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Y Harari

Publications and source records attributed to Y Harari.

26 records · Page 2Linked to original sources
PubMed1989

Simulation of parasite-induced gut hypersensitivity: implications for vaccination.

Antigenic challenge of jejunum from rats infected with Trichinella spiralis evokes a biphasic pattern of epithelial Cl- secretion, as measured in vitro by electrophysiological methods. Peaks of secretion occur at approximately 1.5 and approximately 5.0 min post-challenge. Challenge of jejunum from hosts passively immunized with serum containing anti-Trichinella anaphylactic antibody evokes the late phase but not the early phase of Cl- secretion. Since the early phase is mediated by 5-hydroxytryptamine and histamine from mast cells, we hypothesized that the failure to express that phase was due to a decrease in mast cell-derived mediators secondary to a deficiency in mucosal mast cell numbers. The hypothesis was tested by correlating mast cell numbers with patterns of antigen-induced Cl- secretion using several immunization regimes. Rats actively immunized by infection produced anti-Trichinella IgE and had a mucosal mastocytosis. Rats passively sensitized with serum containing anti-Trichinella IgE had normal numbers of mast cells in their mucosa. Inducing mastocytosis in rats, by infecting them with Nippostrongylus brasiliensis prior to passive sensitization with anti-Trichinella serum, primed for the expression of a biphasic Cl- secretory response upon subsequent challenge with Trichinella antigen. Rats actively sensitized by injection with Trichinella antigen elicited an IgE response without mastocytosis and expressed only the late phase of antigen-induced Cl- secretion. Results (i) support our hypothesis, (ii) emphasize the importance of the cellular state of the mucosa in the functional expression of local anaphylaxis; and (iii) provide a physiological explanation for the general failure of vaccination and passive sensitization to induce functional immunity equivalent to that induced by natural infection.

Anaphylaxis↗
PubMed1988

Evaluation of a possible functional relationship between chemical structure of intestinal brush border and immunity to Trichinella spiralis in the rat.

Primary exposure to Trichinella spiralis in the rat, while immunizing against reinfection, induces changes in the carbohydrate structure of intestinal brush border membranes. Immunity is expressed in heightened resistance to mucosal invasion by L1 larvae, and the change in structure is evident in reduced membrane binding of the lectin, wheat germ agglutinin. The possibility that altered membrane composition is a requisite for expression of immunity was hypothesized and this was evaluated by correlating the maximum, specific binding of wheat germ agglutinin by isolated brush border membranes with (1) the expression of immunity acquired passively through serum transfer, and (2) the loss of immunity acquired from serial infections terminated in the intestinal phase. The hypothesis was further evaluated by determining whether the change in membrane structure represents a stimulus-specific response. We observed that (1) passively acquired immunity was not associated with a reduction in lectin binding and (2) short-term exposure to the intestinal stages of T. spiralis led to a reduction in lectin binding that was detectable at a time when rats were incapable of resisting reinfection. The change in lectin binding associated with trichinosis also accompanied infection with Nippostrongylus brasiliensis. Results uniformly support the conclusion that immunity to T. spiralis is independent of brush border membrane changes reflected in reduced binding of wheat germ agglutinin.

Animals↗
PubMed1987

Anaphylaxis-mediated epithelial Cl- secretion and parasite rejection in rat intestine.

Immunologically mediated expulsion of Trichinella spiralis infective larvae in the rat was used as a model to test the hypothesis that intestinal anaphylaxis induced by parasite antigen causes ion transport alterations in small intestinal epithelium, and that the small intestinal epithelium, by altering its physiologic state in response to mast cell-derived mediators, functions as an effector tissue in the expulsion process. Experimental results demonstrated that the rapid rejection response and antigen-inducible changes in net intestinal ion transport acquired through active immunization were transferable with serum containing a high titer of anti-trichinella homocytotropic antibody, as measured by the PCA test. Neither response was expressed in nonimmune hosts nor in recipients of serum in which the PCA-detectable antibody was reduced by heat treatment. Net ion transport by jejunal epithelium of both actively and passively immunized rats was measured in Ussing chambers by using the electrical correlate, short circuit current (Isc). Involvement of chloride secretion in antigen-induced alterations in Isc was deduced from the use of chemical agents that effectively and specifically blocked the antigen-induced Cl- secretory response. The results implicate anaphylaxis in both rapid worm rejection and altered epithelial ion transport.

Anaphylaxis↗
PubMed1987

Mediators of anaphylaxis-induced ion transport changes in small intestine.

Net ion transport by jejunum of rats immunized against Trichinella spiralis on challenge with parasite-derived antigen was measured in Ussing chambers as a rapidly expressed, biphasic rise and fall (phase I and II) in short-circuit current (delta Isc). This delta Isc is triggered by mucosal anaphylaxis. Our objective is to identify mast cell-derived substances that mediate the epithelial response. Antigenic challenge of sensitized jejunum caused the release of 5-hydroxytryptamine (5-HT), histamine, and prostaglandin E2 (PGE2). The antigen-induced phase I response was mimicked by exogenous 5-HT or histamine and blocked by pretreatment of tissue with 5-HT and histamine H1-antagonists; the phase II response was mimicked by exogenous PGE2 and blocked by an inhibitor of prostaglandin synthesis. Atropine and tetrodotoxin significantly blunted the phase I response as well as the delta Isc caused by exogenous 5-HT or histamine while only slightly reducing the phase II response and not affecting the delta Isc induced by PGE2. Results support the conclusion that 5-HT, histamine, and PGE2 mediate the antigen-induced change in Isc through direct and neurally mediated stimulation of jejunal epithelium.

Anaphylaxis↗
PubMed1985

Phosphatidylethanolamine methylation in intestinal brush border membranes from rats resistant to Trichinella spiralis.

Methylation of phospholipids is proposed as a mechanism to explain changes in properties of intestinal brush border membrane that coincide with development of immunity to the intraepithelial parasite, Trichinella spiralis. Methylation was measured by the incorporation of the [3H]methyl group from S-adenosyl-L-[3H]methyl methionine into phospholipids. At least two enzymatic components were detected that converted phosphatidylethanolamine to phosphatidylcholine. The first, designated methyltransferase I, catalyzed the formation of phosphatidylmonomethylethanolamine from phosphatidylethanolamine and had a low Km for S-adenosyl-L-methyl-methionine (5 microM). The second, designated methyltransferase II, which catalyzed the methylation of phosphatidylmonomethylethanolamine to phosphatidyldimethylethanolamine and phosphatidyldimethylethanolamine to phosphatidylcholine, had a high Km for S-adenosyl-L-methyl methionine (167 microM). Both enzymes had two pH optima, were most active at 37 degrees C and were Mg2+ dependent. A decrease in methylation activity was present in brush border membranes from rats immunized against T. spiralis. Although the synthesis of phosphatidylcholine was not significantly altered there was a substantial decrease in the formation of phosphatidylmonomethylethanolamine and phosphatidyldimethylethanolamine as compared with nonimmunized rats. Since phospholipid composition influences membrane fluidity and cell function, it is proposed that altered methylation activity may influence the characteristics of brush border membrane in the immune host.

Animals↗
PubMed1983

Sialic acid deficiency in lectin-resistant intestinal brush border membranes from rats following the intestinal phase of trichinellosis.

Maximal binding (Bmax) of the lectin, wheat germ agglutinin, by small intestinal brush border membrane is significantly reduced in rats infected with Trichinella spiralis. Wheat germ agglutinin specificity is for N-acetylglucosamine and sialic acid. Whereas total hexosamine and N-acetylglucosaminidase-labile N-acetylglucosamine were comparable in membranes from uninfected as compared with infected rats, the total sialic acid content and neuraminidase-released sialic acid were significantly higher in BBM from uninfected hosts. N-Acetylglucosaminidase treatment of membranes reduced Bmax for wheat germ agglutinin in both hosts. Neuraminidase treatment reduced Bmax in uninfected hosts, but tended to increase it in infected rats. Membranes from uninfected rats incorporated more N-acetylglucosamine from UDP-N-[14C]acetylglucosamine into oligosaccharide-lipid than did membranes from infected hosts. However, lipid and protein fractions were labeled at the same rate in both sets of membranes. Sialic acid was incorporated into protein at a slightly faster rate in brush border membrane from uninfected rats, indicative of a higher level of sialotransferase activity. These results suggest that the reduction in Bmax for wheat germ agglutinin in gut epithelial cell membranes from infected rats is related to a reduced level of sialic acid available for lectin binding as well as specific interactions between N-acetylglucosamine and sialic acid.

Acetylglucosamine↗
PubMed1982

Intestinal epithelial membrane changes in rats immune to Trichinella spiralis.

Establishment of Trichinella spiralis infective larvae is blocked to a large degree in the immune rat as compared with the nonimmune host. The rapidity with which this response occurs indicates that most worms are either prevented from penetrating the intestinal epithelium or are rejected immediately after cell entry. It is proposed that interference with larval infectivity is due to alterations in the epithelial cell apical or brush border membrane. Alterations may result from prior infection or may reflect an acute change induced by challenge infection. In either case the establishment of normal populations of larvae in the mucosa is disturbed. Lectin binding capacity of brush border membranes was used to assess possible membrane alterations. This parameter in uninfected (control) rats was compared with that in infected rats, which acquire resistance to subsequent challenge, and in infected rats immediately after a challenge inoculum. Enriched brush border membrane preparations were characterized for their binding of wheat germ agglutinin, which attaches specifically to the carbohydrate, N-acetylglucosamine. Maximum specific binding of 125I-labeled wheat germ agglutinin occurred within 20 min. The spontaneous rate of dissociation was negligible for 90 min. Highest specific binding resulted at 24 degrees C, pH 6.0 and with 75 micrograms brush border membrane protein per assay tube. Results suggested the existence of multiple binding sites. 1 mg of membrane protein from uninfected rats and rats immunized by primary infection maximally bound 9.8 X 10(10) and 4.3 X 10(10) molecules of wheat germ agglutinin, respectively. Binding for the 'immune' brush border membrane, as compared with the 'uninfected' brush border membrane was reduced during the first 3 weeks of infection and remained low for at least 3 months. No further reduction in binding was observed for brush border membrane isolated within minutes after a secondary infection. These results reveal the induction by a primary infection of changes in brush border membrane structure and the persistence of these changes in the immune host. In view of the rapid turnover time of epithelial tissue the mechanism by which this change is perpetuated speculatively involves immune elements in the lamina propria.

Animals↗