotides. We could not obtain any hormonal activation of membrane-bound AC in the absence of guanine nucleotides. In the presence of GTP, however, the hormones isoproterenol and PGE1 elicited an additional threefold rise in AC activity, which subsided after approximately 15 min. As little as 10(-8) M concentrations of these two hormones induced significant elevations of AC activity. Replacement of GTP by its nonhydrolyzable analogue Gpp(NH)p resulted in a persistent hormone-independent activation of AC, and addition of hormones enhanced this level of activation. Thus, GTP-ase activity is present in macrophage membrane preparations and serves to regulate AC activation. Hormonal stimulation of AC was receptor mediated, because the effect of the beta-adrenergic agonist isoproterenol, but not PGE1, was inhibited by the beta-adrenergic blocker propranolol. In addition, the potency series of PG corresponded to that observed for stimulation of cAMP production in intact g.p. macrophages, i.e., PGE1 = PGE2 greater than PGA1 greater than PGF2 alpha. AC activation by PG in the membrane preparation was inhibited by an alpha-adrenergic agonist, thus demonstrating one means for down regulating cAMP production in g.p. macrophages. Our studies also showed that certain hormones (e.g., beta-adrenergic agonists, PG) can exert their effect on cAMP production by stimulation of membrane-bound AC, whereas other agents such as lectins or arachidonic acid require additional intracellular components to elevate cAMP levels in macrophages. The mechanism of activation of AC by hormones in g.p. macrophage membranes appears to fit the model of a ternary complex, the components of which include the hormone receptor, AC, and guanine nucleotide regulatory protein, which transmits the signal from the receptor to AC.

Adenylyl Cyclases↗
PubMed1981

Lymphocyte suppressor activity in patients with polyglandular failure.

The Con-A--activated suppressor function of lymphocytes from polyglandular failure (PGF) patients in human mixed lymphocyte culture was compared to a normal population. As a group, PGF patients were found to have decreased suppressor activity: 67% of normal for autologous suppression, 45% of normal for heterologous. However, lymphocytes from most PGF patients have neither an absolute lack of suppressor activity nor an absolute inability to respond to suppression. The marked variability of assayed suppression, depending on the combination of stimulators and responder cells tested, limit the utility of this assay in defining individuals with abnormal suppressor function. One patient's lymphocytes were unique in that although suppression of heterologous cells was normal, suppression of her own cells was defective. Defective suppressor function may be related to the susceptibility of these patients to multiple autoimmune diseases.

Adult↗
PubMed1981

Differential anti-inflammatory effects of LPS in susceptible and resistant mouse strains.

Most mouse strains are highly susceptible to endotoxin (LPS) lethality and are responsive to LPS stimulation in vitro (e.g., B cell mitogenesis, macrophage activation). They are, however, capable of mounting only a small inflammatory response to LPS when it is injected i.p. The present study demonstrates that LPS is in fact a potent, anti-inflammatory agent in all of the five normally LPS susceptible strains tested. LPS was also anti-inflammatory in F1 hybrid mice from susceptible (C3HeB/FeJ) x-resistant (C3H/HeJ) parents. Anti-inflammatory effects of LPS in susceptible strains were achieved by either i.v. or i.p. treatment and were observed toward a variety of phlogistic stimuli including mitogens, C-activating substances, and nonspecific irritants. The most dramatic inhibitory effect of LPS was directed toward the accumulation of inflammatory macrophages. Kinetic studies indicated that the anti-inflammatory effect of a single dose of LPS persisted for at least 72 hr but was maximal when LPS was given simultaneously with the inflammatory stimulus. In contrast to normal mice, two mutant, LPS resistant strains (C3H/HeJ and C57BL10/ScCR) responded to increasing doses of LPS i.p. with a progressively increasing influx of inflammatory cells. In addition, in resistant strains, LPS often enhanced and never depressed the inflammatory response to other phlogistic agents. These studies demonstrate that the genetic regulation of the inflammatory responses to LPS also controls the anti-inflammatory effects of LPS. These responses may be another relevant parameter in determining strain susceptibility to LPS lethality.

Animals↗
PubMed1979

Murine sera cytotoxicity toward human B cells and their effect on human mixed lymphocyte reactions.

Seven murine anti-H-2 and three nonimmune mouse sera were tested for cytotoxicity toward B and T lymphocytes from a panel of human donors. One group of sera, including two anti-H-2.33 sera, exhibited cytotoxicity directed exclusively toward human B but not T cells from all donors. Absorption studies on human lymphoblastoid cell lines (LCLs) of B or T cell origin corroborated these findings. Some nonimmune sera showed similar characteristics, indicating that the observed reactions were not attributable to cross-reactivities between mouse H-2K or D specificities and human antigens coded by the HLA-A, B, or C locus. Another set of mouse sera (anti-H-2.28b and anti-H-2.31) was highly cytotoxic to both B and T cells of some donors but not of others, suggesting that activity in these sera may arise from cross-reactions between mouse and human specifities. A third set of anti-H-2 as well as normal mouse sera showed only background cytotoxicity when tested on human cells. The ability of the B cell cytotoxic mouse sera to block the human mixed lymphocyte culture reaction (MLR) was compared to that of appropriate human alloantisera with exclusive B cell activity or a rabbit serum raised against human B cells. None of the mouse sera resulted in a significant reduction in the human MLR, whereas the human alloantisera as well as the rabbit antiserum caused a significant amount of blocking at several dilutions beyond their highest cytolytic titer.

Animals↗
PubMed1978

Absorption, elution and blocking studies with the complex antiserum ST.

Quantitative absorptions and elutions were performed with the broadly reactive serum ST. The major component of this serum is directed towards the B-locus antigens Bw35, B5, and B18, which comprise the 4c CREG. A second component contains lower titered antibodies which react with members of the 4c CREG, but also appear to detect qualitative and quantitative variations associated with B-locus specificities, B15, B17 and B8. Blocking studies indicate that these antibodies do not bind to the same sites on B8 cells as well-defined anti-B8 sera. These findings are discussed in terms of public specificities at the B-locus or a new specificity at a closely linked locus.

Absorption↗
PubMed1974

Interaction between natural selection for heterozygotes and directional selection.

When directional selection for an additively inherited trait is opposed by natural selection favoring heterozygous genotypes a selection plateau may be reached where genetic variance is present. The amount of response when this plateau is reached is a simple function of the selection response in the first generation and the intensity of natural selection. When selection is practiced in small populations, the sizes of the initial equilibrium gene frequencies are at least as important as the intensity of natural selection in determining the probability of fixing desirable alleles.

Alleles↗
PubMedDate not supplied

Leukocyte activation by chemoattractant receptors: roles of a guanine nucleotide regulatory protein and polyphosphoinositide metabolism.

Chemoattractant receptors on leukocytes are coupled to a guanine nucleotide regulatory (N or G) protein that stimulates a membrane-associated phospholipase C to hydrolyze phosphatidylinositol 4,5-biphosphate. The products of this hydrolysis are inositol 1,4,5-trisphosphate and 1,2-diacylglycerol, which act as second messengers by raising intracellular levels of Ca++ and activating protein kinase C, respectively. These processes promote cellular activation but also initiate reactions that feed back to inhibit the stimulatory pathway.

Animals↗