Interferon-gamma-activated human monocytes inhibit the intracellular multiplication of Legionella pneumophila

We have examined the interaction between interferon-gamma (IFN-gamma)-activated human monocytes and Legionella pneumophila, the agent of Legionnaires' disease. Human monocytes activated with human recombinant IFN-gamma inhibit the intracellular multiplication of L. pneumophila. The degree of inhibition is proportional to the concentration of IFN-gamma, and maximal inhibition consistently occurs with greater than or equal to 2 micrograms/ml. Monoclonal anti-IFN-gamma antibody completely neutralizes the capacity of IFN-gamma to activate monocytes. Monocytes infected 24 hr after explantation maximally inhibit L. pneumophila multiplication if treated with IFN-gamma before infection or up to 2 hr after infection; treatment 6 hr or more after infection results in submaximal inhibition. Monocytes infected 48 hr after explantation inhibit L. pneumophila multiplication maximally if treated with IFN-gamma up to 12 hr before infection, but submaximally if treated at the time of infection. Once activated, monocytes inhibit L. pneumophila multiplication in the absence of IFN-gamma in the culture. Strikingly, monocytes maximally inhibit L. pneumophila multiplication after treatment with IFN-gamma for as briefly as 1 hr before infection. In the absence of anti-L. pneumophila antibody, neither IFN-gamma-activated monocytes nor nonactivated monocytes kill L. pneumophila. In the presence of specific antibody and complement, IFN-gamma-activated monocytes kill a proportion (0.5 log) of an inoculum but not more than nonactivated monocytes. L. pneumophila forms a specialized phagosome in IFN-gamma-activated monocytes that does not differ ultrastructurally from the L. pneumophila phagosome in nonactivated monocytes. These results demonstrate that IFN-gamma can activate human monocytes to exert a potent antimicrobial effect against a highly virulent intracellular bacterial pathogen. These findings extend previous observations on interactions between activated mononuclear phagocytes and L. pneumophila, and additionally support the hypothesis that cell-mediated immunity plays a major role in host defense against L. pneumophila.     

Effect of Water Stress on Photochemical Activity of Chloroplasts during Greening of Etiolated Barley Seedlings

Water stress retards accumulation of chlorophyll and chlorophylla/b protein complex during greening of barley seedlings in light.The rate of 2,6-dichlorophenol indophenol (DCPIP) photoreductionin isolated chloroplast which decreases under water stress isenhanced significantly in the presence of electron donors, diphenylcarbazide (DPQ) and Mn²⁺. Under water stress, the decrease ofthe rate of oxygen evolution measured in continuous white lightwas 40–73% and that of oxygen uptake (as a measure ofelectron transport through PS I from reduced DCPIP) was onlyabout 20%. During greening, under water stress, (i) a differentialinhibition of PS II biosynthesis as compared to PS I occurs,(ii) the site of electron donation by DPC seems to be closerto the reaction center ofPS II, (iii) the oxidizing side ofPS II near the oxygen-evolving system is affected maximallyby water stress. (Received March 11, 1980; Accepted November 13, 1980)     

Biology of vascular endothelial growth factors

Angiogenesis is the process by which new blood vessels are formed from existing vessels. The vascular endothelial growth factors (VEGFs) are considered as key molecules in the process of angiogenesis. The VEGF family currently includes VEGF-A, -B, -C, -D, -E, -F and placenta growth factor (PlGF), that bind in a distinct pattern to three structurally related receptor tyrosine kinases, denoted VEGF receptor-1, -2, and -3. VEGF-C and VEGF-D also play a crucial role in the process of lymphangiogenesis. Here, we review the biology of VEGFs and evaluate their role in pathological angiogenesis and lymphangiogenesis.     

Response to complete and skeleton photoperiods in subtropical male house sparrow, Passer domesticus (Linnaeus)

To examine the importance of the inductive light period of a skeleton photoperiod in relation to the endogenous circadian rhythm of photoinducibility mediating photoperiodic induction, P. domesticus were exposed for 28 weeks to a series of skeleton photoperiods, viz. 6L:4D:1L:13D, 6L:6D:1L:11D. 6L:8D:1L:9D and 6L:14D:1L:3D. The inductive effects of 1 hr light pulse at night varied depending on the time of its placement. To compare the inductive effects of complete and its corresponding skeleton photoperiods, birds in the second experiment were subjected for 20 weeks to 12L:12D and 6L:5D:1L:12D given daily or interposed on alternate days with constant darkness (12L:12D/DD and 6L:5D:1L:12D/DD). There was a difference in the rate and magnitude of response between the complete and skeleton photoperiods. It appears that the subtropical house sparrow uses photoperiodic strategy in regulation of its seasonal testicular responses similar to that is reported for its temperate population.     

Vaccination with a novel recombinant Leishmania antigen plus MPL provides partial protection against L. donovani challenge in experimental model of visceral leishmaniasis

The acquisition of immunity following subclinical or resolved infection with the intracellular parasite Leishmania donovani suggests that vaccination could prevent visceral leishmaniasis. The characteristics and in vitro stimulating capability of the recombinant proteins expressed by previously identified clones on the basis of their capacity to stimulate an indigenously established Leishmania-specific cell line leading to high level of IFN-γ suggested these to be potential candidates for immunoprophylaxis against leishmaniasis. In this study, we investigated the protective efficacy of purified recombinant proteins from two of the identified cDNA clones along with the adjuvant MPL, in a hamster model of experimental leishmaniasis. We demonstrate here that the immunization of animals with one of the recombinant proteins (rF14) having 97% similarity to C1 clone of L. chagasi ribosomal protein gene P0 (rLiP0) along with MPL provided partial protection against the virulent challenge of L. donovani. The absence of antigen-specific lymphoproliferative responses in these immunized animals may be responsible for the lack of complete and long-lasting protection.     

An Evolutionarily Conserved Family of Virion Tail Needles Related to Bacteriophage P22 gp26: Correlation between Structural Stability and Length of the α-Helical Trimeric Coiled Coil

Bacteriophages of the Podoviridae family use short noncontractile tails to inject their genetic material into Gram-negative bacteria. In phage P22, the tail contains a thin needle, encoded by the phage gene 26, which is essential both for stabilization and for ejection of the packaged viral genome. Bioinformatic analysis of the N-terminal domain of gp26 (residues 1-60) led us to identify a family of genes encoding putative homologues of the tail needle gp26. To validate this idea experimentally and to explore their diversity, we cloned the gp26-like gene from phages HK620, Sf6 and HS1, and characterized these gene products in solution. All gp26-like factors contain an elongated α-helical coiled-coil core consisting of repeating, adjacent trimerization heptads and form trimeric fibers with length ranging between about 240 to 300 Å. gp26 tail needles display a high level of structural stability in solution, with T_m (temperature of melting) between 85 and 95 °C. To determine how the structural stability of these phage fibers correlates with the length of the α-helical core, we investigated the effect of insertions and deletions in the helical core. In the P22 tail needle, we identified an 85-residue-long helical domain, termed MiCRU (minimal coiled-coil repeat unit), that can be inserted in-frame inside the gp26 helical core, preserving the straight morphology of the fiber. Likewise, we were able to remove three quarters of the helical core of the HS1 tail needle, minimally decreasing the stability of the fiber. We conclude that in the gp26 family of tail needles, structural stability increases nonlinearly with the length of the α-helical core. Thus, the overall stability of these bacteriophage fibers is not solely dependent on the number of trimerization repeats in the α-helical core.     

In Vitro Priming Recapitulates In Vivo HIV-1 Specific T Cell Responses,Revealing Rapid Loss of Virus Reactive CD4+ T Cells in Acute HIV-1 Infection

Background

The requirements for priming of HIV-specific T cell responses initially seen in infected individuals remain to be defined. Activation of T cell responses in lymph nodes requires cell-cell contact between T cells and DCs, which can give concurrent activation of T cells and HIV transmission.

Methodology

The study aim was to establish whether DCs pulsed with HIV-1 could prime HIV-specific T cell responses and to characterize these responses. Both infectious and aldrithiol-2 inactivated noninfectious HIV-1 were compared to establish efficiencies in priming and the type of responses elicited.

Findings

Our findings show that both infectious and inactivated HIV-1 pulsed DCs can prime HIV-specific responses from naïve T cells. Responses included several CD4⁺ and CD8⁺ T cell epitopes shown to be recognized in vivo by acutely and chronically infected individuals and some CD4⁺ T cell epitopes not identified previously. Follow up studies of acute and recent HIV infected samples revealed that these latter epitopes are among the earliest recognized in vivo, but the responses are lost rapidly, presumably through activation-induced general CD4⁺ T cell depletion which renders the newly activated HIV-specific CD4⁺ T cells prime targets for elimination.

Conclusion

Our studies highlight the ability of DCs to efficiently prime naïve T cells and induce a broad repertoire of HIV-specific responses and also provide valuable insights to the pathogenesis of HIV-1 infection in vivo.