Evidence supporting the existence of a host cell surface receptor for Trypanosoma cruzi

Membrane fragments from trypomastigote forms of Trypanosoma cruzi inhibited the association of intact trypomastigotes with rat heart myoblasts whereas a similar preparation from non-invasive epimastigotes did not. Furthermore, killed trypomastigotes bound to the host cell surface and prevented the attachment of living organisms. Conversely, the extent of association of killed parasites with the host cells was reduced by the presence of living flagellates. These results suggest the presence of a distinct structure(s) on the surface of rat heart myoblasts to which infective forms of T. cruzi can bind.     

Characterization of Gypsy Moth (Lymantria dispar) Nuclear Polyhedrosis Virus

Characterization of the proteins and nucleic acid of the gypsy moth nuclear polyhedrosis virus isolated in Ithaca, N.Y. (LdNPV-IT) is presented. A total of 29 viral structural proteins were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis when the virus was isolated in the absence of alkaline protease activity. Fourteen surface envelope viral proteins were identified by lactoperoxidase iodination. Eleven proteins were associated with nucleocapsids prepared by Nonidet P-40 detergent treatment. Distinct alterations of viral proteins were documented when virions were purified in the presence of occlusion body-associated alkaline protease(s). Restriction enzyme digests of viral DNA indicated that this isolate was composed of a large number of genetic variants. On the basis of the major molar fragments resulting from EcoRI, BamHI, BglII, and HindIII digests, the molecular weight of the LdNPV genome was approximately 88 × 10⁶.     

Respiratory elastic load compensation in anesthetized patients with kyphoscoliosis

To evaluate the effects of abnormal respiratory mechanics and neuromuscular drive on the various components of elastic load compensation, we studied 16 anesthetized patients with kyphoscoliosis whose mean passive and active respiratory elastance (Ers and E'rs, respectively), active respiratory resistance, and peak inspiratory occlusion pressure were, respectively, 89, 84, 100, and 37% greater and inspiratory duration (TI) 13% less than corresponding values in 13 anesthetized controls. Ers comprised approximately 66% of effective elastance (E*rs) in both groups. E'rs, reflecting the role of the force-length properties of the active inspiratory muscles in increasing the internal impedance, comprised 83.8 and 86.1% of E*rs in the kyphoscoliosis patients and controls, respectively (P less than 0.001). This demonstrates the influence of increased intrinsic elastance and resistance and decreased TI on tidal volume defense in kyphoscoliosis patients in the absence of vagal modulation. In some patients the difference between Ers and E*rs was substantial, despite an unchanged or even shortened TI, suggesting that the Hering-Breuer reflex may affect stability through ways other than altering TI (e.g., via graded volume-dependent "terminal inhibition"). Characteristics of elastic load compensation in anesthetized kyphoscoliosis patients are similar to those of anesthetized normal subjects.     

Environment-dependent growth inhibition of human epidermal keratinocytes by recombinant human transforming growth factor-beta

Transforming growth factor-beta (TGF-beta) purified from platelets is a potent growth inhibitor of several normal epithelial cell types in culture. In contrast, some carcinoma cell lines derived from tumors of these same tissues are resistant to this factor. Using recombinant human TGF-beta, the authors have confirmed these results with six normal human epidermal keratinocyte strains and four human epidermal squamous carcinoma cell lines. However, the sensitivity of normal cells to TGF-beta was found to depend on the culture conditions. When grown in a specialized nutrient medium supplemented with pituitary extract, keratinocytes were completely inhibited by the addition of 0.3 ng/ml TGF-beta. In contrast, when their growth was supported by cocultivation with 3T3 fibroblast feeder cells, 30- to 100-fold higher concentrations of TGF-beta were required to achieve comparable growth inhibition. This differential sensitivity occurred despite the fact that in both culture systems TGF-beta in the culture medium had a half-life of about 50 minutes, becoming tightly bound to the surface of the culture dish. Bound TGF-beta proved to be biologically active and stable for about a week in the absence of 3T3 feeder cells. Incubating 3T3 cells on TGF-beta-coated dishes, however, resulted in nearly quantitative removal and degradation of the TGF-beta within 2 days, permitting normal rates of keratinocyte growth. The binding of TGF-beta to surfaces and the ability of fibroblasts to attenuate its inhibitory activity for epithelial cells must be considered when evaluating in vitro models and in planning strategies for the use of this factor in vivo.     

Dominant-negative mutants of platelet-derived growth factor revert the transformed phenotype of human astrocytoma cells.

Malignant astrocytoma is the most common primary human brain tumor. Most astrocytomas express a combination of platelet-derived growth factor (PDGF) and PDGF receptor which could close an autocrine loop. It is not known whether these autocrine loops contribute to the transformed phenotype of astrocytoma cells or are incidental to that phenotype. Here we show that dominant-negative mutants of the PDGF ligand break the autocrine loop and revert the phenotype of BALB/c 3T3 cells transformed by the PDGF-A or PDGF-B (c-sis) gene. Then, we show that these mutants are selective in that they do not alter the phenotype of 3T3 cells transformed by an activated Ha-ras or v-src gene or by simian virus 40. Finally, we show that these mutants revert the transformed phenotype of two independent human astrocytoma cell lines. They have no effect on the growth of human medulloblastoma, bladder carcinoma, or colon carcinoma cell lines. These observations are consistent with the view that PDGF autocrine loops contribute to the transformed phenotype of at least some human astrocytomas.     

Endogenous proteinases modulate the function of the β-adrenergic receptor-adenylate cyclase system

Photoaffinity labeling techniques have recently demonstrated that mammalian β₁- and β₂-adrenergic receptors reside on peptides of M_r 62 000–64 000. These receptor peptides are susceptible to endogenous metalloproteinases which produce peptides of M_r 30 000–55 000. Several proteinase inhibitors markedly attenuate this process, specifically EDTA and EGTA. In this study we investigated the functional significance of this proteolysis (and its inhibition) in the β₂-adrenergic receptor-adenylate cyclase system derived from rat lung membranes. Membrane preparations containing proteolytically derived fragments of the receptor of M_r 40000–55 000 are fully functional with respect to their ability to bind β-adrenergic antagonist radioligands such as [³H]dihydroalprenolol and β-adrenergic antagonist photoaffinity reagents such as p-azido-m-[^{125I]iodobenzylcarazolol}. They retain the ability to form a high-affinity, agonist-promoted, guanine nucleotide-sensitive complex thought to represent a ternary complex of agonist, receptor and guanine nucleotide regulatory protein. Nonetheless, after proteolysis, GTP is less able to revert this high-affinity receptor complex to one of lower affinity, and all aspects of adenylate cyclase stimulation are reduced. In addition, the functional integrity of the N protein in membranes prepared without proteinase inhibitors is reduced as assessed by reconstitution studies with the cyc[su− variant of S49 lymphoma cell membranes. These results suggest that endogenous proteolysis does not directly impair the ability of β-adrenergic receptors to either bind ligands or interact with the guanine nucleotide regulatory protein. However, they imply that endogenous proteolysis likely impairs the functionality of other components of the adenylate cyclase system, such as the nucleotide regulatory protein.     

Myocardial Revascularization in Patients 70 Years of Age and Older

Myocardial revascularization has been carried out by us in 67 patients 70 years of age or older. Advanced coronary artery disease was found at angiography in more than two thirds of the patients. The postoperative morbidity and mortality compare very favorably with those in younger patients. The early and late mortality in the 67 patients was 4.5 percent and 6.0 percent, respectively. Fifty-seven survivors have been followed an average of 21 months; for most patients there has been a pronounced improvement in clinical classification. Properly selected, patients of advanced age can undergo successful revascularization surgical procedures. The adequacy of function of the left ventricle, proper timing of the surgical operation and an aggressive yet realistic approach seem to be major determinants for a good result.     

Epitope mapping of snake venom phospholipases A2 with pseudexin monoclonal antibodies

Fifteen different monoclonal antibodies, developed against a pseudexin A, B, and C mixture, were screened for linear epitope recognition. Peptides (9-mers) spanning pseudexin B were synthesized on alanine-derivatized polyethylene pins and subsequently probed with antibody. Four antibodies recognized linear epitopes of pseudexin A, pseudexin B, and also nonidentical sequences found in other phospholipases A₂ (PLA₂s) as determined by enzyme-linked immunosorbent assays. Three antibodies recognized a highly conserved site important in calcium binding and the interlocking of dimeric forms of PLA₂. Antibodies neutralizing lethal or enzymatic effects of PLA₂ did not recognize linear epitopes.