Recurrent Respiratory Syncytial Virus Infection in a CD14-Deficient Patient

BACKGROUND

Recurrent respiratory syncytial virus (RSV) infection requiring hospitalization is rare and the underlying mechanism is unknown. We aimed to determine the role of CD14-mediated immunity in the pathogenesis of recurrent RSV infection.

METHODS

We performed genotyping and longitudinal immunophenotyping of the first patient with a genetic CD14 deficiency who developed recurrent RSV infection. We analyzed gene expression profiles and interleukin (IL)-6 production by patient peripheral blood mononuclear cells in response to RSV pre- and post-fusion (F) protein. We generated CD14-deficient human nasal epithelial cells cultured at air-liquid interface (HNEC-ALI) of patient-derived cells and after CRISPR-based gene editing of control cells. We analyzed viral replication upon RSV infection.

RESULTS

Sanger sequencing revealed a homozygous single-nucleotide deletion in CD14, resulting in absence of the CD14 protein in the index patient. In vitro, viral replication was similar in wild-type and CD14-/- HNEC-ALI. Loss of immune cell CD14 led to impaired cytokine and chemokine responses to RSV pre- and post-F protein, characterized by absence of IL-6 production.

CONCLUSIONS

We report an association of recurrent RSV bronchiolitis with a loss of CD14 function in immune cells. Lack of CD14 function led to defective immune responses to RSV pre- and post-F protein without a change in viral replication.

Transport of activated fatty acids by the peroxisomal ATP-binding-cassette transporter Pxa2 in a semi-intact yeast cell system

In the yeast Saccharomyces cerevisiae, fatty acid beta-oxidation is restricted to peroxisomes. Previous studies have shown two possible routes by which fatty acids enter the peroxisome. The first route involves transport of medium-chain fatty acids across the peroxisomal membrane as free fatty acids, followed by activation within the peroxisome by Faa2p, an acyl-CoA synthetase. The second route involves transport of long-chain fatty acids. Long-chain fatty acids enter the peroxisome via a route that involves activation in the extraperoxisomal space, followed by transport across the peroxisomal membrane. It has been suggested that this transport is dependent upon the peroxisomal ATP-binding-cassette transporters Pxa1p and Pxa2p. In this paper we investigated whether Pxa2p is directly responsible for the transport of C18:1-CoA, a long-chain acyl-CoA ester. Using protoplasts in which the plasma membrane has been selectively permeabilised by digitonin, we show that C18:1-CoA, but not C8:0-CoA, enters the peroxisome via Pxa2p, in an ATP-dependent fashion. The results obtained may contribute to the elucidation of the primary defect in the human disease X-linked adrenoleukodystrophy.

Cytosolic aspartate aminotransferase encoded by the AAT2 gene is targeted to the peroxisomes in oleate-grown Saccharomyces cerevisiae

Fatty acid beta-oxidation in peroxisomes requires the continued uptake of fatty acids or their derivatives into peroxisomes and export of beta-oxidation products plus oxidation of NADH to NAD. In an earlier study we provided evidence for the existence of an NAD(H) redox shuttle in which peroxisomal malate dehydrogenase plays a pivotal role. In analogy to the NAD(H)-redox-shuttle systems in mitochondria we have investigated whether a malate/aspartate shuttle is operative in peroxisomes. The results described in this paper show that peroxisomes of oleate-grown Saccharomyces cerevisiae contain aspartate aminotransferase (AAT) activity. Whereas virtually all cellular AAT activity was peroxisomal in oleate-grown cells, we found that in glucose-grown cells most of the AAT activity resided in the cytosol. We demonstrate that the gene AAT2 codes for the cytosolic and peroxisomal AAT activities. Disruption of the AAT2 gene did not affect growth on oleate. Furthermore beta-oxidation of palmitate was normal. These results indicate that AAT2 is not essential for the peroxisomal NAD(H) redox shuttle.

Permeability properties of peroxisomes in digitonin-permeabilized rat hepatocytes. Evidence for free permeability towards a variety of substrates

In order to investigate the permeability properties of rat-liver peroxisomes in situ, we selectively permeabilized hepatocytes with digitonin in a medium mimicking the cytosol. This system permitted us to study the latency of peroxisomal oxidases by means of measurement of their activities in permeabilized compared to disrupted hepatocytes. The activity of peroxisomal oxidases was studied using three different methods: (1) measurement of the oxidase-mediated production of H2O2 in a system containing homovanillic acid, horseradish peroxidase and azide; (2) measurement of the rate of substrate utilization or product formation; (3) measurement of the production of H2O2 via the peroxidative action of catalase in the presence of an excess of methanol. The results obtained depended on which system was used to measure the activity of the different oxidases. Our observations lead us to conclude that method 1 cannot be used for latency studies, whereas methods 2 and 3 are suitable under defined circumstances. Based on the results of methods 2 and 3, we conclude that urate oxidase, L-alpha-hydroxyacid oxidase A and D-amino acid oxidase show no structure-linked latency in digitonin-permeabilized hepatocytes, suggesting that the substrates for these enzymes permeate freely through the peroxisomal membrane.