Influence of chronic antigen exposure on the metabolism of PGH2 by microsomal preparations of airway and parenchymal tissues in the sheep

The effects of repeated antigen exposure on the synthesis of mediators by lung tissues are not well understood. To investigate the influence of antigen challenge on the synthesis of prostaglandins by central airway and peripheral lung tissues, fourteen sensitive sheep underwent biweekly exposure to aerosolized $\text{Ascaris suu}$ antigen (7) or saline (7). Following the fifth exposure, microsomal and high speed supernatant fractions were prepared from trachealis muscle and lung parenchyma. Synthesis of thromboxane (TX) A₂, prostaglandin (PG) D₂ and PGI₂ from the PG endoperoxide intermediate, PGH₂, was assayed over a range of substrate concentrations from 3–200 uM. Synthesis of PGI₂ by trachealis microsomes was approximately 5-fold greater than that of TXA₂. PGI₂ and TXA₂ production was identical in tracheal preparations from Ascaris- and saline-exposed animals. In parenchymal tissues, where TXA₂ production predominated over PGI₂ by 9-fold, preparations from Ascaris- exposed animals synthesized 50% more TXA₂ than controls at PGH₂ concentrations of 25 uM and above, whereas synthesis of PGI₂ and PGD₂ were similar in preparations from both groups of animals. The density of pulmonary mast cells was decreased by 21% in the Ascaris group, whereas polymorphonuclear leukocyte density was unchanged. These results demonstrate the differential synthesis of TXA₂ and PGI₂ in central airways and peripheral lung regions of the sheep. They further indicate that repeated exposure of the airways to antigen selectively enhances TXA₂ synthesis in the lung periphery of sensitized animals. The site of this increased enzymatic activity, whether in resident cells or newly-infiltrated cells, has not been determined.     

The role of the cysteine-rich region of the β2 integrin subunit in the leukocyte function-associated antigen-1 (LFA-1, αLβ2, CD11a/CD18) heterodimer formation and ligand binding

The cysteine-rich region (CRR) of the β2 integrin subunit was replaced by that of β1 to give the chimera β2NV1. β2NV1 can combine with αL to form a variant leukocyte-function-associated antigen (LFA)-1 on COS cell surface, suggesting that the specificity of the β2 interaction with αL does not lie in the CRR. Unlike those expressing wild-type LFA-1, COS cells expressing αLβ2NV1 are constitutively active in intercellular adhesion molecule (ICAM)-1 adhesion. These results suggest that activation of LFA-1 involves the release of an intramolecular constraint, which is maintained, in part, by the authentic β2 CRR.     

Structure of Haze Forming Proteins in White Wines: Vitis vinifera Thaumatin-Like Proteins

Grape thaumatin-like proteins (TLPs) play roles in plant-pathogen interactions and can cause protein haze in white wine unless removed prior to bottling. Different isoforms of TLPs have different hazing potential and aggregation behavior. Here we present the elucidation of the molecular structures of three grape TLPs that display different hazing potential. The three TLPs have very similar structures despite belonging to two different classes (F2/4JRU is a thaumatin-like protein while I/4L5H and H2/4MBT are VVTL1), and having different unfolding temperatures (56 vs. 62°C), with protein F2/4JRU being heat unstable and forming haze, while I/4L5H does not. These differences in properties are attributable to the conformation of a single loop and the amino acid composition of its flanking regions.     

Maleylated-BSA suppresses IFN-gamma-mediated Ia expression in murine peritoneal macrophages

Maleylated bovine serum albumin (maleyl-BSA) and other polyanionic polymers that are recognized by cell surface receptors on macrophages have been shown to induce chemotaxis, protease secretion, and tumoricidal function in this cell type. In this paper the effect of maleyl-BSA on Ia antigen expression has been evaluated. In a fashion similar to LPS, maleyl-BSA suppressed IFN-gamma-induced expression of Ia in a time- and dose-dependent manner. Also like LPS, maleyl-BSA stimulated the production and secretion of substantial amounts of PGE2 over a 24-hr period. This did not, however, appear to be the primary mechanism by which expression of Ia was suppressed, because co-treatment of the cells with indomethacin, which totally inhibited the production of PGE2, only minimally affected the suppressive activity. Surprisingly, the suppressive activity of both maleyl-BSA and LPS could be largely abrogated by co-treatment of the cells with cyclohexamide during the time period when Ia expression was sensitive to suppression. This effect was selective in that PGE2- or dibutyryl cyclic AMP-induced suppression of Ia expression was not affected by cyclohexamide treatment. The data support the concept that there are multiple molecular mechanisms involved in the negative regulation of IFN-gamma-induced Ia expression in macrophages. Such mechanisms may include, in addition to the synthesis of PGE2 and consequent elevation in intracellular levels of cyclic AMP, one or more proteins made early after treatment with either maleyl-BSA or LPS. Thus the function of some of these early gene products may be to regulate expression of functional genes such as that encoding Ia antigen.     

On the mechanism by which dopamine inhibits prolactin release in the anterior pituitary

An $\text{in}$$\text{vitro}$ perfusion system was used to assess the effects of chloride channel blockers, dopamine (DA) receptor agonists and antagonists, and GABA receptor agonists and antagonists on prolactin release from the mouse anterior pituitary. Dopamine and muscimol inhibited prolactin release ($\text{IC}{}_{50}{}^1\text{= 6 × 10}{}^{\mathrm{?8}}\text{M and}\text{10}{}^{\mathrm{?5}}\text{M}$ respectively). The GABA receptor antagonist bicuculline blocked the inhibition of prolactin release by muscimol but not dopamine. The dopamine receptor antagonist chlorpromazine blocked the dopamine- but not muscimol-induced inhibition of prolactin release. Haloperidol, however, reversed both the muscimol and dopamine induced inhibition of prolactin release. Furthermore, the chloride channel blocker picrotoxinin blocked the inhibition of prolactin release elicited by both dopamine and muscimol. These later results suggest that the anterior pituitary dopamine receptor which mediates the inhibition of prolactin release may be coupled to a picrotoxinin sensitive chloride ionophore and that haloperidol may affect the function of both DA and GABA receptors in the anterior pituitary.