Producing Human Therapeutic Proteins in Plastids

Plastid transformation technology is set to become a major player in the production of human therapeutic proteins. Protein expression levels that can be achieved in plant plastids are hundreds of times greater than the expression levels generally obtained via nuclear transformation. Plastids can produce human proteins that are properly folded and are biologically active. Effective protein purification strategies and strategies that can achieve inducible plastid gene expression are being developed within the system. Plastid transformation technology has been extended to edible plant species, which could minimize down-stream processing costs and raises the possibility of “edible protein therapies”. The system is limited by the fact that plastid-produced proteins are not glycosylated and that, at the moment, it can be difficult to predict protein stability within the plastid. The high level of protein expression that can be obtained in plastids could make it possible to produce high-value therapeutic proteins in plants on a scale that could be accommodated in contained glasshouse facilities and still be economically viable. Growing plastid-transformed plants under contained conditions, and coupled with the level of bio-safety conferred by maternal inheritance of plastid transgenes, would address many of the social and environmental concerns relating to plant based production of human therapeutic proteins

Mannose-Binding Lectin Binds to Amyloid Protein and Modulates Inflammation

Mannose-binding lectin (MBL), a soluble factor of the innate immune system, is a pattern recognition molecule with a number of known ligands, including viruses, bacteria, and molecules from abnormal self tissues. In addition to its role in immunity, MBL also functions in the maintenance of tissue homeostasis. We present evidence here that MBL binds to amyloid β peptides. MBL binding to other known carbohydrate ligands is calcium-dependent and has been attributed to the carbohydrate-recognition domain, a common feature of other C-type lectins. In contrast, we find that the features of MBL binding to Aβ are more similar to the reported binding characteristics of the cysteine-rich domain of the unrelated mannose receptor and therefore may involve the MBL cysteine-rich domain. Differences in MBL ligand binding may contribute to modulation of inflammatory response and may correlate with the function of MBL in processes such as coagulation and tissue homeostasis

WTA immunization reduces MW2 CA-MRSA infection in WT mice while no difference is seen in the absence of MBL.

<p>(2A) Abscess formation. Mice immunized with PBS control or WTA were infected 20 days after the last immunization. Abscess formation was examined on day 10 following systemic infection with MW2 CA-MRSA as detailed in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069739#s2" target="_blank">Materials and Methods</a>. Abscess formation is expressed as numbers of mice with abscess and total mice in each group. * indicates p<0.0001 against all other groups (Likelihood Ratio). (2B) Bacterial load in the kidney. Bacterial titers were measured in homogenates of two combined kidneys and are expressed as cfu/g of kidneys in a box plot. Numbers of mice used are as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069739#pone-0069739-g002" target="_blank">figure 2A</a>. * and ** indicates p<0.05 and p<0.001, respectively compared to WT immunized with PBS control (Nonparametric comparisons for each pair by Wilcoxon methods).</p

Abscess formation in systemic MRSA infection.

*<p>indicates p<0.0001 (Likelihood ratio) compared to WT in MW2 CA-MRSA infection.</p

Serum from WTA-immunized mice inhibits bacterial growth in whole blood assays <i>ex vivo</i>.

<p>Two MRSA strains, COL HA-MRSA (4A and 4B) and MW2 CA-MRSA, (4C and 4D) were used. Bacteria were incubated with whole blood from MBL KO (4A and 4C) or WT mice (4B and 4D) with serum from MBL KO mice immunized with either PBS control or WTA, as described in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069739#s2" target="_blank">Materials and Methods</a>. Bacterial titers are expressed as mean <b>±</b> SD in each group of four samples. Each sample was measured in duplicate and the average measurement was used for statistical analysis. Representative results from two repeated experiments are shown. *, **, and *** indicate p<0.05, 0.001, and 0.0001 (Student's t-test), respectively.</p