Comparison of recombinant protein Z with natural protein Z derived from malt: From structure to functional properties.

Protein Z (PZ) is a prominent albumin found in the endosperm of barley seeds with a molecular weight of approximately 40 kDa. Its multifaceted functional attributes, including trypsin- and thrombin-inhibiting bioactivities and superior foaming properties, have garnered significant attention in research. Considering the post-translational modifications of PZ natural in barley malt, we tried to express recombinant protein Z (rPZ) in E. coli. The present study aims to undertake a comparative analysis between natural PZ and rPZ in order to elucidate their respective characteristics. After spectral analysis, there are significant differences in their secondary and tertiary structures. In addition, rPZ showed superior foamability and foam stability. As for the serpin-like activity, the inhibition rate of rPZ is much higher than that of PZ. In contrast with the inhibition activity, the digestability of rPZ is much lower than that of PZ. As for the cargo carrier properties, rPZ showed an excellent ability to stabilize astaxanthin at 37 °C. These results suggest that rPZ is more suitable as protein carrier, due to the high foamability, serpin-like activity and low digestive stability, which not only give a brief view of recombinant protein, but also give a direction for PZ in cargo delivery.

Amniotic Fluid Proteomics Analysis and In Vitro Validation to Identify Potential Biomarkers of Preterm Birth.

This study aimed to investigate the regulation of amniotic fibroblast (AFC) function by vitamin K-dependent protein Z (PROZ) during preterm birth (PTB) and its potential role in adverse pregnancy outcomes. Proteomic samples were collected from amniotic fluid in the second trimester, and AFC were isolated from the amniotic membrane and cultured in vitro. The expression of extracellular and intracellular PROZ in AFC was modulated, and their biological properties and functions were evaluated. Clinical analysis revealed a significant upregulation of PROZ expression in amniotic fluid from preterm pregnant women. In vitro experiments demonstrated that PROZ stimulated AFC migration, enhanced their proliferative capacity, and reduced collagen secretion. Overexpression of PROZ further enhanced cell migration and proliferation, while knockdown of PROZ had the opposite effect. PROZ plays a crucial role in promoting the proliferation and migration of amniotic membrane fibroblasts. Increased PROZ expression in amniotic fluid is associated with the occurrence of PTB. These findings shed light on the potential involvement of PROZ in adverse pregnancy outcomes and provide a basis for further research on its regulatory mechanisms during PTB.

Chicoric acid inserted in protein Z cavity exhibits higher stability and better wound healing effect under oxidative stress.

Oxidative stress is one of the limiting factors that inhibit wound healing. Phytochemicals especially chicoric acid have the potential to act as an antioxidant and scavenge reactive oxygen species, thereby promoting wound healing. However, most of the phytochemicals were easy to be degraded during storage or using due to the oxidative status in wound site. Herein, we introduce a high stable protein Z that can encapsulate chicoric acid during foaming. TEM results showed that the size of protein Z-chicoric acid is in the range of nanoscale (named PZ-CA nanocomposite), and protein Z encapsulation can significantly improve the stability of chicoric acid under oxidative stress. Moreover, PZ-CA nanocomposite exhibited favorable antioxidant properties, biocompatibility, and the ability to promote cell migration in vitro. The role of PZ-CA nanocomposite in skin regeneration was explored by a mice model. Results in vivo suggest that the PZ-CA nanocomposite promotes wound healing with a faster rate as compared with a commercial spray solution, mostly through attenuating the oxidative stress, promoting cell proliferation and collagen deposition. This work not only provides a delivery vector for bioactive molecules, but also develops a kind of nanocomposite with the property of promoting wound healing.

Ligand-based pharmacophore modelling, virtual screening and docking studies to identify potential compounds against FtsZ of Mycobacterium tuberculosis.

BACKGROUND AND INTRODUCTION: Tuberculosis (TB) is caused by Mycobacterium tuberculosis (M.tb) which is the most common cause of death from bacterial illness. Millions of victims of TB infections have been recorded including 20,800 deaths amongst HIV positive individuals. Hence, there is a rising need for new and active compounds against M. tb protein targets especially as there is a persistent resistance to the current drug treatment regime. AIM: This study identifies new potential compounds against the M. tb target protein ftsZ via pharmacophore modelling, QSAR analysis and docking studies. METHOD: Inhibitors with known PIC50 were used as a training set and the pharmacophore features (1 aromatic center, 2 hydrophobic, 2 hydrogen bond acceptors and 1 hydrogen bond donor) were validated against four test set compounds. The identified hits were subjected to rigorous ADMET properties and docked using PyRx. DS visualizer was used in binding interactions study. Stability was measured based on the total number of interactions and preference given to the number of hydrogen bond interactions. RESULTS: Based on the number of interactions, hydrogen bonds, extensive virtual screening and ADMET filtration, 40 compounds have been identified as potential inhibitors of ftsZ with only 3 considered to be the best leads. SIGNIFICANCE OF RESEARCH: The identified compounds have potential of being drug candidate against Mycobacterium tuberculosis and may possess a novel mechanistic route in inhibiting the resistant strains.

Protein Z and Protein Z-dependent protease inhibitor in patients with acute ischemic stroke: A prospective mechanistic study.

OBJECTIVES: Protein Z (PZ) /Protein Z-dependent protease inhibitor (ZPI) (PZ/ZPI) system is a new anticoagulant system discovered in recent years, which plays an important role in many diseases. We aimed to compare the plasma PZ/ZPI levels of acute ischemic stroke (AIS) patients and non-stroke control participants and the role of PZ/ZPI in the development of stroke was preliminarily analyzed. MATERIALS AND METHODS: Enzyme linked immunosorbent assay (ELISA) was used to detect and compare plasma PZ levels of 86 patients with acute AIS and 85 non-stroke control patients. Multivariable Logistic regression was used to analyze whether PZ was an independent risk factor for AIS. RESULTS: In the present study, plasma PZ is closely related to inflammatory response, coagulation process and platelet activation, and may participate in the development of AIS by inducing inflammatory responses and interfering with the coagulation process. CONCLUSIONS: Our results suggested that plasma PZ level is one of the independent risk factors of AIS, and plasma ZPI was closely related to coagulation and platelet parameter and may play a role in the coagulation process during AIS.

Protein Z modulates the metastasis of lung adenocarcinoma cells.

Protein Z (PZ), a vitamin-K-dependent anticoagulant glycoprotein, is reported to be highly expressed in various malignant tissues and correlated with a poor prognosis in patients with lung cancer. This study aimed to investigate the pathological activity of PZ on lung cancer cell migration, invasion, and metastasis. PZ was assessed by Western blot in three non-small-cell lung cancer cell lines (A549, H1299, and H1975). Meanwhile,western blot was used to detect the expression of EMT pathway-related proteins (Slug, Vimentin, and N-cadherin) in the A549 cells knocked down with siRNA. The cellular proliferation, migration, and invasion were detected by Cell Counting Kit (CCK)-8, wound healing, and Transwell assays in the A549 cells. The results showed that PZ expression was higher in A549, H1299, and H1975 cells, according to Western blot. CCK-8, wound healing, and Transwell assays showed that knockdown of PZ significantly decreased cellular proliferation, migration, and invasion, as well as the protein levels of Slug, Vimentin, and N-cadherin in the A549 cells. In conclusion, the pro-metastasis activity of PZ may modulate the epithelial-mesenchymal transition pathway in lung cancer A549 cells.

Plasma levels and urinary excretion of protein Z in patients with urolithiasis.

OBJECTIVES: Protein Z (PZ) is a γ-carboxyglutamic acid protein present in plasma that is involved in blood coagulation. Detailed analysis of urinary stones from patients with urolithiasis has revealed that PZ is often found in urinary stones composed of calcium oxalate monohydrate. In this study, we compared blood and urinary PZ concentrations between healthy individuals and patients with urolithiasis. METHODS: Plasma and urine were collected from healthy individuals and patients with urolithiasis who provided informed consent. PZ was detected as a urinary stone matrix protein in some of the patients. PZ was quantified by ELISA, creatinine was measured by the enzymatic method, and the total protein concentration was measured by the Bradford method. RESULTS: The plasma PZ level was 2.54 ± 1.02 µg/mL in healthy individuals and that in urolithiasis patients classified by stone history were from 1.16 ± 0.77 to 3.73 ± 1.09 µg/mL, which was not significantly different. The urinary excretion of PZ (PZ/creatinine) was also not different in patients with urolithiasis and in healthy individuals (from 54.1 ± 40.9 to 95.4 ± 69.4 ng/mg vs. 73.3 ± 36.0 ng/mg). A positive correlation was found between the plasma PZ level and creatinine-corrected urinary PZ concentration (r = 0.46). CONCLUSIONS: Both the plasma level and urinary excretion of PZ in urolithiasis patients were not significantly different with normal individuals. PZ detected in urinary stones as a matrix protein is thought to be incorporated into urinary stones regardless of blood and urine levels of PZ.

Inhibition of Iron Release from Donkey Spleen Ferritin through Malt-Derived Protein Z-Ferulic Acid Interactions.

Protein-small molecule interactions naturally occur in foodstuffs, which could improve the properties of protein and small molecules. Meanwhile, they might affect the bioavailability and nutritional value of proteins. Ferritin, as an iron-storage protein, has been a focus of research. However, the complexity of foodstuffs enables the interaction between ferritin and food components, especially polyphenols, which can induce iron release from ferritin. Thus, the application of ferritin in food is limited. Inspired by the natural-occurring, strong protein-polyphenol interactions in beer, to inhibit the iron release of ferritin, the malt-derived protein Z (PZ) was chosen to interact with ferulic acid (FA), an abundant reductant in malt, beer, and other foodstuffs. The analysis of the interaction between PZ and FA was carried out using fluorescence spectroscopy, the results of which suggest that one PZ molecule can bind with 22.11 ± 2.13 of FA, and the binding constant is (4.99 ± 2.13) × 105 M-1. In a molecular dynamics (MD) simulation, FA was found to be embedded in the internal hydrophobic pocket of PZ, where it formed hydrogen bonds with Val-389 and Tyr-234. As expected, compared to iron release induced by FA, the iron release from donkey spleen ferritin (DSF) induced by FA decreased by 86.20% in the presence of PZ. Meanwhile, based on the PZ-FA interaction, adding PZ in beer reduced iron release from DSF by 40.5% when DSF:PZ was 1:40 (molar ratio). This work will provide a novel method of inhibiting iron release from ferritin.

Binding of curcumin to barley protein Z improves its solubility, stability and bioavailability.

Although excessive pharmaceutical activities of curcumin have been reported, the poor solubility, low stability and low bioavailability greatly limited its application. In this study, the interaction between protein Z (PZ) and curcumin, and the effects of PZ on the stability and bioavailability of curcumin were investigated. Fluorescence quenching results indicated that curcumin molecule binds PZ with a stoichiometry of 4:1, and the binding affinity is stronger than other reported protein carriers. Molecular dynamics simulation results suggested that curcumin binds in the hydrophobic region of PZ, and the interaction was maintained mainly by hydrogen-bond (Pro-287, Asn-340 and Tyr-234). PZ-curcumin complex possessed better encapsulation efficiency (64.10 %) and loading capacity (5.49 µg/mg) for curcumin. In addition, binding with PZ not only improved the thermal, light and digestive stability of curcumin significantly, but lowered its toxic effect on Caco-2 cells and improved relative bioavailability (305 %) compared with that of curcumin only.

Impact of COVID-19 on Subclinical Placental Thrombosis and Maternal Thrombotic Factors.

BACKGROUND: In the context of the SARS-CoV-2 pandemic, our interest was to evaluate the effect of COVID-19 during pregnancy on placenta and coagulation factors. METHODS: a prospective cohort study between January and July 2021 of 55 pregnant women stratified into: Group O, 16 patients with ongoing SARS-CoV-2 infection at delivery; Group R, 21 patients with a history of SARS-CoV-2 infection during pregnancy but who recovered prior to delivery; Group C, 18 control patients with no infection at any time. All women had nasopharyngeal SARS-CoV-2 RT-PCR tests performed within 72 h of delivery. Obstetrical complications were recorded and two physiological inhibitors of coagulation, protein Z (PZ) and dependent protease inhibitor (ZPI), were analyzed in maternal and cord blood. All placentae were analyzed by a pathologist for vascular malperfusion. RESULTS: No patient in any group had a severe COVID-19 infection. More obstetrical complications were observed in Group O (O: n = 6/16 (37%), R: n = 2/21 (10%), C: n = 1/18 (6%), p = 0.03). The incidence of placental vascular malperfusion was similar among the groups (O: n = 9/16 (56%), R: n = 8/21 (42%), C: n = 8/18 (44%), p = 0.68). No PZ or ZPI deficiency was associated with COVID-19. However, an increased ZPI/PZ ratio was observed in neonates of Group R (O: 82.6 (min 41.3-max 743.6), R: 120.7 (29.8-203.5), C: 66.8 (28.2-2043.5), p = 0.04). CONCLUSION: COVID-19 was associated with more obstetrical complications, but not an increased incidence of placental lesions or PZ and ZPI abnormalities.

Heparin activation of protein Z-dependent protease inhibitor (ZPI) allosterically blocks protein Z activation through an extended heparin-binding site.

Protein Z (PZ)-dependent protease inhibitor (ZPI) is a plasma anticoagulant protein of the serpin superfamily, which is activated by its cofactor, PZ, to rapidly inhibit activated factor X (FXa) on a procoagulant membrane surface. ZPI is also activated by heparin to inhibit free FXa at a physiologically significant rate. Here, we show that heparin binding to ZPI antagonizes PZ binding to and activation of ZPI. Virtual docking of heparin to ZPI showed that a heparin-binding site near helix H close to the PZ-binding site as well as a previously mapped site in helix C was both favored. Alanine scanning mutagenesis of the helix H and helix C sites demonstrated that both sites were critical for heparin activation. The binding of heparin chains 72 to 5-saccharides in length to ZPI was similarly effective in antagonizing PZ binding and in inducing tryptophan fluorescence changes in ZPI. Heparin binding to variant ZPIs with either the helix C sites or the helix H sites mutated showed that heparin interaction with the higher affinity helix C site most distant from the PZ-binding site was sufficient to induce these tryptophan fluorescence changes. Together, these findings suggest that heparin binding to a site on ZPI extending from helix C to helix H promotes ZPI inhibition of FXa and allosterically antagonizes PZ binding to ZPI through long-range conformational changes. Heparin antagonism of PZ binding to ZPI may serve to spare limiting PZ and allow PZ and heparin cofactors to target FXa at different sites of action.

Expression and diagnostic value of plasma protein Z and protein Z-dependent protease inhibitor in fetal growth restriction.

OBJECTIVES: Investigating the expression levels of plasma protein Z (PZ) and protein Z-dependent protease inhibitor (ZPI) in fetal growth restriction (FGR) and to explore their diagnostic value in FGR. MATERIAL AND METHODS: In this study, the number of pregnant women with FGR, healthy pregnant women (Healthy Control, HC), and childbearing-age women without pregnancy (Blank Control, BC) is 79, 79, and 60, respectively; their plasma PZ and ZPI levels in each group are determined by ELISAs. Then, the correlations between these indices and FGR were assessed using Spearman analysis. Moreover, these indices' diagnostic values for FGR are evaluated using the receiver operating characteristics (ROC) curves. RESULTS: The plasma levels of PZ and ZPI are significantly decreased in the HC and FGR groups compared against the BC group (P < 0.001), whilst the levels of PZ and ZPI in the FGR groups are lower than those in the HC group (P < 0.01) notably. PZ plasma concentration has positive relationship with ZPI concentrations in the HC and FGR groups. The combination of PZ and ZPI, with the Area under the Curve (AUC) 0.92 (95% CI = 0.88-0.96), the sensitivity 0.82, and the specificity 0.88, outperforms everyone. CONCLUSIONS: Plasma PZ and ZPI are significantly decreased in pregnant women with FGR, which can be used for pregnant women's FGR screening.

Effect of variations in the conserved residues E371 and S359 on the structural dynamics of protein Z dependent protease inhibitor (ZPI): a molecular dynamic simulation study.

Protein Z (PZ) dependent protease inhibitor (ZPI) is a natural anticoagulant inhibiting blood coagulation proteases fXa and fXIa. Despite being a member of the serpin superfamily, it possesses unique structural features such as activation by PZ, regulating its inhibitory function. In order to understand the Reactive Centre Loop (RCL) dynamics of ZPI, which is absolutely critical for its activity, we performed Molecular Dynamics (MD) simulation on ZPI and its E371 and S359 variants located at important conserved functional sites. Unexpectedly, the RCL of E371 variants, (E371K, E371R, and E371Q), were shown to be very stable due to compensatory interactions at the proximal end of RCL. Interestingly, RCL flexibility was shown to be enhanced in the double mutant K318E-E371K due to the repulsive effect of increased negative charge on top of the breach region. Principal component analysis (PCA) coupled with residue wise interaction network analysis(RIN) revealed correlated motion between the RCL and the PZ binding regions in the WT. However, a loss of regulation in correlated motion between RCL and PZ binding hotspot Tyr240 in the double mutant was also observed. Additionally, the S359F and S359I mutations resulted in increased RCL flexibility owing to the disruption of stabilizing hydrogen bonding interaction at the distal end of strand S5A. Thus, the current study proposes that the overall stabilizing interactions of S5A is a major regulator of proper loop movement of ZPI for its activity. The results would be beneficial to engineer activity compromised ZPI as a prophylactic agent for the treatment of hemophilia.Communicated by Ramaswamy H. Sarma.

PROZ May Serve as a Prognostic Biomarker for Early Hepatocellular Carcinoma.

OBJECTIVE: The occurrence and development of hepatocellular carcinoma (HCC) remain unclear. This study aimed to investigate potential diagnostic or prognostic markers for early HCC by applying bioinformatic analysis. METHODS: The gene expression profiles of early HCC and normal tissues from a TCGA dataset were used to identify differentially expressed genes (DEGs) and then analysed by weighted gene coexpression network analysis. The integrated genes were selected to construct the protein-protein interaction (PPI) network and determine the hub genes. The prognostic impact of the hub genes was then analysed. RESULTS: A total of 508 integrated genes were selected from the 615 DEGs and 8956 genes in the turquoise module. A PPI network was constructed, and the top 20 hub genes, including apolipoprotein A-IV (APOA4), fibrinogen gamma chain (FGG), vitamin K-dependent protein Z (PROZ), secreted phosphoprotein 24 (SPP2) and fetuin-B (FETUB), were identified. Only PROZ was significantly associated with the prognosis of early HCC. CONCLUSION: In this study, we demonstrated that the expression of PROZ was decreased in early HCC compared with normal liver controls, and low PROZ expression might result in poor overall survival of early HCC.

Association of Protein Z with Prediabetes and Type 2 Diabetes.

BACKGROUND: Type 2 diabetes mellitus (T2DM) is a progressive metabolic disease. Early detection of prediabetes is important to reduce the risk of T2DM. Some cytokines are known to be associated with T2DM. Therefore, we aimed to identify cytokines as novel biomarkers of glucose dysmetabolism. METHODS: The first stage of the study included 43 subjects (13 subjects with newly diagnosed T2DM, 13 with prediabetes, and 16 with normoglycemia) for cytokine microarray analysis. Blood samples of the subjects were assessed for 310 cytokines to identify potential indicators of prediabetes. The second stage included 142 subjects (36 subjects with T2DM, 35 with prediabetes, and 71 with normoglycemia) to validate the potential cytokines associated with prediabetes. RESULTS: We identified 41 cytokines that differed by 1.5-fold or more in at least one out of the three comparisons (normoglycemia vs. prediabetes, normoglycemia vs. T2DM, and prediabetes vs. T2DM) among 310 cytokines. Finally, we selected protein Z (PROZ) and validated this finding to determine its association with prediabetes. Plasma PROZ levels were found to be decreased in patients with prediabetes (1,490.32±367.19 pg/mL) and T2DM (1,583.34±465.43 pg/mL) compared to those in subjects with normoglycemia (1,864.07±450.83 pg/mL) (P<0.001). There were significantly negative correlations between PROZ and fasting plasma glucose (P=0.001) and hemoglobin A1c (P=0.010). CONCLUSION: PROZ levels were associated with prediabetes and T2DM. We suggest that PROZ may be a promising biomarker for the early detection of prediabetes. Further large-scale studies are needed to evaluate the relationship and mechanism between PROZ and prediabetes and T2DM.

Anti-inflammatory Activity of the Protein Z-Dependent Protease Inhibitor.

The protein Z (PZ)-dependent plasma protease inhibitor (ZPI) is a glycoprotein that inhibits factor XIa and, in the presence of PZ, FXa. Recently, ZPI has been shown to be an acute-phase protein (APP). As usually APPs downregulate the harmful effects of inflammation, we tested whether ZPI could modulate the increase of cytokines observed in inflammatory states. We observed that recombinant human ZPI (rhZPI) significantly decreases the levels of interleukin (IL)-1, IL-6, and tumor necrosis factor- α (TNF-α) induced by lipopolysaccharide (LPS) in a whole blood model. This inhibitory effect was unaffected by the presence of PZ or heparin. A ZPI mutant within the reactive loop center ZPI (Y387A), lacking anticoagulant activity, still had an anti-inflammatory activity. Surprisingly, rhZPI did not inhibit the synthesis of IL-6 or TNF-α when purified monocytes were stimulated by LPS, whereas the inhibitory effect was evidenced when lymphocytes were added to monocytes. The requirement of lymphocytes could be due to the synthesis of CCL5 (RANTES), a chemokine mainly produced by activated lymphocytes which is induced by rhZPI, and which can reduce the production of proinflammatory cytokines in whole blood. Lastly, we observed that the intraperitoneal injection of rhZPI significantly decreased LPS-induced IL-6 and TNF-α production in mouse plasma.

Plasma concentration of protein Z-dependent protease inhibitor and ZPI exon 3 mutations in preeclampsia.

Protein Z-dependent protease inhibitor (ZPI) serves as a cofactor of inhibition of FXa and FXIa by protein Z. The levels of protein Z and polymorphisms have been shown in preeclampsia (PE) patients, but the plasma levels of ZPI and ZPI gene mutations were not reported yet. The principal aim of this study was to identify the concentration of ZPI and gene polymorphism in PE. ZPI levels were determined in 113 PE patients (age: 29.9 ± 3.9 years) and in 106 controls (normal pregnancy, age: 27.0 ± 2.8 years). ZPI was measured by enzyme-linked immunosorbent assay kit, and the gene polymorphism was determined by polymerase chain reaction and sequencing. The results showed ZPI antigen was found to be significantly lower in PE patients than in controls (ZPI, 1.24 ± 0.29 mg/L vs. 1.94 ± 0.35 mg/L, p < 0.05). The exon-3 missense mutations were distributed in patients and controls and there was no convincing correlation between these mutations and PE. It was of interest to observe a close relationship between the genotypes of the exon 3 polymorphisms 181 A > G and 481 A > T in the ZPI gene.Impact statementWhat is already known on this subject? The occurrence of PE is closely related to dysfunction of coagulation, and it is known that the decrease of PZ level can increase the occurrence probability of PE, while the polymorphism of PZ is not related to the occurrence of PE. As a cofactor of PZ, the content and polymorphism of ZPI which related to the occurrence of PE is worth further study.What the results of this study add? ZPI antigen was found to be significantly lower in PE patients than in controls, but there was no convincing correlation between exon-3 mutations and PE.What the implications are of these findings for clinical practice and/or further research? Our results support the view that ZPI plays a significant role in anticoagulant, and the genotype of the 181 gene polymorphism in exon-3 and 481 gene polymorphism in exon-3 are closely related. Other mutations like 435T > G(Phe145Leu), 972G > A(Trp324X), 1151A > G(Gln384Arg) are necessary to confirm the association between ZPI and prothrombotic state including PE.

Distinct Molecular Mechanisms of Host Immune Response Modulation by Arenavirus NP and Z Proteins.

Endemic to West Africa and South America, mammalian arenaviruses can cross the species barrier from their natural rodent hosts to humans, resulting in illnesses ranging from mild flu-like syndromes to severe and fatal haemorrhagic zoonoses. The increased frequency of outbreaks and associated high fatality rates of the most prevalent arenavirus, Lassa, in West African countries, highlights the significant risk to public health and to the socio-economic development of affected countries. The devastating impact of these viruses is further exacerbated by the lack of approved vaccines and effective treatments. Differential immune responses to arenavirus infections that can lead to either clearance or rapid, widespread and uncontrolled viral dissemination are modulated by the arenavirus multifunctional proteins, NP and Z. These two proteins control the antiviral response to infection by targeting multiple cellular pathways; and thus, represent attractive targets for antiviral development to counteract infection. The interplay between the host immune responses and viral replication is a key determinant of virus pathogenicity and disease outcome. In this review, we examine the current understanding of host immune defenses against arenavirus infections and summarise the host protein interactions of NP and Z and the mechanisms that govern immune evasion strategies.