Polymorphism and complexity of HLA-DR: evidence for intra-HLA-DR region crossing-over events

HLA-DR molecules were isolated from HLA-DR3, –5, and –w6 positive homozygous B-cell lines by immunoprecipitation with monoclonal antibodies and analyzed by gel electrophoretic techniques. DNA isolated from the same cell lines was digested with the restriction enzyme Taq I and hybridized with a DR beta full-length cDNA probe. We demonstrated that certain DR I alleles are found in combination with different DR III alleles as defined by Southern blotting, protein chemistry, a functional assay using purified protein derivative-specific T-cell lines, and, in one case, also alloreactive T-cell reagents. Our results indicate that within the family of HLA-DRw52-associated haplotypes DR beta chain genes may have been transferred from one haplotype to another. The implications of these findings are discussed.     

Foraging for patchily-distributed leaf miners by the parasitic wasp,Dacnusa sibirica

We studied the rules used by the female parasitoid, Dacnusa sibirica Telenga (Hymenoptera: Braconidae), for deciding when to leave a tomato leaflet on which she is searching for larvae of the leafminer, Liriomyza bryoniae Kalt. (Diptera: Agromyzidae). Females would deposit a marking pheromone on the leaflet and would leave the leaflet when the amount of the pheromone accumulated to the threshold L, which is proportional to the amount of search effort on the leaflet. L appears to increase with host density since it rises after every encounter with a host (or mine).D. sibirica would employ an area-concentrated search, which is advantageous in foraging for hosts showing a clumped distribution.     

Apolipoprotein A-I binds to a family of bovine seminal plasma proteins

Bovine seminal plasma contains four similar acidic proteins, previously designated as BSP (bovine seminal plasma)-A1, BSP-A2, BSP-A3, and BSP-30-kDa, that when added to pituitary cell cultures result in the immediate secretion of gonadotropins (follitropin and lutropin). However, when calf or horse serum was included in the culture medium the secretion of gonadotropins was completely prevented. This effect was seen at levels up to 200 micrograms of BSP protein/ml while the presence of more than 200 micrograms of BSP protein/ml in the serum medium continued to release gonadotropins. This could be explained by the presence in the sera of a binding factor to the BSP proteins which prevents their action. This binding factor has been detected in all the sera tested, including human serum, in dot-blot experiments using 125I-labeled BSP-A1, -A2, -A3, or -30-kDa protein. Thus, it was of interest to isolate this binding factor from human serum by affinity chromatography on a column of BSP-A1/-A2-agarose. The purified binding factor was then identified as apolipoprotein A-I (apoA-I) by the following criteria: (a) it has a molecular mass of 27,000 daltons, (b) the amino acid composition is similar to apoA-I, (c) the first 25 residues at the amino-terminal end of this binding factor are identical to apoA-I, and (d) the binding factor cross-reacts in the radioimmunoassay of apoA-I. Furthermore, BSP proteins also bind to purified plasma apoA-I and apoA-I associated with high density lipoprotein. ApoA-I is the major protein of plasma high density lipoprotein and plays an important role in lipid transport and metabolism. Thus, the binding of bovine seminal plasma proteins to apoA-I suggests some physiological significance in lipoprotein function or vice versa.     

A potential complication in the use of monoclonal antibodies: inhibition of apoB-mediated receptor binding by an anti-apoE antibody

Monoclonal antibody (Mab) 1D7 is specific for human apolipoprotein (apo) E and blocks binding of lipid-associated apoE to the low density lipoprotein (LDL) receptor. We report here that 1D7 can also block the binding of apoE-free LDL to the LDL receptor. The inhibition of LDL-receptor binding is not due to immunological cross-reactivity between the anti-apoE Mab and apoB, the ligand responsible for the interaction of LDL with the LDL receptor: 1) Mab 1D7 did not react with apoE-depleted LDL; 2) the LDL receptor binding inhibitory activity of 1D7 immunoglobulin G (IgG) preparations could be dissociated from the anti-apoE activity; 3) the inhibition was maintained when the fibroblasts were preincubated with the 1D7 IgG, extensively washed, and only then exposed to 125I-labeled LDL. Rather, it appears that 1D7 recognizes mouse apoE, that mouse apoE-1D7 immune complexes contaminate 1D7 IgG preparations and that the contaminating mouse apoE can compete with 125I-labeled LDL for the LDL receptor. We have demonstrated mouse apoE in IgG preparations of 1D7 but not in those of other anti-apoE Mabs that do not influence LDL-receptor binding. Precipitation of 1D7 IgG with NH4SO4 eliminates both apoE and the capacity of 1D7 to block LDL receptor binding. Finally, mouse apoE can be isolated by immunoaffinity chromatography of mouse serum on immobilized 1D7 Mab. As this is probably not a unique case, the observation has important implications for the use of Mabs as structural probes.     

An immunochemical marker of low density lipoprotein oxidation

Using monoclonal antibodies against apolipoprotein B (apoB) we studied changes in apoB immunoreactivity during copper ion-mediated oxidation of human low density lipoprotein (LDL). The radioimmunoassay experiments demonstrated the decrease of immunoreactivity of three different epitopes of apoB located in different parts of the protein; at the same time the immunoreactivity of another epitope, previously mapped to the C-terminal 20 amino acids of apoB increased markedly during the first 6 h of LDL oxidation and diminished gradually upon prolonged incubation with copper ions. The fate of LDL during oxidation was also monitored using electrophoretic techniques combined with immunodetection. These experiments showed a rapid fragmentation and disappearance of immunoreactive apoB. They also indicated that the diminishing LDL immunoreactivity detectable during oxidation is associated with apoB fragments still attached to the lipid core. The changes in apoB immunoreactivity during Cu2+ treatment of LDL are similar to those observed upon LDL aging. Therefore, it appears that the enhancement of immunoreactivity of the C-terminus of apoB is a general phenomenon associated with various kinds of oxidative modifications of LDL.     

Trisomy 11p15 and Beckwith-Wiedemann syndrome. A report of two cases

Summary Two patients with trisomy 11p15 and features of Beckwith-Wiedemann syndrome are reported. The first is a female infant with gigantism, macroglossia, abdominal hypotonia with umbilical hernia, moderate mental retardation, malformative uropathy, and atrial septal defect. Trisomy 11p15 was due to de novo duplication. The second patient was a stillborn (32–33 weeks pregnancy) with an abnormal tongue, posterior diaphragmatic eventration, inner organ congestion mainly of the adrenals. Trisomy 11p15 was due to a t(4;11)(q33;p14)pat. The association of trisomy 11p15 and Beckwith-Wiedemann syndrome is discussed with regard to cytogenetic data and the gene content of 11p, notably the genes coding for insulin and predisposition to Wilms tumour.     

The effect of rearing history and aphid density on volatile‐mediated foraging behaviour of Diaeretiella rapae

1. Parasitoid females foraging for hosts rely on cues derived from the insect host, the host plant and/or their interaction, and all of these can be learned during the immature and adult stages. 2. The present study investigated the importance of rearing history on foraging behaviour of Diaeretiella rapae, an endoparasitoid often associated with aphids feeding on brassicaceous plant species. 3. Parasitoids were reared on one of the four possible combinations, comprising two brassicaceous host plant species, Brassica nigra or Raphanus sativus, and two aphid species Brevicoryne brassicae or Myzus persicae. These parasitoids were tested in a Y‐tube olfactometer and given the choice between volatiles emitted by an aphid‐infested plant (25 or 100 aphids per plant) and an uninfested control plant. The parasitoid's responses were compared when offered: (i) the same plant–aphid combination as the one on which it had been reared; (ii) the same host plant infested with the alternative aphid species; or (iii) an alternative plant with the alternative aphid species. 4. Aphid density did affect the behavioural responses to the various odour sources, but rearing history did not. Diaeretiella rapae only preferred aphid‐induced to non‐induced plant volatiles at low aphid infestation level, whereas they did not discriminate between volatiles at high aphid infestation level. 5. It is concluded that aphid‐induced volatiles of brassicaceous plants play an important role during host habitat location, but seem less important for parasitoids to locate the aphid host itself. The data are discussed in the light of manipulation of host plant defences by aphids.     

Myelin Proteins in Reverse Micelles: Tight Lipid Association Required for Insertion of the Folch-Pi Proteolipid into a Membrane-Mimetic System

The solubility and reactivity of the Folch-Pi proteolipid from bovine CNS have been studied in reverse micelles of sodium bis(2-ethylhexyl)sulfosuccinate, isooctane, and water. Such a membrane-mimetic system resembles the aqueous spaces of the native myelin sheath in terms of its physicochemical properties. Although the proteolipid is completely insoluble in water, it can be inserted into the water-containing micellar system. In contrast, the lipid-depleted protein failed to be incorporated into these organized assemblies. The lipid requirements for insertion of the proteolipid were studied, therefore, after delipidation by several precipitations with isooctane, a nondenaturing solvent. Novel extraction procedures and quantitative analyses by HPLC of the protein-bound lipids revealed the persistence of a lipid-protein complex (6 +/- 1 mol of lipid/mol of protein) displaying optimal micellar solubilization. Competition experiments carried out with brain lipids provide evidence for a preference of the myelin protein for sulfatide, phosphatidylinositol, and phosphatidylserine, in that order. The resulting proteolipid, although differing in relative composition, showed good solubility in the membrane-mimetic system. In contrast, reconstitution experiments carried out with the lipid-depleted protein resulted in weak lipid binding and poor micellar incorporation. These results suggest that the tightly bound acidic lipids may stabilize a protein conformation required for insertion into the micellar system.