Limiting dilution analysis of the frequency of antigen-reactive lymphocytes isolated from the central nervous system of Lewis rats with experimental allergic encephalomyelitis

Lymphocytes were isolated from the spinal cord and draining lymph nodes of Lewis rats with acute experimental allergic encephalomyelitis (EAE) 12 days after immunization with myelin basic protein (MBP) and tetanus toxoid (TT). An average of 8.0 +/- 2.0 X 10(6) cells was obtained from the spinal cord. Of these 71.1 +/- 8.6% expressed the helper-T-cell marker W3/25 and 14.8 +/- 6.2% expressed the killer/suppressor-T-cell marker OX8. By limiting dilution analysis of cells exhibiting an antigen-specific proliferative response, the average frequencies of cells reactive to MBP and TT were 3.36 +/- 2.4 and 7.60 +/- 4.1 per 10(4), respectively. In the draining lymph nodes, the frequencies of cells reactive to MBP and TT were 2.24 +/- 1.7 and 2.69 +/- 2.5 per 10(4). At a relatively early stage of clinical EAE, MBP-reactive T cells comprise only a small minority of the cells which can be isolated from the spinal cord; lymphocytes reactive to a protein antigen irrelevant to EAE pathogenesis are present in comparable numbers. This finding suggests that most of these cells accumulate as a result of mechanisms not specific for MBP-reactive lymphocytes.     

Recipient competence in F''lac matings of Escherichia coli K-12.

We studied recipient mating ability in the presence of excess F'lac donors. Ninety-five percent of recipients were able to receive F'lac in 30-min matings. Competition between an F'-lac donor and an F'lac traI donor, which mobilized a ColE1 derivative (pML2), showed that each recipient mated with an average of two to three donors in 30 min. Experiments in which the competing donor was added at different times showed that some competition occurred throughout the 30-min mating period, which suggested that aggregate formation was spread over this time.     

Leucostasis, an underestimated cause of death in leukaemia

Massive sludging of leukaemic cells in blood vessels is a frequent and often lethal complication of leukaemia. In a retrospective clinicopathological study on the causes of death in 52 patients with acute myeloid leukaemia and myeloproliferative disease, pulmonary leucostasis was found in 40% of the patients. In many of these patients the vessels of the heart, brain and testes were also involved. In search for signs and symptoms specific for leucostasis, the clinical records of the 21 patients with leucostasis (the study group) were compared to those of 20 patients without leucostasis (the control group). Dysfunction of the organs most affected by leucostasis, namely lungs, heart and brain, was found more often in the study group than in the controls, but the combination of unexplained fever with cardiopulmonary and/or central nervous system failure occurred almost exclusively and in half of the patients with leucostasis. Leucostasis occurs predominantly, but not exclusively, in patients with high leucocyte counts, and especially, but again not exclusively, when the leucocyte counts rise sharply.     

The heparin binding domain of S-protein/vitronectin binds to complement components C7, C8, and C9 and perforin from cytolytic T-cells and inhibits their lytic activities

S-Protein/vitronectin is a serum glycoprotein that inhibits the lytic activity of the membrane attack complex of complement, i.e., of the complex including the proteins C5b, C6, C7, C8, and C9n. We show that intact S-protein/vitronectin or its cyanogen bromide generated fragments also inhibit the hemolysis mediated by perforin from cytotoxic T-cells at 45 and 11 microM, respectively. The glycosaminoglycan binding site of S-protein/vitronectin is responsible for the inhibition, since a synthetic peptide corresponding to a part of this highly basic domain (amino acid residues 348-360) inhibits complement- as well as perforin-mediated cytolysis. In the case of C9, the synthetic peptide binds to the acidic residues occurring in its N-terminal cysteine-rich domain (residues 101-111). Antibodies raised against this particular segment react 25-fold better with the polymerized form of C9 as compared with its monomeric form, indicating that this site becomes exposed only upon the hydrophilic-amphiphilic transition of C9. Since the cysteine-rich domain of C9 has been shown to be highly conserved in C6, C7, and C8 as well as in perforin, the inhibition of the lytic activities of these molecules by S-protein/vitronectin or by peptides corresponding to its heparin binding site may be explained by a similar mechanism.     

Cleavage of dT8 and dT8 phosphorothioyl analogues by Escherichia coli DNA topoisomerase I: product and rate analysis

Escherichia coli DNA topoisomerase I catalyzes the cleavage of short, single-stranded oligodeoxynucleotides with dT8 as the shortest cleavable oligo(thymidylic acid). The 5'-32P-labeled products formed from the cleavage of [5'-32P]dT8 are dT5, dT4, and dT3 with over 70% of the substrate cleaved to dT4. Mg(II) ions affect this product distribution by increasing the percentage of dT4 formed. The substitution of a sulfur atom for a nonbridging oxygen atom in a phosphodiester linkage yields oligodeoxynucleotide phosphorothioyl (PS) analogues. The epimers of the analogues were separated, and the position and stereochemistry of the phosphorothiodiester bond were determined. Topoisomerase I is stereospecific in its reactivity toward these analogues. With the oligodeoxynucleotide PS analogue substrates, the rate of cleavage, the stereospecificity, and the product distribution depend upon the position and the stereochemistry of the phosphorothiodiester linkage.     

Cytotoxic and antiprotozoal activity of flavonoids from Lonchocarpus spp.

A number of flavonoids isolated from Lonchocarpus spp. were evaluated for their antiprotozoal and cytotoxic activity. Flavone 6 and chalcone 7 were found to be the most active against Leishmania parasites and against cell cultures of Leukemia P388DI and adenocarcinoma prostate PC-3.