Effects of exogenous, nonleukemogenic, ecotropic murine leukemia virus infections on the immune systems of adult C57BL/6 mice.

Mouse AIDS (MAIDS) develops in mice infected with a mixture of replication-competent ecotropic and mink lung cell focus-inducing murine leukemia viruses and an etiologic replication-defective virus. Helper viruses are not required for induction of MAIDS, but the time course of disease is accelerated in their presence. To understand the possible contributions of ectropic murine leukemia viruses to MAIDS pathogenesis, we biologically cloned a series of viruses from the MAIDS-inducing LP-BM5 virus mixture.

In vivo treatment with interleukin 12 protects mice from immune abnormalities observed during murine acquired immunodeficiency syndrome (MAIDS).

Lymphoproliferation, chronic B cell activation resulting in hypergammaglobulinemia, and profound immunodeficiency are prominent features of a retrovirus-induced syndrome designated murine acquired immunodeficiency syndrome (MAIDS). In vivo treatment of infected mice with recombinant interleukin 12 (IL-12) beginning at the time of infection or up to 9 wk after virus inoculation markedly inhibited the development of splenomegaly and lymphadenopathy, as well as B cell activation and Ig secretion. Treatment with IL-12 also had major effects in preventing induction of several immune defects including impaired production of interferon gamma (IFN-gamma) and IL-2 and depressed proliferative responses to various stimuli.

Murine AIDS is an antigen-driven disease: requirements for major histocompatibility complex class II expression and CD4+ T cells.

Murine AIDS (MAIDS) is a complex syndrome of lymphoproliferation and immunodeficiency induced by a replication-defective murine leukemia virus (BM5def) that encodes Pr60gag as its only product. It has been suggested that the gag polyprotein is responsible for vigorous antigenic stimulation of CD4+ T cells and generalized secondary activation of the immune system. This model was tested first by infecting mice (C2K/O) that lack class II major histocompatibility complex molecules required for presentation of antigens to CD4+ T cells.

Enhanced pulmonary histopathology induced by respiratory syncytial virus (RSV) challenge of formalin-inactivated RSV-immunized BALB/c mice is abrogated by depletion of interleukin-4 (IL-4) and IL-10.

In previous studies, children immunized with a formalin-inactivated respiratory syncytial virus vaccine (FI-RSV) developed severe pulmonary disease with greater frequency than did controls during subsequent natural RSV infection. In earlier efforts to develop an animal model for this phenomenon, extensive pulmonary histopathology developed in FI-RSV-immunized cotton rats and mice subsequently challenged with RSV. In mice, depletion of CD4+ T cells at the time of RSV challenge completely abrogated this histopathology.

Mechanism of platelet-derived growth factor (PDGF) AA, AB, and BB binding to alpha and beta PDGF receptor.

The biological effects of platelet-derived growth factor (PDGF) are mediated by cell surface alpha and beta PDGF receptors, which, as a result of ligand binding, undergo dimerization in a manner consistent with PDGF being bivalent. In order to directly demonstrate PDGF bivalency and to define the binding of PDGF AB to isolated beta receptor, we developed solid-phase binding assays using purified recombinant extracellular domain of human PDGF receptors. PDGF AA, AB, and BB were prepared from the monomeric chains expressed in Escherichia coli, and each was purified to homogeneity; PDGF AB contained < 0.

Five PDGF B amino acid substitutions convert PDGF A to a PDGF B-like transforming molecule.

We used site-directed mutagenesis to determine the minimum number of PDGF B residues needed to convert PDGF A to a potently transforming PDGF B-like molecule. Substitution of two PDGF B subdomains, 106-115 and 135-144, were found to be critical. These substitutions were sufficient to broaden the ability of PDGF A to activate beta as well as alpha platelet-derived growth factor (PDGF) receptors and increase its transforming efficiency to that of PDGF B.

A small v-sis/platelet-derived growth factor (PDGF) B-protein domain in which subtle conformational changes abrogate PDGF receptor interaction and transforming activity.

Deletion scanning mutagenesis within the transforming region of the v-sis oncogene was used to dissect structure-function relationships. Mutations affecting codons within a domain encoding amino acids 136 through 148 had no effect upon homodimer formation or recognition by antisera which detect determinants dependent upon native intrachain disulfide linkages, yet the same mutations completely abolished transforming activity. A platelet-derived growth factor B (PDGF B) monoclonal antibody that prevents its interaction with PDGF receptors recognized v-sis, delta 142 (deletion of codon 142), and delta 148 but not delta 136, delta 137, or delta 139 mutants.

Molecular localization of the transforming and secretory properties of PDGF A and PDGF B.

Human platelet-derived growth factor (PDGF) is a connective tissue cell mitogen comprised of two related chains encoded by distinct genes. The B chain is the homolog of the v-sis oncogene product. Properties that distinguish these ligands include greater transforming potency of the B chain and more efficient secretion of the A chain.

Chimeric molecules map and dissociate the potent transforming and secretory properties of PDGF A and PDGF B.

Human platelet-derived growth factor (PDGF) is a connective tissue cell mitogen comprising two related chains encoded by distinct genes. The B chain is the homolog of the v-sis oncogene product. Properties that distinguish these ligands include greater transforming potency of the B chain and more efficient secretion of the A chain.

Expression and purification of biologically active v-sis/platelet-derived growth factor B protein by using a baculovirus vector system.

Malignant transformation induced by simian sarcoma virus is mediated by its v-sis protein, the monkey homolog of the platelet-derived growth factor (PDGF) B chain. By use of an appropriately engineered baculovirus expression vector, the v-sis protein was expressed in the insect cell line Spodoptera frugiperda (Sf9) at a level 50- to 100-fold higher than that observed with overexpression in mammalian-cell transfectants. The sis protein produced by Sf9 cells underwent processing similar to that observed in mammalian cells, including efficient disulfide-linked dimer formation.

The role of individual cysteine residues in the structure and function of the v-sis gene product.

The v-sis oncogene encodes a platelet-derived growth factor (PDGF)-related product whose transforming activity is mediated by its functional interaction with the PDGF receptor. PDGF, as well as processed forms of the v-sis gene product, is a disulfide-linked dimer with eight conserved cysteine residues in the minimum region necessary for biologic activity. Site-directed mutagenesis of the v-sis gene revealed that each conserved cysteine residue was required directly or indirectly for disulfide-linked dimer formation.

In vitro mutagenesis of the v-sis transforming gene defines functional domains of its growth factor-related product.

The polypeptide sequence of the v-sis transforming gene product of simian sarcoma virus (SSV) can be divided into four regions that are likely to represent structural domains of the protein. Mutations were generated in the SSV nucleotide sequence to assay the extent or function of each of these regions. The results indicate that the helper virus-derived amino-terminal sequence as well as a core region homologous to polypeptide chain 2 of platelet-derived growth factor (PDGF) are required for the transforming function of the protein.

Inhibition by retinoic acid of murine retrovirus-induced cellular transformation and tumor formation.

The effect of all-trans-retinoic acid (RA) on cellular transformation and on tumorigenicity of retrovirally transformed cells was investigated. RA treatment of NRK and NIH/3T3 cells transformed by BALB/c murine sarcoma virus (MuSV), Kirsten murine sarcoma virus (K-MuSV), and simian sarcoma virus resulted in a significant reduction in anchorage-dependent growth of only K-MuSV-transformed NRK cells. A 62% reduction in cell number was observed at 10(-5) M RA.