[Preliminary investigation on reservoir hosts of Borrelia burgdorferi in China]

From 1987 to 1997, the reservoir hosts of Borrelia burdorferi(B.b.) were investigated in 16 provinces, municipalities and autonomous regions of China. Seroepidemiological findings indicated that cattle, sheep, dogs and rats from forest areas had a high antibody titer for B.b. (B31) with positive rates of 18.18%-32.61%, 17.12%-61.21%, 38.50-60.00% and 41.18%-86.05% respectively. Using BSK medium, 20 strains of B.b. were isolated from Apodemus agrarius, Clethrionomys rufocanus, Eutamias sibiricus, Rattus coxingi, Rattus norvegicus, Rattus edwardsi, Rattus confucianus, Rattus fulvescens and Caprolagus sinensis. These spirochetal strains were identified as B.b. by indirect immunofluorescence assay using species and genus specific monoclonal antibodies. Vertical transmission of B.b. was confirmed with B.b. isolated from foetuses of Apodemus agrarius and Rattus edwardsi. The results showed that lyme disease spirochetes, B.b., might be naturally maintained in an enzootic cycle by transplacental transmission. Apodemus agrarius and Clethrionomys rufocanus might serve as major reservoir hosts for B.b. in China.

[Investigation on primary vectors of Borrelia burgdorferi in China]

From 1987 to 1997, primary vectors of borrelia burgdorferi sensu lato (B.b.s.l.) were investigated in China. A total number of 17,000 ticks collected from 20 provinces, city and autonomous region were classified, including 2 families 8 genus 23 species. There were 108 isolates of B.b.s.l. discovered from 8 species of ticks, including Ixodes persulcatus, I. granulatus, I. acutitarsus, Haemaphysalis concinna, H. longicornis, H. bispinosis, H. cornigera taiwana and Dermacentor silvarum. Ixodes persulcatus was found as the dominant species, accounted for more than 80% of the total number of collected ticks. 20 to 45 per cent adult Ixodes persulcatus contained spirochetes as determined by direct immunofluorescence in the northeast and northwest areas. Seasonal change of adult Ixodes persulcatus was coincident with patients with erythema chronicum migrans. These studies proved that Ixodes persulcatus played a leading role in the transmission of B.b.s.l. to human being in northern region of China. Haemaphysalis bispinosis and Ixodes granulatus were identified as the dominant species with 16 to 40 per cent adult Haemaphysalis bispinosis and 24% per cent adult Ixodes granulatus containing spirochetes as determined by direct immunofluorescence in the southern region of China. Haemaphysalis bispinosis and Ixodes granulatus were proved to be important vectors of B.b.s.l. in the southern area of China.

[Study on the elimination of bacteria from the cultures of Lyme disease spirochetes (Borrelia burgdorferi)]

Contaminated cultures of strains H11, H20 from ticks, and strain R9 from patient were purified by antisera for bacteria, chemicals, filtration dilution and animal inoculation. Most of bacteria were eliminated after adding antisera into contaminated strains H11, H20. The preliminarily decontaminated cultures of strains H11, H20 or those with a few bacteria such as strain R9 could be completely purified by filtration, chemicals, dilution, or animal inoculation, but filtration is the simplest and the most effective purification method.

Structural heterogeneity of the alpha subunits of the nicotinic acetylcholine receptor in relation to agonist affinity alkylation and antagonist binding

The structural basis for the heterogeneity of the two agonist binding sites of the Torpedo californica acetylcholine receptor with respect to antagonist binding and reactivity toward affinity alkylating reagents was investigated. There is one agonist binding site on each of the two alpha subunits in a receptor monomer. One of these sites is easily affinity labeled with bromoacetylcholine, while more extreme conditions are required to label the other. Evidence is presented that the site which is easily labeled with bromoacetylcholine is the site with higher affinity for the antagonist d-tubocurarine. Digestion of purified alpha subunits with staphylococcal V8 protease gave two limit fragments with apparent molecular weights of 17K and 19K. Both of these fragments began at residue 46 of the alpha sequence, and both reacted with monoclonal antibodies specific for the sequence alpha 152-159 but not with antibodies specific for alpha 235-242. Their tryptic peptide maps and reactivity with a number of monoclonal antibodies were virtually identical. Only the 17-kilodalton (17-kDa) fragments stained heavily for sugars with Schiff's reagent. However, both fragments bound 125I-labeled concanavalin A. Complete removal of carbohydrate detectable with concanavalin A from V8 protease digests of alpha subunits resulted in two fragments of lower apparent molecular weights, indicating that these fragments differed not only in carbohydrate content but also in their C-termini or by another covalent modification. Covalent labeling of one of the two agonist sites of the intact receptor with bromo[3H]acetylcholine followed by digestion with V8 protease resulted in labeling of only the 19-kDa fragment.(ABSTRACT TRUNCATED AT 250 WORDS)

Single-channel recordings from purified acetylcholine receptors reconstituted in bilayers formed at the tip of patch pipets

The channel of the purified acetylcholine receptor from Torpedo californica electric organ reconstituted in lipid vesicles was assayed by direct electrical recording using patch-clamp pipets. High-resistance seals were obtained by gentle suction of vesicles into the pipet or after the formation of lipid bilayers from monolayers at the tip of the pipet. Single-channel currents were activated by three cholinergic ligands: acetylcholine, carbamylcholine, and suberyldicholine. The single-channel conductance, gamma, was 40 +/- 5 pS in 0.5 M NaCl, irrespective of the agonist used. The distributions of channel open times were fitted by a sum of two exponentials. The lifetimes of the two exponential components were a factor of 2 longer for suberyldicholine than for acetylcholine or carbamylcholine. At desensitizing concentrations of agonists the single events appeared in paroxysms of channel activity followed by quiescent periods. These results suggest that the full cycle of solubilization, purification, and reconstitution of this membrane receptor can be achieved without impairment of channel function.

Interaction of Sindbis virus glycoproteins during morphogenesis

In cells infected with the Sindbis temperature-sensitive mutants ts-23 and ts-10 (complementation group D), which contain a defect in the envelope glycoprotein E1, the precursor polypeptide PE2 is not cleaved to the envelope glycoprotein E2 at the nonpermissive temperature. This defect is phenotypically identical to the defect observed in the complementation group E mutant, ts-20. The lesion in ts-23 is reversible upon shift to permissive temperature, whereas that of ts-10 is not. Antiserum against whole virus, E1, or E2 also prevents the cleavage of PE2 in cells infected with wild-type Sindbis virus. Because the cleavage of PE2 is inhibited by the lesion in mutants that are genotypically distinct and by anti-E1 or -E2 serum, it appears that PE2 and E1 exist as a complex in the membrane of the infected cell.

Homologous interference induced by Sindbis virus

Homologous interference during Sindbis virus infection has been investigated. Prior infection of either chicken embryo fibroblast or BHK(21) cell cultures results in reduced yields of progeny virions of the superinfecting genotype. This reduction in yield results from a reduction in the number of cells in the cultures capable of producing the superinfecting genotype. The development of interference parallels the attachment kinetics of Sindbis virus. Interference requires an active viral genome since the activity is sensitive to inactivation by ultraviolet light, and an RNA(-) mutant, ts-24, fails to induce interference under nonpermissive conditions. However, ts-6, an RNA(-) mutant belonging to a different complementation group, and the RNA(+) mutants, ts-2 and ts-20, interfere at both permissive and nonpermissive temperatures.