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Biomedical subjects

W C Lai

Publications and source records attributed to W C Lai.

At least 19 recordsLinked to original sources
PubMed2003

Gigantic jets between a thundercloud and the ionosphere.

Transient luminous events in the atmosphere, such as lighting-induced sprites and upwardly discharging blue jets, were discovered recently in the region between thunderclouds and the ionosphere. In the conventional picture, the main components of Earth's global electric circuit include thunderstorms, the conducting ionosphere, the downward fair-weather currents and the conducting Earth. Thunderstorms serve as one of the generators that drive current upward from cloud tops to the ionosphere, where the electric potential is hundreds of kilovolts higher than Earth's surface. It has not been clear, however, whether all the important components of the global circuit have even been identified. Here we report observations of five gigantic jets that establish a direct link between a thundercloud (altitude approximately 16 km) and the ionosphere at 90 km elevation. Extremely-low-frequency radio waves in four events were detected, while no cloud-to-ground lightning was observed to trigger these events. Our result indicates that the extremely-low-frequency waves were generated by negative cloud-to-ionosphere discharges, which would reduce the electrical potential between ionosphere and ground. Therefore, the conventional picture of the global electric circuit needs to be modified to include the contributions of gigantic jets and possibly sprites.

Journal Article↗
PubMed2001

Murine cytomegalovirus is regulated by a discrete subset of natural killer cells reactive with monoclonal antibody to Ly49H.

Antiviral roles of natural killer (NK) cell subsets were examined in C57BL/6 mice infected with murine cytomegalovirus (MCMV) and other viruses, including lymphocytic choriomeningitis virus (LCMV), vaccinia virus (VV), and mouse hepatitis virus (MHV). Each virus vigorously induced an NK cell infiltrate into the peritoneal cavity and liver, causing some redistributions of NK cell subsets defined by monoclonal antibody (mAb) directed against Ly49A, C/I, D, and G2. Striking results were seen with a mAb (1F8) reactive with the positively signaling molecule Ly49H, present in MCMV-resistant C57BL/6 mice. mAb 1F8 also stains Ly49 C and I, but exclusion of those reactivities with mAb 5E6, which recognizes Ly49 C and I, indicated that Ly49H(+) cells infiltrated the peritoneal cavity and liver and were particularly effective at synthesizing interferon gamma. Depletion of 1F8(+) but not 5E6(+) cells in vivo by mAb injections enhanced MCMV titers by 20-1,000-fold in the spleen and approximately fivefold in the liver. Titers of LCMV or VV were not enhanced. These anti-MCMV effects were attributed to prototypical NK1.1(+)CD3(-) NK cells and not to NK1.1(+)CD3(+) "NK/T" cells. This is the first evidence that control of a virus infection in vivo is mediated by a distinct NK cell subset.

Amino Acid Sequence↗
PubMed2001

Monocyte membrane type 1-matrix metalloproteinase. Prostaglandin-dependent regulation and role in metalloproteinase-2 activation.

Membrane type 1-matrix metalloproteinase (MT1-MMP)-mediated activation of MMP-2 is thought to be important in the proteolysis of extracellular matrix in pathological events in which monocytes/macrophages are found. Here we report on the induction and regulation of human monocyte MT1-MMP and its role in MMP-2 activation. Activation of monocytes by lipopolysaccharide resulted in the induction of MT1-MMP mRNA and protein that was suppressed by inhibitors of prostaglandin synthesis (indomethacin), adenylyl cyclase (SQ 22536), and protein kinase A (Rp-cAMPs). Suppression of MT1-MMP by indomethacin and SQ 22536 was reversed by prostaglandin E(2) and dibutyryl cyclic AMP, respectively, demonstrating that induction of monocyte MT1-MMP is regulated through a prostaglandin-cAMP pathway. Functional analysis revealed that pro-MMP-2 in the supernatants from human bone marrow stromal fibroblasts, normal male-derived fibroblasts and melanoma cells (A2058) was converted to active MMP-2 when cultured with activated but not control monocytes. Antibodies against MT1-MMP blocked the activation of MMP-2. Tissue inhibitor of metalloproteinase-2 regulation of MMP-2 activation was shown through the addition of varying amounts of recombinant tissue inhibitor of metalloproteinase-2 with pro-MMP-2 to MT1-MMP-expressing monocytes. These findings demonstrate that activated monocytes express functionally active MT1-MMP that may play a significant role in the activation of MMP-2 produced by other cells and as such influence developmental and pathological conditions.

Adenine↗
PubMed2000

Ly49I NK cell receptor transgene inhibition of rejection of H2b mouse bone marrow transplants.

The Ly49 family of genes encode NK cell receptors that bind class I MHC Ags and transmit negative signals if the cytoplasmic domains have immunoregulatory tyrosine-based inhibitory motifs (ITIMs). 5E6 mAbs recognize Ly49C and Ly49I receptors and depletion of 5E6+ NK cells prevents rejection of allogeneic or parental-strain H2d bone marrow cell (BMC) grafts. To determine the function of the Ly49I gene in the rejection of BMC grafts, we transfected fertilized eggs of FVB mice with a vector containing DNA for B6 strain Ly49I (Ly49IB6). Ly49IB6 is ITIM+ and is recognized by 5E6 as well as Ly49I-specific 8H7 mAbs. Normal FVB H2q mice reject H2b but not H2d BMC allografts, and the rejection of H2b BMC was inhibited partially by anti-NK1.1 and completely by anti-asialo GM1, but not by anti-CD8, Abs. In FVB mice, NK1.1 is expressed on only 60% NK cells. FVB. Ly49IB6 hosts failed to reject H2d or H2b BMC, but did reject class I-deficient TAP-1-/- BMC, indicating that NK cells were functional. Nondepleting doses of anti-Ly49I Abs reversed the acceptance of H2b BMC by FVB.Ly49IB6 mice. FVB.Ly49IB6+/- mice were crossed and back-crossed with 129 mice-H2b, 5E6-, poor responders to H2d BMC grafts. While transgene-negative H2b/q F1 or first-generation back-crossed mice rejected H2b marrow grafts (hybrid resistance), transgene-positive mice did not. Thus B6 strain Ly49I receptors transmit inhibitory signals from H2b MHC class I molecules. Moreover, Ly49IB6 has no positive influence on the rejection of H2d allografts.

Animals↗
PubMed1999

Cutting edge: expression of functional CD94/NKG2A inhibitory receptors on fetal NK1.1+Ly-49- cells: a possible mechanism of tolerance during NK cell development.

Fetal liver- and thymus-derived NK1.1+ cells do not express known Ly-49 receptors. Despite the absence of Ly-49 inhibitory receptors, fetal and neonatal NK1.1+Ly-49- cells can distinguish between class Ihigh and class Ilow target cells, suggesting the existence of other class I-specific inhibitory receptors. We demonstrate that fetal NK1. 1+Ly-49- cell lysates contain CD94 protein and that a significant proportion of fetal NK cells are bound by Qa1b tetramers. Fetal and adult NK cells efficiently lyse lymphoblasts from Kb-/-Db-/- mice. Qa1b-specific peptides Qdm and HLA-CW4 leader peptide specifically inhibited the lysis of these blasts by adult and fetal NK cells. Qdm peptide also inhibited the lysis of Qa1b-transfected human 721.221 cells by fetal NK cells. Taken together, these results suggest that the CD94/NKG2A receptor complex is the major known inhibitory receptor for class I (Qa1b) molecules on developing fetal NK cells.

Aging↗
PubMed1998

DNA vaccines.

DNA vaccination against infectious diseases has created a new field of applied molecular immunology. cDNAs for 'protective' protein epitopes can be inserted into vectors containing strong mammalian promoters for high expression. Here we discuss the mechanisms of DNA vaccination and the successful and sometimes unsuccessful applications of DNA vaccination to protect animals against many different viral, bacterial mycoplasmal, protozoal, and worm infections or infestations. DNA immunization has been used to prevent or inhibit tumor development and to inhibit IgE responses by diverting the immune response from Th2 to Th1 helper cell dominance. Advantages and disadvantages of a variety of routes of administration and methods of immunization discussed include the use of the 'gene gun', the delivery of genes by aerosols, and deliberate induction of injury to muscles prior to injection of DNA to enhance gene expression. Vaccination performed using DNA without knowing beforehand the protective epitopes, using 'expression library immunization', is discussed. While this field is bound to expand rapidly for future clinical applications, we try to point out potential pitfalls as well as advantages of this relatively new technology.

Animals↗
PubMed1997

Therapeutic effect of DNA immunization of genetically susceptible mice infected with virulent Mycoplasma pulmonis.

Genetically susceptible BALB/c mice were immunized i.m. with DNA for one or two Mycoplasma pulmonis Ags (A7-1, A8-1) beginning either 1 wk before (vaccination) or 1 wk after (treatment) intranasal infection with 5 x 10(4) CFU virulent M. pulmonis organisms. Immunization of mice by this method induced both humoral and cellular immunity to M. pulmonis, largely prevented infection (vaccination), and cleared an ongoing pneumonia over time (treatment). Only one Ag gene was required. Thus, DNA immunization is a potential treatment for infections and may be useful in instances when drug therapy may not be available or effective.

Animals↗
PubMed1995

Protection against mycoplasma infection using expression-library immunization.

As is evident from the human immunodeficiency virus epidemic, there is no systematic method for producing a vaccine. Genetic immunization is a new approach to vaccine production that has many of the advantages of live/attenuated pathogens but no risk of infection. It involves introducing DNA encoding a pathogen protein into host cells and has shown promise in several disease models. Here we describe a new method for vaccine development, expression-library immunization, which makes use of the technique of genetic immunization and the fact that all the antigens of a pathogen are encoded in its DNA. An expression library of pathogen DNA is used to immunize a host thereby producing the effects of antigen presentation of a live vaccine without the risk. We show that even partial expression libraries made from the DNA of Mycoplasma pulmonis, a natural pathogen in rodents, provide protection against challenge from the pathogen. Expression library immunization may prove to be a general method for vaccination against any pathogen.

Animals↗
PubMed1995

Protection against Mycoplasma pulmonis infection by genetic vaccination.

The induction of an immune response against a foreign protein usually requires purification of that protein, which is injected into animals. The isolation of pure protein is time consuming and costly. Recently, a technique called biolistic transformation (biological ballistic system) microparticle injection, gene gun, or particle bombardment was developed. The basic idea is that DNA or biological material coated onto heavy tungsten or gold particles is shot into target cells or animals. We have vaccinated mice by introducing the gene (Mycoplasma pulmonis DNA or a specific fragment) encoding a protein recognized by a protective monoclonal antibody directly into the skin or muscle of mice by two methods: (i) using a hand-held form of the biolistic system that can propel DNA-coated gold microprojectiles (2 micrograms of DNA) directly into the skin; (ii) using a conventional intramuscular injection of the DNA (100 micrograms) into quadricep muscles of transfected mice. HeLa cells were transfected in vitro by the gene gun or by the liposomal delivery system. Indirect immuno-fluorescent antibody (IFA) assay of culture cells indicated that both methods could be successful. Production of antibody and cell-mediated immunity against M.pulmonis were monitored by assaying serum IFA and enzyme-linked immunosorbent assay (ELISA), and delayed type hypersensitivity. In addition, macrophage migration inhibition and lymphocyte transformation to antigen in spleen cells were also tested. Both delivery systems induced humoral and cellular immunity, and vaccinated the mice against infection. Genetic immunization by using the gene gun saves time, money, and labor; moreover, this general method is also applicable to gene therapy.

Animals↗
PubMed1994

Protection of mice against experimental murine mycoplasmosis by a Mycoplasma pulmonis immunogen in lysogenized Escherichia coli.

A construct of the Mycoplasma pulmonis (MP) genomic library, using randomly sheared DNA, was cloned in lambda gt11 and transfected into C600 Escherichia coli organisms. Clones of E. coli expressing a fusion protein reactive with anti-MP and monospecific serum were transferred orally or intravenously into Balb/c mice. Expression of the fusion protein was induced by adding isopropyl-beta-D-thiogalactopyranoside to the drinking water. This vaccination protocol led to local and systemic antibody formation, to generation of immune lymphocytes and to protection against large numbers of virulent MP organisms. This approach might be generally successful in preventing infectious disease.

Administration, Oral↗
PubMed1994

Mycoplasma pulmonis 46-kDa trypsin-resistant protein adheres to rat tracheal epithelial cells.

Results of competitive binding studies with radiolabeled and unlabeled Mycoplasma pulmonis and rat tracheal explant cultures indicated no effect of trypsin treatment on the ability of M. pulmonis to bind to explants. A trypsin-resistant 46-kDa membrane protein, which binds isolated rat tracheal epithelial cells in culture, was purified and used to produce specific antibodies that block adhesion of mycoplasmas to tracheal explants. These results suggest that M. pulmonis adheres to rat tracheal epithelium via a trypsin-resistant 46-kDa protein.

Animals↗
PubMed1993

Genetic control of resistance to Mycoplasma pulmonis infection in mice.

The differences in susceptibility of various inbred strains of mice to a highly pathogenic strain of Mycoplasma pulmonis CT (T2) has been known for some time. We assessed the genetic control of resistance to T2 infection. Tracheolung lavage samples and lungs of mice were assessed for T2 organisms after intratracheal injection of T2. We found that H-2b (C57BL/6 (B6) and H-2k B10.BR mice were resistant, whereas H-2b A.By, H-2k C3H/Bi, H-2k C3H/HeJ (C3H), and H-2b BALB.B mice were susceptible. We also typed individual B6C3F2 mice for H-2 and for resistance to T2 and observed that resistance to T2 infections is controlled by a single dominant gene not linked to H-2. Histologic examination revealed severe lung lesions typical of M. pulmonis infections in susceptible C3H mice, in contrast to minimal lung lesions in resistant B6 mice. No significant titers of local or systemic antimycoplasma antibodies were detected in either resistant or susceptible mice at 5 days postinfection. Macrophages taken from uninfected B6 or C3H mice failed to inhibit growth of T2 in vitro. However, macrophages from B6 mice did inhibit growth of T2 much better than C3H macrophages when harvested on day 5 of infection. Thus, there is an association between activation of macrophage bactericidal function and genetic resistance to growth of T2 organisms.

Animals↗
PubMed1991

Potential subunit vaccine against Mycoplasma pulmonis purified by a protective monoclonal antibody.

Monoclonal antibodies (mAbs) were produced against Mycoplasma pulmonis (MP); some were highly protective in the treatment of experimental infections of BALB/c mice. The mAbs inhibited MP growth in vitro and prevented the attachment of MP to fibroblasts or to red blood cells. Three separate mAbs recognized 54-76% of 54 clinical isolates of MP, and the three together detected all 54 isolates. We used the mAbs to purify the antigens by affinity column chromatography. The purified antigen used to vaccinate mice and to immunize rabbits produced antibodies capable of significant growth inhibition in sera and tracheolung lavage fluids. The vaccinated mice were challenged with various doses of a highly virulent T2 strain of MP. Assays for viable MP organisms and for histopathological changes in the lungs of infected mice indicated that mice were protected if the challenge dose was 10(3)-10(5), but not 10(7), c.f.u. The sera of immunized rabbits were used to passively transfer immunity to mice. The sera provided complete protection against 1 x 10(6) c.f.u. T2 MP. We conclude that MP antigens purified by this protocol can provide a safe vaccine against this disease, at least in mice.

Animals↗
PubMed1991

A monoclonal antibody against a Pasteurella multocida outer membrane protein protects rabbits and mice against pasteurellosis.

Monoclonal antibodies (MAbs) directed against the 37.5-kDa outer membrane protein were produced by fusing myeloma cells with spleen cells obtained from mice immunized with a pathogenic strain of Pasteurella multocida isolated from a rabbit. Desirable MAbs were selected by enzyme-linked immunosorbent assay, whole-cell radioimmunoprecipitation (WC-RIP), and Western blot (immunoblot) analysis. WC-RIP and Western blot analyses, using MAb 1608 adsorbed with intact P. multocida cells and the eluted MAb, demonstrated that the antigen recognized by this MAb is exposed on the cell surface, is antibody accessible, and has an estimated molecular mass of 37.5 kDa. Treatment of outer membrane vesicles of P. multocida with proteinase K totally abrogated the MAb 1608 activity, indicating that this MAb binds to a protein antigenic determinant. Furthermore, MAb 1608 was nonreactive to purified lipopolysaccharide in Western blot analysis. Passive transfer studies showed that nine rabbits inoculated intranasally with MAb 1608 and homologously challenged intranasally had significantly reduced mortality, severity of pneumonia, prevalence of P. multocida colonization in nonrespiratory organs, and numbers of P. multocida in nasal cavities compared with the controls. Furthermore, the number of P. multocida in lungs was reduced 84,750-fold. Similarly, passive transfer experiments indicated that MAb 1608 protected mice against homologous and heterologous challenges with P. multocida strains bearing the antigenic determinant recognized by MAb 1608. However, no protection was afforded by MAb 1608 when mice were challenged with a P. multocida strain lacking the antigenic determinant recognized by MAb 1608. This study establishes that the 37.5-kDa outer membrane protein is the target for a protective MAb.

Animals↗
PubMed1991

Vaccination of Lewis rats with temperature-sensitive mutants of Mycoplasma pulmonis: adoptive transfer of immunity by spleen cells but not by sera.

Temperature-sensitive mutant vaccines protect rats against Mycoplasma pulmonis infection. The role of the humoral or cellular immune response in resistance to mycoplasma infection was investigated by adoptive-transfer experiments. Spleen cells from Lewis rats vaccinated but not challenged with wild-type organisms (vaccinated) and spleen cells from rats vaccinated (or not) and challenged were effective in preventing syngeneic recipients from developing respiratory disease. There was also a significant reduction in the incidence and number of challenging organisms in the respiratory system. In contrast, sera from the same donors had no detectable effect on the number of mycoplasmas recovered or on lesion development in the respiratory tract. We conclude that cellular immunity rather than humoral immunity generated in vaccinated rats confers protection against subsequent infection.

Animals↗