Comparative histology of antelope placentomes

The histological structure of ruminant (family: Bovidae) placentomes in eight antelope species was compared to that of domestic cattle and sheep. The chorioallantoic villi differed in degree of branching, surface corrugation, and complexity of utero-placental junction. All species had the epitheliochorial type of placenta, with the epithelial lining of maternal caruncular crypts varying between cellular and syncytial types.     

Incomplete protection, but suppression of virus burden, elicited by subunit simian immunodeficiency virus vaccines.

We compared the efficacy of immunization with either simian immunodeficiency virus (SIV) Env glycoprotein (Env), Env plus Gag proteins (Gag-Env), or whole inactivated virus (WIV), with or without recombinant live vaccinia vector (VV) priming, in protecting 23 rhesus macaques (six vaccine and two control groups) from challenge with SIVmac251 clone BK28. Vaccination elicited high titers of syncytium-inhibiting and anti-Env (gp120/gp160) antibodies in all vaccinated macaques and anti-Gag (p27) antibodies in groups immunized with WIV or Gag-Env. Only WIV-immunized macaques developed anticell (HuT78) antibodies. After homologous low-dose intravenous virus challenge, we used frequency of virus isolation, provirus burden, and change in antibody titers to define four levels of resistance to SIV infection as follows. (i) No infection ("sterilizing" immunity) was induced only in WIV-immunized animals. (ii) Abortive infection (strong immunity) was defined when virus or provirus were detected early in the postchallenge period but not thereafter and no evidence of virus or provirus was detected in terminal tissues. This response was observed in two animals (one VV-Env and one Gag-Env). (iii) Suppression of infection (incomplete or partial immunity) described a gradient of virus suppression manifested by termination of viremia, declining postchallenge antibody titers, and low levels (composite mean = 9.1 copies per 10(6) cells) of provirus detectable in peripheral blood mononuclear cells or lymphoid tissues at termination (40 weeks postchallenge). This response occurred in the majority (8 of 12) of subunit-vaccinated animals. (iv) Active infection (no immunity) was characterized by persistent virus isolation from blood mononuclear cells, increasing viral antibody titers postchallenge, and high levels (composite mean = 198 copies per 10(6) cells) of provirus in terminal tissues and blood. Active infection developed in all controls and two of three VV-Gag-Env-immunized animals. The results of this study restate the protective effect of inactivated whole virus vaccines produced in heterologous cells but more importantly demonstrate that a gradient of suppression of challenge virus growth, reflecting partial resistance to SIV infection, is induced by subunit vaccination. The latter finding may be pertinent to studies with human immunodeficiency virus vaccines, in which it is plausible that vaccination may elicit significant suppression of virus infection and pathogenicity rather than sterilizing immunity.     

The purified myxoma virus gamma interferon receptor homolog M-T7 interacts with the heparin-binding domains of chemokines.

The myxoma virus T7 protein M-T7 is a functional soluble gamma interferon receptor homolog that has previously been shown to bind gamma interferon and inhibit its antiviral activities in a species-specific manner, but gene knockout analysis has suggested a further role for M-T7 in blocking leukocyte influx into infected lesions. We purified M-T7 to apparent homogeneity and showed that M-T7 is an N-linked glycoprotein that appears to be a stable homotrimer with a molecular mass of approximately 113 kDa in solution. M-T7, in addition to forming inhibitory complexes with rabbit gamma interferon, was also shown to bind to human interleukin-8, a prototypic member of the chemokine superfamily. Moreover, M-T7 was able to interact promiscuously with all members of the CXC, CC, and C chemokine subfamilies tested. Binding of human RANTES to M-T7 can be competed by rabbit gamma interferon and also by cold RANTES competitor with a 50% inhibitory concentration of 900 nM. Although M-T7 retains binding to a number of interleukin-8 N-terminal (ELR) deletion mutants, binding to mutants containing deletions in the C-terminal heparin-binding domain of interleukin-8 is abrogated. Furthermore, heparin effectively competes the interaction of M-T7 with the chemokine RANTES but not with rabbit gamma interferon. We propose that this novel M-T7 interaction with members of the chemokine superfamily may be facilitated through the conserved heparin-binding domains found in a wide spectrum of chemokines and that M-T7 may function by modulating chemokine-glycosaminoglycan interactions in virus-infected tissues.     

The relation of acyl transfer to the overall reaction of thiolase I from porcine heart

Thiolase I (long chain 3-ketoacyl-CoA-specific) from porcine heart has been characterized kinetically. In the direction of acetoacetyl-CoA cleavage, a variety of thiols including CoASH show the same Vmax at saturating concentrations of acetoacetyl-CoA. At a constant overall velocity of acetoacetyl-CoA disappearance, one of the two acetyl groups from acetoacetyl-CoA will partition between CoASH and 2-mercaptoethanol at increasing 2-mercaptoethanol concentrations. These observations suggest rate-determining formation of an acetyl enzyme intermediate in the direction of acetoacetyl-CoA cleavage. In the direction of acetoacetyl-CoA formation from two molecules of acetyl-CoA, the Vmax of acetoacetyl-CoA formation is identical with the Vmax for an acetyl-CoA in equilibrium CoA isotope exchange reaction and the Vmax for an enzyme-catalyzed acetyl transfer reaction between acetyl-CoA and 2-mercaptoethanol. This suggests that in the direction of acetoacetyl-CoA synthesis, the acetyl transfer half-reaction is rate-limiting. The acetyl intermediate has been isolated and characterized. The equilibrium constant for acetyl enzyme formation from acetyl-CoA and free enzyme is 1 +/- 0.5 X 10(-2). The rate constant for spontaneous hydrolysis of the acetyl enzyme (2.6 X 10(-4) s-1) is a factor of 400 faster than the rate constant for acetyl-CoA hydrolysis under comparable conditions. The acetyl enzyme is thermodynamically and kinetically destabilized compared to acetyl-CoA.     

Long-term maintenance of differentiated respiratory epithelium in organ culture I. Medium composition.

Six commerically prepared, chemically defined media were tested in the presence and absence of serum to assess their influence on the maintenance of viable hamster respiratory epithelium over extended periods of time in vitro. Unique proliferation of epithelial elements was observed in organ cultures maintained in "complex" media containing serum, whereas use of these media in the absence of serum produced disorganized epithelial changes resembling squamous metaplasia. Minimum essential media at low serum concentrations preserved the columnar structure of the normal tracheal epithelium for 8 wk and longer in vitro.     

B cells regulate murine gammaherpesvirus 68 latency

The dynamics of the establishment of, and reactivation from, gammaherpesviruses latency has not been quantitatively analyzed in the natural host. Gammaherpesvirus 68 (gammaHV68) is a murine gammaherpesvirus genetically related to primate gammaherpesviruses that establishes a latent infection in infected mice. We used limiting dilution reactivation (frequency of cells reactivating gammaHV68 in vitro) and limiting dilution PCR (frequency of cells carrying gammaHV68 genome) assays to compare gammaHV68 latency in normal (C57BL/6) and B-cell-deficient (MuMT) mice. After intraperitoneal (i.p.) inoculation, latent gammaHV68 was detected in the spleen, bone marrow, and peritoneal cells. Both B-cell-deficient and C57BL/6 mice established latent infection in peritoneal cells after either i.p. or intranasal (i.n.) inoculation. In contrast, establishment of splenic latency was less efficient in B-cell-deficient than in C57BL/6 mice after i.n. inoculation. Analysis of reactivation efficiency (reactivation frequency compared to frequency of cells carrying gammaHV68 genome) revealed that (i) regardless of route or mouse strain, splenic cells reactivated gammaHV68 less efficiently than peritoneal cells, (ii) the frequency of cells carrying gammaHV68 genome was generally comparable over the course of infection between C57BL/6 and B-cell-deficient mice, (iii) between 28 and 250 days after infection, cells from B-cell-deficient mice reactivated gammaHV68 10- to 100-fold more efficiently than cells from C57BL/6 mice, (iv) at 7 weeks postinfection, B-cell-deficient mice had more genome-positive peritoneal cells than C57BL/6 mice, and (v) mixing cells (ratio of 3 to 1) that reactivated inefficiently with cells that reactivated efficiently did not significantly decrease reactivation efficiency. Consistent with a failure to normally regulate chronic gammaHV68 infection, the majority of infected B-cell-deficient mice died between 100 and 200 days postinfection. We conclude that (i) B cells are not required for establishment of gammaHV68 latency, (ii) there are organ-specific differences in the efficiency of gammaHV68 reactivation, (iii) B cells play a crucial role in regulating reactivation of gammaHV68 from latency, and (iv) B cells are important for controlling chronic gammaHV68 infection.