Soft X-ray microscopy analysis of cell volume and hemoglobin content in erythrocytes infected with asexual and sexual stages of Plasmodium falciparum

Plasmodium falciparum, the most virulent agent of human malaria, undergoes both asexual cycling and sexual differentiation inside erythrocytes. As the intraerythrocytic parasite develops it increases in size and alters the permeability of the host cell plasma membrane. An intriguing question is: how is the integrity of the host erythrocyte maintained during the intraerythrocytic cycle? We have used water window cryo X-ray tomography to determine cell morphology and hemoglobin content at different stages of asexual and sexual differentiation. The cryo stabilization preserves native structure permitting accurate analyses of parasite and host cell volumes. Absorption of soft X-rays by protein adheres to Beer–Lambert’s law permitting quantitation of the concentration of hemoglobin in the host cell compartment. During asexual development the volume of the parasite reaches about 50% of the uninfected erythrocyte volume but the infected erythrocyte volume remains relatively constant. The total hemoglobin content gradually decreases during the 48 h cycle but its concentration remains constant until early trophozoite stage, decreases by 25%, then remains constant again until just prior to rupture. During early sexual development the gametocyte has a similar morphology to a trophozoite but then undergoes a dramatic shape change. Our cryo X-ray tomography analysis reveals that about 70% of the host cell hemoglobin is taken up and digested during gametocyte development and the parasite eventually occupies about 50% of the uninfected erythrocyte volume. The total volume of the infected erythrocyte remains constant, apart from some reversible shrinkage at stage IV, while the concentration of hemoglobin decreases to about 70% of that in an uninfected erythrocyte.     

The twists and turns of Maurer's cleft trafficking in P. falciparum-infected erythrocytes

The malaria parasite, Plasmodium falciparum, invades the red blood cells (RBCs) of its human host and initiates a series of morphological rearrangements within the host cell cytoplasm. The mature RBC has no endogenous trafficking machinery; therefore, the parasite generates novel structures to mediate protein transport. These include compartments called the Maurer's clefts (MC), which play an important role in the trafficking of parasite proteins to the surface of the host cell. Recent electron tomography studies have revealed MC as convoluted flotillas of flattened discs that are tethered to the RBC membrane, prompting speculation that the MC could, in one respect, represent an extracellular equivalent of the Golgi apparatus. Visualization of both resident and cargo proteins has helped decipher the signals and routes for trafficking of parasite proteins to the MC and beyond.     

A label of health: a previous immune challenge is reflected in the expression of a female plumage trait

Studies of ornaments as indicators of individual quality have hitherto focused on males, while studies of female ornaments have been almost absent. However, females within the same species may show large variation in both outer appearance and individual quality. We experimentally examined the effect of an immune challenge on the size of white fringes in the wing feathers produced one to two months after the challenge in female common eiders (Somateria mollissima), a long-lived sea duck. Immune-challenged females produced feathers with smaller white fringes, showing that a previous immune challenge may affect the expression of a plumage trait. We also report an unexpected difference in the expression of this white plumage trait within the immune-challenged group, related to the specific immune response against one of the injected antigens.     

Immune-Mediated Fever in the Dog. Occurrence of Antinuclear Antibodies, Rheumatoid Factor, Tumor Necrosis Factor and Interleukin-6 in Serum

Contents of antinuclear antibodies (ANA), rheumatoid factor (RF), tumor necrosis factor (TNF-α) and interleukin-6 (IL-6) were measured in serum from 20 dogs with immune-mediated fever. Seven out of 20 patients were ANA positive, 1 out of 20 was positive to antibodies against extractable nuclear antigens (ENA), 1 out of 20 was positive to antibodies against deoxynucleoproteins (DNP), 2 out of 13 were RF positive and none out of 20 patients had antibodies against native DNA in the serum. TNF-α was not detected in any serum of 15 dogs with immune-mediated fever, while 10 out of 13 presented with elevated IL-6. The results varied between patients, but the IL-6 level was high in most of them. This indicate a role for IL-6 in the pathogenesis of immune-mediated fever in most cases.     

Molecular interactions of biglycan and decorin with elastic fiber components: biglycan forms a ternary complex with tropoelastin and microfibril-associated glycoprotein 1.

The interactions of the dermatan sulfate proteoglycans biglycan and decorin have been investigated with the elastic fiber components, tropoelastin, fibrillin-containing microfibrils, and microfibril-associated glycoproteins (MAGP) 1 and 2. Both proteoglycans were found to bind tropoelastin and fibrillin-containing microfibrils but not MAGPs 1 and 2 in solid phase binding assays. The specificity of the binding of biglycan and decorin to tropoelastin was confirmed by co-immunoprecipitation experiments and by the blocking of the interactions with elastin-derived peptides. Isolated core proteins from biglycan and decorin bound to tropoelastin more strongly than the intact proteoglycans, and there were no differences in the tropoelastin binding characteristics of distinct glucuronate-rich and iduronate-rich glycoforms of biglycan. These findings indicated that the binding sites were contained in the protein cores of the proteoglycans rather than the glycosaminoglycan side chains. Scatchard analysis showed that biglycan bound more avidly than decorin to tropoelastin with K(d) values estimated as 1.95 x 10(-7) m and 5.3 x 10(-7) m, respectively. In blocking experiments each proteoglycan showed extensive inhibition of binding of the other to tropoelastin but was most effective at blocking its own binding. This result suggested that biglycan and decorin had closely spaced but distinct binding sites on tropoelastin. Addition of the elastin-binding protein MAGP-1 to the assays enhanced the binding of biglycan to tropoelastin but had no effect on the decorin-tropoelastin interaction. Co-immunoprecipitation experiments showed that MAGP-1 interacted with biglycan but not decorin in the solution phase. The results indicated that biglycan specifically formed a ternary complex with tropoelastin and MAGP-1. Overall the study supports the concept that biglycan may have a specific role in the elastinogenic phase of elastic fiber formation.     

The Agnogene of the Human Polyomavirus BK Is Expressed

Primate polyomavirus genomes all contain an open reading frame at the 5′ end of the late coding region called the agnogene. A simian virus 40 agnoprotein with unknown functions has previously been demonstrated. We now show that a BK virus agnoprotein appears in the perinuclear area and cytoplasm late in the infectious cycle. It is phosphorylated in vivo and coimmunoprecipitates with a subset of host cell proteins.     

Costs of parasites in common eiders: effects of antiparasite treatment

Parasites are exploiting their host for the resources required for the parasite's reproduction and survival. The effects of antiparasitic treatment during incubation on body mass and return rate in female common eiders Somateria mollissima were examined in a two year study (1998 and 1999) . There was no effect of treatment on nest success, but unsuccessful females had lower body mass. Treatment had no effect on incubation time, mass-loss during incubation or return rate among successful birds. However, treatment lead to higher return rate among unsuccessful birds (treated=69%, n=13; controls=18%, n=11). This pattern remained significant also after including the birds that returned two years after the experiment. We suggest that the unsuccessful females are of lower quality and had higher costs from parasite infections than birds which completed incubation, and that the higher return rate for treated unsuccessful females may mean that costs of parasites are substantial, and that the potential fitness gain from investment in parasite defense and avoidance is large.     

Ocean acidification ameliorates harmful effects of warming in primary consumer

Climate change‐induced warming and ocean acidification are considered two imminent threats to marine biodiversity and current ecosystem structures. Here, we have for the first time examined an animal's response to a complete life cycle of exposure to co‐occurring warming (+3°C) and ocean acidification (+1,600 μatm CO₂), using the key subarctic planktonic copepod, Calanus finmarchicus, as a model species. The animals were generally negatively affected by warming, which significantly reduced the females’ energy status and reproductive parameters (respectively, 95% and 69%–87% vs. control). Unexpectedly, simultaneous acidification partially offset the negative effect of warming in an antagonistic manner, significantly improving reproductive parameters and hatching success (233%–340% improvement vs. single warming exposure). The results provide proof of concept that ocean acidification may partially offset negative effects caused by warming in some species. Possible explanations and ecological implications for the observed antagonistic effect are discussed.