Epstein-Barr virus infection of Langerhans cell precursors as a mechanism of oral epithelial entry, persistence, and reactivation.

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus associated with many malignant and nonmalignant human diseases. Life-long latent EBV persistence occurs in blood-borne B lymphocytes, while EBV intermittently productively replicates in mucosal epithelia. Although several models have previously been proposed, the mechanism of EBV transition between these two reservoirs of infection has not been determined. In this study, we present the first evidence demonstrating that EBV latently infects a unique subset of blood-borne mononuclear cells that are direct precursors to Langerhans cells and that EBV both latently and productively infects oral epithelium-resident cells that are likely Langerhans cells. These data form the basis of a proposed new model of EBV transition from blood to oral epithelium in which EBV-infected Langerhans cell precursors serve to transport EBV to the oral epithelium as they migrate and differentiate into oral Langerhans cells. This new model contributes fresh insight into the natural history of EBV infection and the pathogenesis of EBV-associated epithelial disease.

THE ROLE OF MUCOSAL EPITHELIAL CELLS IN HIV-1 INFECTION

The predominant route of human immunodeficiency virus type 1 (HIV-1) transmission is infection across the vaginal mucosa. Epithelial cells, which form the primary barrier of protection against pathogens, are the first cell type at these mucosal tissues to encounter the virus but their role in HIV infection has not been clearly elucidated. Although mucosal epithelial cells express only low levels of the receptors required for successful HIV infection, productive infection does occur at these sites. The present work provides evidence to show that HIV exposure, without the need for productive infection, induces human cervical epithelial cells to produce Thymic Stromal Lymphopoietin (TSLP), an IL7-like cytokine, which potently activated human myeloid dendritic cells (mDC) to cause the homeostatic proliferation of autologous CD4+ T cells that serve as targets for HIV infection. Rhesus macaques inoculated with simian immunodeficiency virus (SIV) or with the simian-human immunodeficiency virus (SHIV) by the vaginal, oral or rectal route exhibited dramatic increases in: TSLP expression, DC and CD4+ T cell numbers, and viral replication, in the vaginal, oral, and rectal tissues, respectively within the first 2 weeks after virus exposure. Evidence obtained showed that HIV-mediated TSLP production by cervical cells is dependent upon the expression of the cell surface salivary agglutinin (SAG) protein gp340. Epithelial cells expressing gp340 exhibited HIV endocytosis and TSLP expression and genetic knockdown of gp340 or use of a gp340-blocking antibody inhibited TSLP expression by HIV. On the other hand, gp340-null epithelial cells failed to endocytose HIV and produce TSLP, but transfection of gp340 resulted in HIV-induced TSLP expression. Finally, HIV-induced TSLP expression was found to be mediated by TLR7/8 signaling and NF-kB activity because silencing these pathways or use of specific inhibitors abrogated TSLP expression in gp340-postive but not in gp340-null epithelial cells. Overall these studies identify TSLP as a key player in the acute phase of HIV-1 infection in permitting HIV to successfully maneuver the hostile vaginal mucosal microenvironment by creating a conducive environment for sustaining the small amount of virus that initially crosses the mucosal barrier allowing it to successfully cause infection and spread to distal compartments of the body

LOSS OF GPRC5A ENHANCES SURVIVAL IN NORMAL AND MALIGNANT LUNG EPITHELIAL CELLS BY ELICITING PERSISTENT STAT3 ACTIVATION INDUCED BY AUTOCRINE LIF

Signal transduction and activator of transcription 3 (Stat3) is activated by cytokines and growth factors in many cancers. Persistent activation of Stat3 plays important role in cell growth, survival, and transformation through regulating its targeted genes. Previously, we found that mice with a deletion of the G protein-coupled receptor, family C, group 5, member a (Gprc5a) gene develop lung tumors indicating that Gprc5a is a tumor suppressor. In the present study, we examined he mechanism of Gprc5a-mediated tumor suppression. We found that epithelial cells from Gprc5a knockout mouse lung (Gprc5a-/- cells) survive better in vitro in medium deprived of exogenous growth factors and form more colonies in semi-solid medium than their counterparts from wildtype mice (Gprc5a+/+ cells). The phosphorylation of tyrosine 705 on Stat3 and the expression of Stat3-regulated anti-apoptotic genes Bcl-XL, Cryab, Hapa1a, and Mcl1 were higher in the Gprc5a-/- than in Gprc5a+/+ cells. In addition, their responses to Lif were different; Stat3 activation was persistent by Lif treatment in the Gprc5a-/- cells, but was transient in the Gprc5a+/+ cells. The persistent activation of Stat3 by Lif in Gprc5a-/- cells is due to a decreased level of Socs3 protein, a negative inhibitor of the Lif-Stat3 signaling. Restoration of Socs3 inhibited the persistent Stat3 activation in Gprc5a-/- cells. Lung adenocarcinoma cells isolated from Gprc5a-/- mice also exhibited autocrine Lif-mediated Stat3 activation. Treatment of Gprc5a-/- cells isolated from normal and tumor tissue with AG490, a Stat3 signaling inhibitor, or with dominant negative Stat3(Y705F) increased starvation-induced apoptosis and inhibited anchorage-independent growth. These results suggest that persistent Stat3 activation increased the survival and transformation of Gprc5a-/- lung cells. Thus, the tumor suppressive effects of Gprc5a are mediated, at least in part, by inhibition of Stat3 signaling through regulating the stability of the Socs3 protein.

NHERF1 – New Modifier of Colorectal Cancer Progression

Colorectal cancer (CRC) develops from multiple progressive modifications of normal intestinal epithelium into adenocarcinoma. Loss of cell polarity has been implicated as an early event in this process, but the molecular players involved are not well known. NHERF1 (Na+/H+ Exchanger Regulatory Factor 1) is an adaptor protein with apical membrane localization in polarized epithelia. In this study, we tested our hypothesis that NHERF1 plays a role in CRC. We examined surgical CRC resection specimens for changes in NHERF1 expression, and modeled these changes in two- and three-dimensional (2D and 3D) Caco-2 CRC cell systems. NHERF1 had significant alterations from normal to adenoma and carcinoma transitions (2=38.5, d.f.=4, P<0.001), displaying apical membrane localization in normal tissue but loss of expression in adenoma and ectopic overexpression in carcinoma. In Caco-2 cell models, NHERF1 depletion induced epithelial-mesenchymal-transition in 2D cell monolayers and disruption of apical-basal polarity in 3D cyst system. The mesenchymal phenotype of NHERF1-depleted cells was fully restored by re-expression of NHERF1 at the apical membrane. Cytoplasmic and nuclear NHERF1 re-expression not only failed to restore the epithelial phenotype but led to more aggressive phenotypes. Our findings suggest that membrane NHERF1 is an important regulator of epithelial morphogenesis, and that changes in NHERF1 expression correlate with CRC progression. NHERF1 loss and ectopic expression that induce massive disruption of epithelial cell polarity may, thereby, mark important steps in CRC development.

Persistent Productive Epstein‐Barr Virus Replication in Normal Epithelial Cells In Vivo

Productive Epstein‐Barr virus (EBV) replication characterizes hairy leukoplakia, an oral epithelial lesion typically occurring in individuals infected with human immunodeficiency virus (HIV). Serial tongue biopsy specimens were obtained from HIV‐infected subjects before, during, and after valacyclovir treatment. EBV replication was detected by Southern hybridization to linear terminal EBV genome fragments, reverse‐transcriptase polymerase chain reaction amplification of EBV replicative gene transcripts, immunohistochemical detection of EBV replicative protein, and in situ hybridization to EBV DNA. EBV replication was detected in both hairy leukoplakia and normal tongue tissues. Valacyclovir treatment completely abrogated EBV replication in vivo, resulting in resolution of hairy leukoplakia when it was present. EBV replication returned in normal tongue epithelial cells after valacyclovir treatment. These data suggest that normal oral epithelium supports persistent EBV infection in individuals infected with HIV and that productive EBV replication is necessary but not sufficient for the pathogenesis of oral hairy leukoplakia.

CELL POLARITY REGULATES ORGAN GROWTH THROUGH THE HIPPO PATHWAY

Defects in apical-basal cell polarity and abnormal expression of cell polarity determinants are linked to human cancer. Loss of polarity is highly correlated with malignancy. In Drosophila, perturbation of apical-basal polarity, including overexpressing the apical determinant Crumbs, can lead to uncontrolled tissue growth. Cells mutant for the basolateral determinant scribble overproliferate and can form neoplastic tumors. Interestingly, scribble mutant clones that arise in wild-type tissues are eliminated and therefore do not manifest their tumorigenic potential. However, the mechanisms by which cell polarity coordinates with growth control pathways in developing organs to achieve appropriate organ size remain obscure. To investigate the function of apical determinants in growth regulation, I investigated the mechanism by which the apical determinant Crumbs affects growth in Drosophila imaginal discs. I found that crumbs gain and loss of function cause overgrowth and induction of Hippo target genes. In addition, Crumbs is required for the proper localization of Expanded, an upstream component of the Hippo pathway. Furthermore, we uncoupled the cell polarity and growth control function of Crb through structure-functional analysis. Taken together, our data identify a role of Crb in growth regulation specifically through modulation of the Hippo pathway. To further explore the role of polarity in growth control, I investigated how cells mutant for basolateral determinants are eliminated by using patches of cells mutant for scribble (scribble mutant clones) as a model system. We found that competitive cell-cell interactions eliminate tumorigenic scribble cells by modulation of the Hippo pathway. The regulation of Hippo signaling is required and sufficient to restrain the tumorous growth of scribble mutant cells. Artificially increasing the relative fitness of scribble mutant cells unleashes their tumorigenic potential. Therefore, we have identified a novel tumor-suppression mechanism that depends on signaling between normal and tumorigenic cells. These data identify evasion of cell competition as a critical step toward malignancy and illustrate a role for wild-type tissue in eliminating abnormal cells and preventing the formation of tumors.

Sp1 up-regulates cAMP-response-element-binding protein expression during retinoic acid-induced mucous differentiation of normal human bronchial epithelial cells.

CREB [CRE (cAMP-response element)-binding protein] is an important transcription factor that is differentially regulated in cells of various types. We recently reported that RA (retinoic acid) rapidly activates CREB without using RARs (RA receptors) or RXRs (retinoid X receptors) in NHTBE cells (normal human tracheobronchial epithelial cells). However, little is known about the role of RA in the physiological regulation of CREB expression in the early mucous differentiation of NHTBE cells. In the present study, we report that RA up-regulates CREB gene expression and that, using 5'-serial deletion promoter analysis and mutagenesis analyses, two Sp1 (specificity protein 1)-binding sites located at nt -217 and -150, which flank the transcription initiation site, are essential for RA induction of CREB gene transcription. Furthermore, we found that CREs located at nt -119 and -98 contributed to basal promoter activity. Interestingly, RA also up-regulated Sp1 in a time- and dose-dependent manner. Knockdown of endogenous Sp1 using siRNA (small interfering RNA) decreased RA-induced CREB gene expression. However, the converse was not true: knockdown of CREB using CREB siRNA did not affect RA-induced Sp1 gene expression. We conclude that RA up-regulates CREB gene expression during the early stage of NHTBE cell differentiation and that RA-inducible Sp1 plays a major role in up-regulating human CREB gene expression. This result implies that co-operation of these two transcription factors plays a crucial role in mediating early events of normal mucous cell differentiation of bronchial epithelial cells.

Transplantation of human embryonic stem cell-derived alveolar epithelial type II cells abrogates acute lung injury in mice.

Respiratory diseases are a major cause of mortality and morbidity worldwide. Current treatments offer no prospect of cure or disease reversal. Transplantation of pulmonary progenitor cells derived from human embryonic stem cells (hESCs) may provide a novel approach to regenerate endogenous lung cells destroyed by injury and disease. Here, we examine the therapeutic potential of alveolar type II epithelial cells derived from hESCs (hES-ATIICs) in a mouse model of acute lung injury. When transplanted into lungs of mice subjected to bleomycin (BLM)-induced acute lung injury, hES-ATIICs behaved as normal primary ATIICs, differentiating into cells expressing phenotypic markers of alveolar type I epithelial cells. Without experiencing tumorigenic side effects, lung injury was abrogated in mice transplanted with hES-ATIICs, demonstrated by recovery of body weight and arterial blood oxygen saturation, decreased collagen deposition, and increased survival. Therefore, transplantation of hES-ATIICs shows promise as an effective therapeutic to treat acute lung injury.

A pure population of lung alveolar epithelial type II cells derived from human embryonic stem cells.

Alveolar epithelial type II (ATII) cells are small, cuboidal cells that constitute approximately 60% of the pulmonary alveolar epithelium. These cells are crucial for repair of the injured alveolus by differentiating into alveolar epithelial type I cells. ATII cells derived from human ES (hES) cells are a promising source of cells that could be used therapeutically to treat distal lung diseases. We have developed a reliable transfection and culture procedure, which facilitates, via genetic selection, the differentiation of hES cells into an essentially pure (>99%) population of ATII cells (hES-ATII). Purity, as well as biological features and morphological characteristics of normal ATII cells, was demonstrated for the hES-ATII cells, including lamellar body formation, expression of surfactant proteins A, B, and C, alpha-1-antitrypsin, and the cystic fibrosis transmembrane conductance receptor, as well as the synthesis and secretion of complement proteins C3 and C5. Collectively, these data document the successful generation of a pure population of ATII cells derived from hES cells, providing a practical source of ATII cells to explore in disease models their potential in the regeneration and repair of the injured alveolus and in the therapeutic treatment of genetic diseases affecting the lung.

Coordinated changes in mRNA turnover, translation, and RNA processing bodies in bronchial epithelial cells following inflammatory stimulation.

Bronchial epithelial cells play a pivotal role in airway inflammation, but little is known about posttranscriptional regulation of mediator gene expression during the inflammatory response in these cells. Here, we show that activation of human bronchial epithelial BEAS-2B cells by proinflammatory cytokines interleukin-4 (IL-4) and tumor necrosis factor alpha (TNF-alpha) leads to an increase in the mRNA stability of the key chemokines monocyte chemotactic protein 1 and IL-8, an elevation of the global translation rate, an increase in the levels of several proteins critical for translation, and a reduction of microRNA-mediated translational repression. Moreover, using the BEAS-2B cell system and a mouse model, we found that RNA processing bodies (P bodies), cytoplasmic domains linked to storage and/or degradation of translationally silenced mRNAs, are significantly reduced in activated bronchial epithelial cells, suggesting a physiological role for P bodies in airway inflammation. Our study reveals an orchestrated change among posttranscriptional mechanisms, which help sustain high levels of inflammatory mediator production in bronchial epithelium during the pathogenesis of inflammatory airway diseases.

Aldosterone-induced Sgk1 relieves Dot1a-Af9-mediated transcriptional repression of epithelial Na+ channel alpha.

Aldosterone plays a major role in the regulation of salt balance and the pathophysiology of cardiovascular and renal diseases. Many aldosterone-regulated genes--including that encoding the epithelial Na+ channel (ENaC), a key arbiter of Na+ transport in the kidney and other epithelia--have been identified, but the mechanisms by which the hormone modifies chromatin structure and thus transcription remain unknown. We previously described the basal repression of ENaCalpha by a complex containing the histone H3 Lys79 methyltransferase disruptor of telomeric silencing alternative splice variant a (Dot1a) and the putative transcription factor ALL1-fused gene from chromosome 9 (Af9) as well as the release of this repression by aldosterone treatment. Here we provide evidence from renal collecting duct cells and serum- and glucocorticoid-induced kinase-1 (Sgk1) WT and knockout mice that Sgk1 phosphorylated Af9, thereby impairing the Dot1a-Af9 interaction and leading to targeted histone H3 Lys79 hypomethylation at the ENaCalpha promoter and derepression of ENaCalpha transcription. Thus, Af9 is a physiologic target of Sgk1, and Sgk1 negatively regulates the Dot1a-Af9 repressor complex that controls transcription of ENaCalpha and likely other aldosterone-induced genes.

Enforced expression of Tbx1 in fetal thymic epithelial cells antagonizes thymus organogenesis

Enforced expression of Tbx1 in fetal thymic epithelial cells antagonizes thymus organogenesis Kim T. Cardenas The thymus and parathyroid glands originate from organ-specific domains of 3rd pharyngeal pouch (PP) endoderm. At embryonic day 11.5 (E11.5), the ventral thymus and dorsal parathyroid domains can be identified by Foxn1 and Gcm2 expression respectively. Neural crest cells, (NCCs) play a role in regulating patterning of 3rd PP endoderm. In addition, pharyngeal endoderm influences fate determination via secretion of Sonic hedgehog (Shh), a morphogen required for Gcm2 expression and generation of the parathyroid domain. Gcm2 is a downstream target of the transcription factor Tbx1, which in turn is positively regulated by Shh. Although initially expressed throughout pharyngeal pouch endoderm, Tbx1 expression is excluded from the thymus-specific domain of the 3rd PP by E10.5, but persists in the parathyroid domain. Based on these observations, we hypothesized that Tbx1 expression is non-permissive for thymus fate specification and that enforced expression of Tbx1 in the fetal thymus would impair thymus development. To test this hypothesis, we generated knock-in mice containing a Cre-inducible allele that allows for tissue-specific Tbx1 expression. Expression of the R26iTbx1 allele in fetal and adult thymus using Foxn1Cre resulted in severe thymus hypoplasia throughout ontogeny that persisted in the adult. Thymic epithelial cell (TEC) development was impaired as determined by immunohistochemical and FACS analysis of various differentiation markers. The relative level of Foxn1 expression in fetal TECs was significantly reduced. TECs in R26iTbx1/+ thymi assumed an almost universal expression of Plet-1, a marker associated with a TEC stem/progenitor cell fate. In addition, embryonic R26iTbx1/+ mice develop a perithymic mesechymal capsule that appears expanded compared to control littermates. Interestingly, thymi from neonatal and adult R26iTbx1/+ but not R26+/+ mice were encased in adipose tissue. This thymic phenotype also correlated with a decrease in thymocyte cellularity and aberrant thymocyte differentiation. The results to date support the conclusion that enforced expression of Tbx1 in TECs antagonizes their differentiation and prevents normal organogenesis via both direct and indirect effects.

The characterization of an epithelial chloride channel and purification of a channel component

A membrane fraction (M$\sb{\rm PS}$), enriched in Cl$\sp-$ channels, has been isolated from bovine tracheal epithelia and renal cortex homogenates by hydrophobic chromatography. The tracheal fraction shows a 37 fold enrichment of Cl$\sp-$ channels over crude tracheal homogenates by net Cl$\sp-$ measurements in membrane vesicles. Alkaline phosphatase and (Na$\sp+$ + K$\sp+$)-ATPase are not found in these membranes, suggesting that they are not apical or basolateral plasma membranes. The M$\sb{\rm PS}$ fraction exhibits a protein profile unlike that of other membrane fractions with major proteins of 200 kDa and 42 kDa, proteins of 30 to 35 kDa, and lesser amounts of other proteins. Reconstitution of M$\sb{\rm PS}$ fractions from both trachea and kidney into planar lipid bilayers demonstrates the presence of a single type of anion channel. The current-voltage relationship of this channel is linear with a slope conductance of 84 pS in symmetrical 400 mM KCl, and is identical to that of the predominant anion channel observed in tracheal apical membranes under similar conditions (Valdivia, Dubinsky, and Coronado. Science, 1988). In addition, the voltage dependence, selectivity sequence of Cl$\sp- >$ Br$\sp- \ge$ I$\sp-$, and inhibition by low concentrations of the Cl$\sp-$ channel blocker, DIDS, correspond to those of the predominant apical membrane channel. Thus, although the M$\sb{\rm PS}$ fraction appears to be of subcellular origin, it may be functionally related to an apical membrane Cl$\sp-$ permeability. When renal M$\sb{\rm PS}$ membranes were treated with the detergent octyl-glucoside (OG, 2%) and centrifuged, the supernatant, sM$\sb{\rm PS}$, showed a 2 to 7-fold enrichment in specific Cl$\sp-$ flux activity compared with the detergent treated M$\sb{\rm PS}$. These solubilized proteins were then size fractionated on a Superose 12 HPLC gel filtration column, followed by fractionation on a Mono Q HPLC anion exchange column. Fractions that eluted in high salt consistently exhibited significant Cl$\sp-$ flux activity. These fractions had protein profiles consisting of a major band at 34 kDa, a band at 66 kDa, and variable faint bands. Fractions eluting in lower salt had protein profiles consisting of a single band at 34 kDa, and often had little or no Cl$\sp-$ flux activity. However, co-reconstitution of the low salt, solely 34 kDa protein-containing Mono Q fractions with sM$\sb{\rm PS}$ resulted in an enhancement of flux activity compared to that of sM$\sb{\rm PS}$ reconstituted alone. Flux assays of active Mono Q fractions showed that the channel retained its DIDS sensitivity. Applying sM$\sb{\rm PS}$ to a DIDS-affinity column and eluting with salt resulted in fractions with protein profiles again consisting of at least one major band at 34 kDa, a band at 66 kDa, and variable faint bands. Co-reconstitution with sM$\sb{\rm PS}$ again resulted in an enhancement of activity. Thus, the 34 kDa protein appears to be a component of the M$\sb{\rm PS}$ Cl$\sp-$ channel. ^

Expression and hormonal regulation of Muc-1 at the apical surface of mouse uterine epithelial cells and its role in modulating embryo implantation

Previous studies from our lab have established that large molecular weight mucin glycoproteins are major apically-disposed components of mouse uterine epithelial cells in vitro (Valdizan et al., (1992) J. Cell. Physiol. 151:451-465). The present studies demonstrate that Muc-1 represents one of the apically-disposed mucin glycoproteins of mouse uterine epithelia, and that Muc-1 protein and mRNA expression are regulated in the peri-implantation stage mouse uterus by ovarian steroids. Muc-1 expression is high in the proestrous and estrous stages, and decreases during diestrous. Both Muc-1 protein and mRNA levels decline to barely detectable levels by day 4 of pregnancy, i.e., prior to the time of blastocyst attachment. In contrast, Muc-1 expression in the cervix and vagina is maintained during this same period. Delayed implantation was established in pregnant mice by ovariectomy and maintained by administration of exogenous progesterone. Initiation of implantation was triggered by coinjection of progesterone maintained mice with a nidatory dose of 17$\beta$-estradiol. Muc-1 levels in the uterine epithelia of progesterone maintained mice declined to similar low levels as observed on day 4 of normal pregnancy. Coinjection of estradiol did not alter Muc-1 expression suggesting that down-regulation of Muc-1 is a progesterone dominated event. This was confirmed in ovariectomized, non-pregnant mice which displayed stimulation of Muc-1 expression following 6 hr of estradiol injection. Estradiol stimulated Muc-1 expression was inhibited by the pure antiestrogen, ICI 164,384. While progesterone alone had no effect on Muc-1 expression, it antagonized estradiol action in this regard. Injection of pregnant mice with the antiprogestin, RU 486, a known implantation inhibitor, on day 3 of pregnancy restored high level expression of Muc-1 mRNA on day 4, indicating that down-regulation of Muc-1 is progesterone receptor-mediated. Muc-1 appears to function as an anti-adhesive molecule at the apical cell surface of mouse uterine epithelial cells. Treatment of polarized cultures of mouse uterine epithelial cells with O-sialoglycoprotein endopeptidase reduced mucin expression in vitro, by about 50%, and converted polarized uterine epithelia to a functionally receptive state. Similarly, ablation of Muc-1 in Muc-1 null mice resulted in polarized uterine epithelia that were functionally receptive as compared to their wild-type counterparts in vitro. Collectively, these data indicate that Muc-1 and other mucins function as anti-adhesive molecules and that reduction or removal of these molecules is a prerequisite for the generation of a receptive uterine state. ^

ANAPHYLACTICALLY - MEDIATED EPITHELIAL CHLORINE ION SECRETORY RESPONSE INISOLATED JEJUNUM OF PARASITIZED GUINEA PIGS (TRICHINELLA SPIRALIS)

Electrophysiological studies were conducted to test the hypothesis that alterations in intestinal epithelial function are associated with immunological responses directed against the enteric parasite, Trichinella spirals. Trichinella antigens were used to challenge sensitized jejunum from infected guinea pigs while monitoring ion transport properties of the tissue in an Ussing-type chamber. The addition of antigen caused increases in transepithelial PD and I(,sc) that were rapidly induced, peaked at 1.5 to 2 min after antigen-challenge, and lasted 10 to 20 min thereafter. The increase in I(,sc) ((DELTA)I(,sc)) varied in a dose-dependent manner until a maximal increase of 40 (mu)A/cm('2) was obtained by the addition of 13 (mu)g of antigenic protein per ml of serosal fluid in the Ussing chamber. Trichinella antigen did not elicit alterations in either PD or I(,sc) of nonimmune tissue. Jejunal tissue from guinea pigs immunized with ovalbumin according to a protocol that stimulated homocytotropic antibody production responded electrically to challenge with ovalbumin but not trichinella antigen. Jejunal tissue which was passively sensitized with immune serum having a passive cutaneous anaphylaxis (PCA) titer of 32 for both IgE and IgG(,1) anti-trichinella anti-bodies responded electrically after exposure to trichinella antigen. Heat treatment of immune serum abolished the anti-trichinella IgE titer as determined by the PCA test but did not decrease either the electrical response of passively sensitized tissue to antigen or the anaphylactically mediated intestinal smooth muscle contractile response to antigen in the classical Schultz-Dale assay. These results strongly support the hypothesis that immunological responses directed against Trichinella Spiralis alter intestinal epithelial function and suggest that immediate hypersensitivity is the immunological basis of the response.^ Additional studies were performed to test the hypothesis that histamine and prostaglandins that are released from mucosal mast cells during IgE or IgG(,1) - antigen stimulated degranulation mediate electrophysiological changes in the intestinal epithelium that are reflective of Cl('-) secretion and mediated intracellularly by cAMP. Pharmacological and biochemical studies were performed to determine the physiological messengers and ionic basis of electrical alterations in small intestinal epithelium of the guinea pig during in vitro anaphylaxis. Results suggest that Cl('-) secretion mediated, in part, by cAMP contributes to antigen-induced jejunal ion transport changes and that histamine and prostaglandins are involved in eliciting epithelial responses. ^