The effects of thalidomide treatment on autoimmune-prone NZB and MRL mice are consistent with stimulation of the central immune system

We describe here some immunomodulatory effects of thalidomide on autoimmune-prone mice. The highly increased synthesis of splenic IgM in NZB mice, of splenic and lymph node IgG of different subclasses in MRL/n mice, and of splenic and lymph node IgG1 in MRL/lpr mice was markedly inhibited by thalidomide treatment. After a single treatment with 3 mg of thalidomide, the following changes were observed in NZB mice: (i) an initial decrease in the numbers of large CD5+ microhigh, and in the numbers of total CD5+ micro-, CD5- microhigh, CD5+ microhigh lymphocyte populations of the pleural cavity followed by a late increase in the numbers of large cells of the three cell populations; (ii) a consistent increase in the numbers of a CD5low microlow pleural lymphoid population; (iii) a consistent reduction in the numbers of splenic large CD5+ B cells and an oscillatory increase in the number of cells with CD5- phenotype; (iv) a late reduction in the numbers of splenic total CD5+ B cells. These results are consistent with the notion that thalidomide controls a disease-associated expansion of B cells in autoimmune prone mouse strains through a stimulatory effect of the drug on the immune system.

Structure of ribonuclease A derivative II at 2.1-A resolution

The crystal structure of bovine pancreatic ribonuclease A derivative II, a covalent derivative obtained by reaction of 6-chloropurine 9-beta-D-ribofuranosyl 5'-monophosphate with the alpha-amino group of Lys-1, has been determined and refined at 2.1-A resolution with an agreement factor R = 0.166 for 6254 reflections in the resolution shell 8.0 to 2.1 A. Crystals are orthorhombic and belong to space group C222(1) with unit cell parameters a = 75.73 A, b = 57.85 A, and c = 53.26 A. This crystal packing had never been reported before for pancreatic ribonuclease nor its complexes. The structure found is in accordance with the location of p2, B3, and R3 subsites at the N-terminal region of the protein and provides an explanation of the catalytic behavior observed for this derivative. In particular, differences in kinetic parameters and in the pKa value of His-119 between derivative II and native ribonuclease A can be interpreted on the basis of the position of the phosphate moiety within the derivative structure. Some uncertainty remains on the nucleotide sugar conformation determined.

Activation of human neutrophils by phorbol ester decreases the cytoplasm compactness and the lactoferrin content of the granulocytes

Human neutrophils isolated from the blood were incubated in vitro for 30 min with 25 ng/ml of phorbol 12-myristate 13-acetate (PMA), a protein kinase C activator, to study its effect on the fine structure of granulocytes and on the subcellular distribution of lactoferrin (Lf). Flow cytometry analysis of the human neutrophils showed that PMA induced a decrease in size and granularity of the cells. By electron microscopy, the PMA-treated cells showed numerous empty vesicles, smoothing of the cell surface, and a marked decrease in the compactness of the cytoplasmic ground substance. High-resolution immunogold ultracytochemistry showed that neutrophils lost most of their content in Lf after the PMA incubation. In thin sections, the cytoplasmic compartment of PMA-treated neutrophils contained an average of 1.03 +/- 0.3 Lf-positive vesicles per microns 2, whereas control granulocytes showed an average of 5.72 +/- 1.49 Lf vesicles per microns 2 of cytoplasm. Most of PMA-treated neutrophils kept some Lf-positive vesicles; a significant minority (10-15%) of the granulocytes showed cytological features of cell death. We conclude that the PMA-induced neutrophil activation is associated with microanatomical changes that include i) exocytosis of most, but not all, of the Lf-bearing vesicles; ii) rounding up of the cell outline; and iii) decrease in the compactness of the cytoplasmic ground substance.

Role of B and T lymphocytes in the specific immunosuppression induced by a protein released by porcine monocytes infected with African swine fever virus

Some immunobiological aspects of host responses to an immunosuppressive protein (p36) released by porcine monocytes upon infection with African swine fever virus were analysed in a murine system. Treatment of normal, adult C57BL/6 mice with p36 (i) significantly delayed allogenic skin graft rejection; (ii) suppressed the specific plaque-forming cell response to immunization with heterologous erythrocytes; but (iii) induced marked increases in the numbers of 'background' splenic Ig-secreting plaque-forming cells. Cytofluorometric analysis of spleen cells revealed that a considerable fraction of all B cells, as well as CD4 and CD8 T lymphocytes, undergo blast transformation after p36 treatment. The immunosuppressive effects do not seem to result from 'antigenic competition', for they cannot be induced by even higher doses of pig albumin or by culture products of non-infected pig monocytes. Suppression of specific antibody responses and stimulation of 'background' plaque-forming cells are both T cell-dependent, since they are markedly reduced in thymectomized mice and in animals treated with anti-CD4 or anti-CD8 antibodies. This suggests the relationship between non-specific stimulation and specific suppression of 'unrelated' immune responses and reinforces the notion that viral-associated immunosuppression may be due to overstimulation. The present murine experimental model may prove valuable in the study of immunosuppression associated with infection, even for microorganisms which do not infect mice.

1H-n.m.r. studies of the isolated activation segment from pig procarboxypeptidase A

The isolated activation segment (asA) from pig pancreatic procarboxypeptidase A was studied by 1H-n.m.r. spectroscopy over a wide range of solution conditions. Isolated asA shows many characteristics of compactly folded globular proteins, such as the observation of perturbed positions for resonances from methyl groups, alpha-carbon atoms, histidine residues and the tyrosine residue. The single tyrosine residue (Tyr-70) exhibits a very high pKa, and both histidine and tyrosine residues show slow chemical modification (deuteration and iodination). In contrast, asA shows rapid NH exchange. Analysis of the spectra by pH titration and nuclear Overhauser effects revealed several residue interactions. Quantitative analysis of deuterium and tritium exchange allowed the assignment of the histidine C-2-H resonances to their respective residues in the sequence. His-66, the closest to the sites of proteolytic attack in the proenzyme, is shown to be the most accessible to solvent in procarboxypeptidase A. It was also shown that asA is thermally very stable ['melting' temperature (Tm) 88 degrees C] and requires a high urea concentration for denaturation (6.25 M, at pH 7.5). Evidence is presented for some degree of conformational flexibility in the premelting range, a feature that could be ascribed to the preponderance of helical secondary structure and to the lack of disulphide bridges. The free solution structure of asA is probably unchanged when it binds to carboxypeptidase A.

Correlation between B-cell mitogenicity and immunosuppressor effects of a protein released by porcine monocytes infected with African swine fever virus

Virus-free supernatants of cultured swine monocytes infected by African swine fever virus (ASFV) suppressed in vitro proliferation of porcine and human blood mononuclear cells in response to phytohemagglutinin and the in vivo primary immune response of C57BL/6 mice against sheep RBC. The supernatants were fractionated by discontinuous ion-exchange chromatography and subfractionated by double-step preparative isoelectric focusing. The pool of the most purified active subfractions (F5'EP-ASFV) is made up of heat-unstable material, can be stained by silver nitrate, and has an isoelectric point of 3.88, a maximal optical density at 280 nm, and a mass of 36,000 daltons. In vivo kinetic studies in nonimmunized C57BL/6 mice were performed on days 1, 2, 3, 5, and 7 after injection with 50 micrograms of F5'EP-ASFV protein. Compared with the untreated mice, the treated mice had a noticeable increase in nonspecific immunoglobulin-secreting splenic plaque-forming cells (PFC) with the following isotype profile: IgG2a greater than IgG2b greater than IgG3 greater than IgG1 congruent to IgM. Three days after treatment with the active material, specific IgM PFC against sheep RBC increased up to 23-fold. In C57BL/6 mice immunized against sheep RBC 2 days after treatment with F5'EP-ASFV, the increase in nonspecific PFC was followed by a suppression of specific PFC response in the respective isotype. When C57BL/6 mice were treated after priming with sheep RBC, however, there was little or no suppression of specific PFC and the increase in nonspecific PFC was considerably lower than that in the other F5'EP-ASFV-treated mice. In this case, kinetic curves of specific vs nonspecific PFC of each isotype were mirror images. Mice treated with 200 micrograms of F5'EP-ASFV protein died with hemorrhagic diastasis.

Analysis of the thermal unfolding of porcine procarboxypeptidase A and its functional pieces by differential scanning calorimetry

Porcine pancreatic procarboxypeptidase A and its tryptic peptides, carboxypeptidase A and the activation segment, have been studied by high-sensitivity differential scanning calorimetry (DSC). The thermal denaturation of the zymogen and the active enzyme has been carried out at two pH values, 7.5 and 9.0, at different ionic strengths and at different scan rates. The endothermic transitions for these two proteins were always irreversible under all conditions investigated. The denaturation behaviour of both proteins seems to fit very well with the kinetic model for the DSC study of irreversible unfolding of proteins recently proposed by one of our groups. From this model, the activation energies obtained for the denaturation of the pro- and carboxypeptidase were 300 +/- 20 kJ mol-1 and 250 +/- 14 kJ mol-1 respectively. On the other hand, the isolated activation segment appears as a thermostable piece with a highly reversible thermal unfolding which follows a two-state process. The denaturation temperature observed for the isolated segment was always at least 15 K higher than those of the zymogen and the active enzyme.

Analysis of the conformation and ligand-binding properties of the activation segment of pig procarboxypeptidase A

The isolated activation segment of pig procarboxypeptidase A binds two Tb3+ ions in a strong and specific way. In contrast, the binding of Ca2+, Cd2+ and Mg2+ is weak. The binding of Tb3+ increases the resistance of the isolated activation segment against proteolysis and competes for the binding of the carbocyanine dye Stains-All. This dye forms complexes with the activation segment showing spectral properties similar to those observed with EF-hand structures. The presented results support a previous hypothesis on the existence of two regions in the activation segment of pancreatic procarboxypeptidases structurally related to Ca2+-binding domains of the EF-hand protein family.

Conformational predictive studies on the activation segment of pancreatic procarboxypeptidases

Little is known about the conformation and evolutionary origin of the activation segment of pancreatic procarboxypeptidases. Analysis of the sequence and secondary structure propensities of these propeptide segments indicate that they contain two regions structurally related to the Ca2+-binding sites of the EF-hand protein family. This proposed homology could explain how (and why) carboxypeptidases developed such long (94 residues) activation peptides.

Urea-gradient gel electrophoresis studies on the association of procarboxypeptidases A and B, proproteinase E, and their tryptic activation products

Monomeric procarboxypeptidase A (PCPA) and isolated proproteinase E (PPE), both from pig pancreas, were shown by means of electrophoresis on transverse urea gradients (0-9 M) to form a very stable complex, identical to their natural binary complex. Although the complex is maintained by the interaction of both active regions, the activation segment of PCPA participates directly in the binding. Procarboxypeptidase B (PCPB) also associates with PPE, but in this case the complex shows low stability. In contrast with carboxypeptidases A that strongly bind to their corresponding severed activation segments, no interaction was observed between carboxypeptidase B and its severed activation segment. The above results give some insight into several characteristics of the structure and activation properties of pancreatic PCPA and PCPB.

Preparative isolation of the two forms of pig pancreatic pro-(carboxypeptidase A) and their monomeric carboxypeptidases A

A method is reported for the preparative isolation of the two forms of pro-(carboxypeptidase A) from pig pancreas: the monomer and the binary complex with pro-(proteinase E). This method, which is mainly based on chromatography on DEAE-Sepharose at pH 5.7, allows these proenzymes to be prepared more quickly and in safer conditions than with other reported methods. Undegraded and homogeneous carboxypeptidase A1 and A2 species (peptidyl-L-amino acid hydrolase, EC 3.4.17.1), in monomeric forms with high specific activity, are also obtained in high yield by controlled trypsin activation of either of the pro-(carboxypeptidases A) followed by chromatography on DEAE-Sepharose at pH 5.8 under dissociating conditions (7 M-urea).

The activation segment of procarboxypeptidase A from porcine pancreas constitutes a folded structural domain

The controlled action of trypsin on porcine pancreatic procarboxypeptidase A releases a large activation peptide which contains the activation segment of the proenzyme. Circular dichroism studies indicate that the isolated activation peptide contains a high percentage of residues in ordered secondary structures (mainly alpha-helix). This result agrees with predictions of secondary structure carried out on the published amino acid sequence of the homologous rat proenzyme. Moreover, proton magnetic resonance spectroscopy shows that the peptide adopts a thermostable tertiary structure with characteristics typical of globular proteins. The results as a whole indicate that the activation segment of porcine pancreatic procarboxypeptidase A constitutes a folded structural domain.

The severed activation segment of porcine pancreatic procarboxypeptidase A is a powerful inhibitor of the active enzyme. Isolation and characterisation of the activation peptide

The activation peptide of the monomeric procarboxypeptidase A from porcine pancreas was isolated by means of controlled trypsin digestion of the proenzyme followed by ion-exchange chromatography under dissociating conditions (7 M urea). The molecular weight of the isolated peptide was estimated to be around 11500-12000 (corresponding to approx. 100-103 residues) as judged by SDS electrophoresis and amino acid analysis, a figure that agrees with the differences between the corresponding values for procarboxypeptidase A and carboxypeptidase A (peptidyl-L-amino acid hydrolase, EC 3.4.17.1). The activation peptide has a high content of hydrophobic and acidic amino acids, and lacks cysteine. A remarkable feature is the strong competitive inhibitory action of the peptide on both porcine and bovine pancreatic carboxypeptidase A activity, with a Ki in the nanomolar range, and its null ability to inhibit porcine pancreatic carboxypeptidase B (EC 3.4.17.2). The above properties, and the fact that the peptide has the same N-terminal residue (lysine) as the parent procarboxypeptidase A, suggest that the isolated peptide contains most (if not all) of the activation segment of the proenzyme.