Reduced immunoglobulin G activates complement system with decreased cooperativity

Sheep erythrocytes sensitized with intact antibody or reduced and alkylated antibody were lysed by guinea-pig serum indicating that reduced and alkylated antibody bound and activated complement. Reduction of antibody caused erythrocyte lysis to exhibit pseudo-first-order kinetics, while the lysis kinetics of erythrocytes sensitized with intact antibody was sigmoidal. Analysis of erythrocyte lysis by complement according to the von Krogh equation showed that reduction of antibody diminished the von Krogh exponent $\text{n}$ from 2.8 to 1.3, while the value of $\text{K}$ remained unchanged at 0.17 (complement dilution). These observations suggested that the sole effect of the reduction of antibody inter-heavy-chain and heavy-light chain disulfide bonds was to diminish the cooperativity of antibody-complement interaction.     

The mouse Fc receptor for IgG (Ly-17) : molecular cloning and specificity

A cDNA clone encoding the mouse Ly-17⁺ Fc receptor for IgG, isolated from a myelomonocytic cell line, was sequenced and expression of mRNA and the functional FcR investigated. The receptor is a 301 amino acid transmembrane glycoprotein with two homologous extracellular domains that are also homologous to members of the Ig superfamily. The receptor has four sites of N-linked glycosylation and a long 94 amino acid cytoplasmic tail. Northern analysis, immune complex binding, and serological studies demonstrate that the receptor encoded by the cDNA clone binds mouse IgG_1/2b and rabbit IgG complexes.     

Decreased brown adipose tissue thermogenic activity following a reduction in brain serotonin by intraventricular p-chlorophenylalanine

The effects of reducing brain serotonin (5-HT) levels by means of intracerebral-ventricular injections of the tryptophan antagonist p-chlorophenylalanine (PCPA) were investigated in male rats. Six days after the operation, PCPA-treated rats, either fedad libitum or pair-fed to the food intake of control rats, showed decreased thermogenic activity and capacity in their interscapular brown adipose tissue (BAT) and also increased fat storage in their white adipose tissue (WAT). These results indicate that serotonergic synapses might play a regulatory role in the sympathetic control of BAT thermogenesis and in the rate of WAT deposition (by an as yet unidentified mechanism), in addition to their well established role in controlling food intake.     

The response of the intestinal epithelium in B10.A mice to infection with Trichinella spiralis

Previous studies on intestinal trichinosis have dealt mainly with areas other than the intestinal epithelium. Since the epithelium is now known to be the parasite's habitat, its response to infection is important. Infection with Trichinella spiralis in immunologically slow-responding B10.A mice was associated with crypt hyperplasia and villus atrophy. With similar infection levels in both primary and challenge infections, there was no difference in the maximal degree of atrophy or hyperplasia between the 2 groups. However, challenged mice underwent these mucosal changes in about half the time. Expulsion of worms always occurred during regeneration of the intestinal epithelium suggesting that the host's defense mechanism of altering the kinetics of the epithelium was not the prime factor causing expulsion. Pulse labelling of enterocytes with [3H] thymidine showed that there was no significant increase in the relative size of the proliferation zone. This indicates that the crypt cell output was not altered by this parasite. Atrophy of the villus was analysed with respect to its 3-dimensional shape. There was a decrease in both height and width of the villus but not thickness. Thus, there is a real decrease in the size of the enterocyte population per villus. Histochemical staining of the enterocyte brush border by an alkaline phosphatase method showed that (1) hyperplastic crypts have an enlarged maturation zone and (2) the villus epithelium is composed entirely of mature cells. The distribution of the nematode population was compared to these changes in the intestine. Trichinella spiralis showed a marked anteriad (distal to proximal) migration prior to expulsion. Thus, utilizing a novel approach to study intestinal trichinosis, the response of the mucosal epithelium has been characterized.     

Effects of diclofop and diclofop-methyl on the membrane potentials of wheat and oat coleoptiles

Electrophysiological measurements were made on the mesophyll cells of wheat (Triticum aestivum L. cv Waldron) and oat (Avena sativa L. cv Garry) coleoptiles treated either with the herbicide diclofop-methyl (methyl 2-(4-(2′,4′-dichlorophenoxy)phenoxy)propanoate), or it's primary metabolite diclofop, (2-(4-(2′,4′-dichlorophenoxy)phenoxy)-propanoic acid). Application of a 100 micromolar solution of diclofop-methyl to wheat coleoptiles had little or no effect on the membrane potential (E_M), however in oat, E_M slowly depolarized to the diffusion potential (E_D). At pH 5.7, 100 micromolar diclofop rapidly abolished the electrogenic component of the membrane potential in both oat and wheat coleoptiles with half-times of 5 to 10 minutes and 15 to 20 minutes, respectively. The concentrations giving half-maximal depolarizations in wheat were 20 to 30 micromolar compared to 10 to 20 micromolar in oat. The depolarizing response was not due to a general increase in membrane permeability as judged from the E_M's response to changes in K⁺, Na⁺, Cl⁻, and SO₄²⁻, before and after treatment with diclofop and from its response to KCN treatment. In both plants, diclofop increased the membrane permeability to protons, making the E_M strongly dependent upon the external pH in the range of pH 5.5 to pH 8.5. The effects of diclofop can best be explained by its action as a specific proton ionophore that shuttles protons across the plasmalemma. The rapidity of the cell's response to both diclofop-methyl (15-20 minutes) and diclofop (2-5 minutes) makes the ionophoric activity a likely candidate for the earliest herbicidal event exhibited by these compounds.     

Structural consequences of heme isomerism in monomeric hemoglobins from Glycera dibranchiata

Two-dimensional 1H-NMR methods have been used to assign heme and amino acid proton resonances in both isomeric states of the carbon monoxide complexes of two Glycera dibranchiata monomeric hemoglobins, HbA and HbB. For each hemoglobin, there are small differences in heme pocket structure in the two isomeric forms. The largest structural perturbations associated with heme isomerism involve residues close to pyrrole rings I and II. The positions relative to the heme of phenylalanine CD1 and the proximal histidine ligand are almost unaffected by heme isomerism. These residues probably play a key role in determining the location of the heme within the heme pocket.