Alpine vascular plant species richness: the importance of daily maximum temperature and pH

Species richness in the alpine zone varies dramatically when communities are compared. We explored (i) which stress and disturbance factors were highly correlated with species richness, (ii) whether the intermediate stress hypothesis (ISH) and the intermediate disturbance hypothesis (IDH) can be applied to alpine ecosystems, and (iii) whether standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone. Species numbers and standing crop were determined in 14 alpine plant communities in the Swiss Alps. To quantify the stress and disturbance factors in each community, air temperature, relative air humidity, wind speed, global radiation, UV-B radiation, length of the growing season, soil suction, pH, main soil nutrients, waterlogging, soil movement, number of avalanches, level of denudation, winter dieback, herbivory, wind damage, and days with frost were measured or observed. The present study revealed that 82% of the variance in␣vascular species richness among sites could be explained by just two abiotic factors, daily maximum temperature and soil pH. Daily maximum temperature and pH affect species richness both directly and via their effects on other environmental variables. Some stress and disturbance factors were related to species richness in a monotonic way, others in an unimodal way. Monotonic relationships suggest that the harsher the environment is, the fewer species can survive in such habitats. In cases of unimodal relationships (ISH and IDH) species richness decreases at both ends of the gradients due to the harsh environment and/or the interaction of other environmental factors. Competition and disturbance seemed only to play a secondary role in the form of fine-tuning species richness in specific communities. Thus, we concluded that neither the ISH nor the IDH can be considered useful conceptual models for the alpine zone. Furthermore, we found that standing crop can be used as an easily measurable surrogate for causal factors determining species richness in the alpine zone, even though there is no direct causality.     

Activated T lymphocytes resist the toxic effects of the adenosine deaminase inhibitor, 2-deoxycoformycin

Tonsil lymphocytes from three adults and three children were examined for immunoglobulin (Ig) production before and after Epstein-Barr virus (EBV) transformation. T-cell depletion was required to obtain cell lines from EBV-seropositive individuals. Cytoplasmic Ig was mainly IgG in adult lymphocytes before and after transformation; IgA and IgM were more prominent after than before. IgM and IgG predominated in lymphocytes of children before and after transformation; IgA was more prominent after than before. Cytoplasmic Ig of peripheral blood lymphocytes from these individuals was mainly IgM. Secreted Ig from tonsil lymphocytes was mainly IgA or IgG; after transformation IgM predominated with adult cell lines, and IgG or IgM with cell lines from children. IgE was consistently sparse in spite of ragweed and/or grass allergies of the adults.     

Altered lymphocyte functions in rats bearing syngeneic Moloney sarcoma tumors. I. Mitogen responses, mixed lymphocyte reactions (MLR) and mixed lymphocyte-tumor reactions (MLTR).

Impairment of mitogen responses to Con A and LPS and of MLR and MLTR was detected in the spleens of rats bearing syngeneic Moloney sarcoma tumors. Depressed responses of both T cell and Ig+ cell populations were observed. During the observation period of 6 to 10 days post-tumor inoculation when maximal T cell-mediated cytotoxicity was observed in spleen and draining lymph node cells, spleen cells showed marked impairment in response to stimuli mentioned above. By contrast, draining lymph node cell activity was either unaltered or somewhat elevated above the level of activity measured in normal control populations. Data presented in this and an accompanying paper strongly indicate that macrophages are activated as immunosuppressor cells in tumor-bearing rats.     

Human TLR8 senses UR/URR motifs in bacterial and mitochondrial RNA

Toll‐like receptor (TLR) 13 and TLR2 are the major sensors of Gram‐positive bacteria in mice. TLR13 recognizes Sa19, a specific 23S ribosomal (r) RNA‐derived fragment and bacterial modification of Sa19 ablates binding to TLR13, and to antibiotics such as erythromycin. Similarly, RNase A‐treated Staphylococcus aureus activate human peripheral blood mononuclear cells (PBMCs) only via TLR2, implying single‐stranded (ss) RNA as major stimulant. Here, we identify human TLR8 as functional TLR13 equivalent that promiscuously senses ssRNA. Accordingly, Sa19 and mitochondrial (mt) 16S rRNA sequence‐derived oligoribonucleotides (ORNs) stimulate PBMCs in a MyD88‐dependent manner. These ORNs, as well as S. aureus‐, Escherichia coli‐, and mt‐RNA, also activate differentiated human monocytoid THP‐1 cells, provided they express TLR8. Moreover, Unc93b1 ^−/−‐ and Tlr8 ^−/−‐THP‐1 cells are refractory, while endogenous and ectopically expressed TLR8 confers responsiveness in a UR/URR RNA ligand consensus motif‐dependent manner. If TLR8 function is inhibited by suppression of lysosomal function, antibiotic treatment efficiently blocks bacteria‐driven inflammatory responses in infected human whole blood cultures. Sepsis therapy might thus benefit from interfering with TLR8 function.     

Cytosolic RNA:DNA hybrids activate the cGAS–STING axis

Intracellular recognition of non‐self and also self‐nucleic acids can result in the initiation of potent pro‐inflammatory and antiviral cytokine responses. Most recently, cGAS was shown to be critical for the recognition of cytoplasmic dsDNA. Binding of dsDNA to cGAS results in the synthesis of cGAMP(2′–5′), which then binds to the endoplasmic reticulum resident protein STING. This initiates a signaling cascade that triggers the induction of an antiviral immune response. While most studies on intracellular nucleic acids have focused on dsRNA or dsDNA, it has remained unexplored whether cytosolic RNA:DNA hybrids are also sensed by the innate immune system. Studying synthetic RNA:DNA hybrids, we indeed observed a strong type I interferon response upon cytosolic delivery of this class of molecule. Studies in THP‐1 knockout cells revealed that the recognition of RNA:DNA hybrids is completely attributable to the cGAS–STING pathway. Moreover, in vitro studies showed that recombinant cGAS produced cGAMP upon RNA:DNA hybrid recognition. Altogether, our results introduce RNA:DNA hybrids as a novel class of intracellular PAMP molecules and describe an alternative cGAS ligand next to dsDNA.     

Surfactant protein D increases phagocytosis and aggregation of pollen-allergen starch granules

Recent studies have shown that surfactant components, in particular the collectins surfactant protein (SP)-A and -D, modulate the phagocytosis of various pathogens by alveolar macrophages. This interaction might be important not only for the elimination of pathogens but also for the elimination of inhaled allergens and might explain anti-inflammatory effects of SP-A and SP-D in allergic airway inflammation. We investigated the effect of surfactant components on the phagocytosis of allergen-containing pollen starch granules (PSG) by alveolar macrophages. PSG were isolated from Dactylis glomerata or Phleum pratense, two common grass pollen allergens, and incubated with either rat or human alveolar macrophages in the presence of recombinant human SP-A, SP-A purified from patients suffering from alveolar proteinosis, a recombinant fragment of human SP-D, dodecameric recombinant rat SP-D, or the commercially available surfactant preparations Curosurf and Alveofact. Dodecameric rat recombinant SP-D enhanced binding and phagocytosis of the PSG by alveolar macrophages, whereas the recombinant fragment of human SP-D, SP-A, or the surfactant lipid preparations had no effect. In addition, recombinant rat SP-D bound to the surface of the PSG and induced aggregation. Binding, aggregation, and enhancement of phagocytosis by recombinant rat SP-D was completely blocked by EDTA and inhibited by d-maltose and to a lesser extent by d-galactose, indicating the involvement of the carbohydrate recognition domain of SP-D in these functions. The modulation of allergen phagocytosis by SP-D might play an important role in allergen clearance from the lung and thereby modulate the allergic inflammation of asthma.     

Immunoregulatory activity of culture-induced suppressor macrophages

Rat splenic cells precultured in vitro for 5 days exhibited marked suppressive activity on the secondary cytotoxic T lymphocyte (CTL) response to a Gross virus-induced lymphoma. Suppressive activity was produced by macrophages (MØ) rather than lymphocytes and as low as 1% MØ content was sufficient to achieve completely inhibited CTL responses. Aspirin, indomethacin, and d,l-6-chloro-2-methylcarbazole-2-acetic acid prevented cultured splenic MØ from exerting their inhibitory effect, thereby suggesting a role for prostaglandins in suppression. Events which occurred within the first 24 to 48 hr of the CTL response were susceptible to the suppressive action of MØ since normal CTL responses were obtained if suppressive MØ were added later than Day 2 or if indomethacin was added within the first 24 to 48 hr of culture. Two processes of lymphocyte activation, namely blast transformation and DNA synthesis, were inhibited in the presence of suppressive MØ. However, suppression of these processes did not result in the loss of CTL progenitor cells since CTL responses that were inhibited in the presence of suppressive MØ proceeded normally following their removal.