The presence of maternal antibodies protected suckling C57BL/6 mice from the clinical manifestations of the acute encephalomyelitis caused by mouse hepatitis virus, strain JHM (MHV-JHM), a coronavirus, even though histological evidence of encephalomyelitis was found at early times after inoculation. 100% of infected suckling mice developed a fatal disease in the absence of maternal antibody. By 14 days after inoculation, the brains of all antibody-protected mice examined were nearly normal on histological examination. At 3-8 weeks post-inoculation, approximately 40% of the antibody-protected mice developed a neurological disease characterized by hindlimb paralysis and wasting. Evidence of inflammation and demyelination was apparent in the spinal cord and brainstem. The mice that remained asymptomatic at this time showed few signs of inflammation and none developed clinical disease over the following 9 months. Viral antigen could be detected in most of the mice examined at all times after inoculation, whether symptomatic or not, and was particularly evident in the animals with hindlimb paralysis. MHV-JHM could be consistently cultured from the mice with hindlimb paralysis. These results show that maternal immune factors can completely protect susceptible mice from the acute, fatal, clinical encephalomyelitis caused by MHV-JHM, but cannot prevent the establishment of a latent state and subsequent development of virus-induced, clinically evident, demyelinating disease. This model will be useful for studying the virus and host factors important for the development of MHV-JHM latency and subsequent virus-induced demyelination.

Histamine increases microvascular permeability by creating small transitory (100-400 nm) gaps between adjacent endothelial cells at sites of vascular endothelial (VE)-cadherin-based adhesion. We examined the effects of histamine on the proteins within the VE-cadherin-based adherens junction in primary human umbilical vein endothelial cells. VE-cadherin is linked not only by beta- and alpha-catenin to cortical actin but also by gamma-catenin to the intermediate filament vimentin. In mature human umbilical vein cultures, the VE-cadherin immunoprecipitate contained equivalent amounts of alpha- and beta-catenin, 130% as much beta- as gamma-catenin, and 50% as much actin as vimentin. Within 60 s, histamine decreased the fraction of VE-cadherin in the insoluble portion of the cell lysate by 35 +/- 1.5%. At the same time, histamine decreased the amount of vimentin that immunoprecipitated with VE-cadherin by 50 +/- 6%. Histamine did not affect the amount of actin or the amount of alpha-, beta-, or gamma-catenin that immunoprecipitated with VE-cadherin. Within 60 s, histamine simulated a doubling in the phosphorylation of VE-cadherin and beta- and gamma-catenin. The VE-cadherin immunoprecipitate contained kinase activity that phosphorylated VE-cadherin and gamma-catenin in vitro.

During the immediate response to an inhaled allergen, there is an increase in the paracellular permeability of the airway epithelium.1 Histamine is an important agonist released during the immediate response to inhaled allergen. We hypothesized that histamine would increase human airway epithelial paracellular permeability and that it would do this by interrupting E-cadherin-based cell adhesion. Histamine, applied to the basolateral surface, increased the paracellular permeability of cultured human airway epithelia, and this effect of histamine was blocked by the histamine receptor antagonist promethazine. ECV304 cells express a histamine receptor, N-cadherin, and elements of the tight junction, including claudins, but they do not express E-cadherin. Histamine increased the paracellular permeability of ECV304 cells transfected with a vector and expressing E-cadherin but not ECV304 cells expressing lac-Z in the same vector. L cells do not express the histamine receptor, cadherins, or claudins. Histamine decreased adhesion of L cells expressing the human histamine receptor and E-cadherin to an E-cadherin-Fc fusion protein. Histamine did not alter the adhesion to the E-cadherin fusion protein of L cells expressing either the histamine receptor or E-cadherin alone. When applied to the apical surface, adenovirus poorly infects airway epithelial cells because its receptor, CAR, is restricted to the basolateral surface of the cells. When histamine was applied to the basolateral surface of airway epithelial cells, infection of the cells by adenovirus increased by approximately one log. This effect of histamine was also blocked by promethazine. Histamine increases airway paracellular permeability and increases susceptibility of airway epithelial cells to infection by adenovirus by interrupting E-cadherin adhesion.

The airway epithelium is an important barrier between the environment and subepithelial tissues. The epithelium is also divided into functionally restricted apical and basolateral domains, and this restriction is dependent on the elements of the barrier. The protease-activated receptor-2 (PAR2) receptor is expressed in airway epithelium, and its activation initiates multiple effects including enhanced airway inflammation and reactivity. We hypothesized that activation of PAR2 would interrupt E-cadherin adhesion and compromise the airway epithelial barrier. The PAR2-activating peptide (PAR2-AP, SLIGRL) caused an immediate approximately 50% decrease in the transepithelial resistance of primary human airway epithelium that persisted for 6-10 min. The decrease in resistance was accompanied by an increase in mannitol flux across the epithelium and occurred in cystic fibrosis transmembrane conductance receptor (CFTR) epithelium pretreated with amiloride to block Na and Cl conductances, confirming that the decrease in resistance represented an increase in paracellular conductance. In parallel experiments, activation of PAR2 interrupted the adhesion of E-cadherin-expressing L cells and of primary airway epithelial cells to an immobilized E-cadherin extracellular domain, confirming the hypothesis that activation of PAR2 interrupts E-cadherin adhesion. Selective interruption of E-cadherin adhesion with antibody to E-cadherin decreased the transepithelial resistance of primary airway epithelium by >80%. Pretreatment of airway epithelium or the E-cadherin-expressing L cells with the long-acting beta-agonist salmeterol prevented PAR2 activation from interrupting E-cadherin adhesion and compromising the airway epithelial barrier. Activation of PAR2 interrupts E-cadherin adhesion and compromises the airway epithelial barrier.

We tested the hypothesis that histamine alters the focal apposition of endothelial cells by acting on sites of cadherin-mediated cell-cell adhesion. Focal apposition was measured as the impedance of a cell-covered electrode, which was partitioned into a cell-matrix resistance, a cell-cell resistance, and membrane capacitance. Histamine causes an immediate, short-lived decrease in the impedance of an electrode covered with human umbilical vein endothelial (HUVE) cells. ECV304 cells are a line of spontaneously transformed HUVE cells that do not express the endothelial cadherin, cadherin-5. Histamine increased ECV304 cell calcium to 600 nM. Histamine did not increase myosin light chain phosphorylation of control or transfected ECV304 cells. ECV304 cells transfected with either E-cadherin or cadherin-5 on a dexamethasone-responsive plasmid (pLKneo) increased their cell-cell resistance when stimulated with dexamethasone, whereas ECV304 cells transfected with pLKneo-lacZ did not. Histamine did not affect the impedance of ECV304 cells transfected with pLKneo-lacZ. In contrast, histamine decreased the cell-cell resistance of ECV304 cells transfected with either pLKneo-E-cadherin or pLKneo-cadherin-5. From these data, we conclude that histamine acts on sites of cadherin-mediated cell-cell apposition.