Immune Responses to Middle East Respiratory Syndrome Coronavirus During the Acute and Convalescent Phases of Human Infection.

BACKGROUND: An understanding of immune responses against the Middle East respiratory syndrome (MERS) is important for the development of treatments and preventive measures. Here, we investigated the spectrum of immune responses occurring in patients with MERS during the early period of infection. METHODS: We obtained peripheral blood samples from 27 hospitalized patients recruited during the epidemic that occurred in 2015 in South Korea. Plasma cytokines/chemokines and antibodies were quantified. Virus-specific T cells were examined by intracellular cytokine staining after stimulation of peripheral blood mononuclear cells with overlapping peptides spanning whole virus structural proteins. RESULTS: At the acute phase of infection, elevated levels of plasma proinflammatory cytokines/chemokines were detected in proportion to the severity of the disease. Distinctively high frequencies of MERS coronavirus-reactive CD8+ T cells were also observed in patients with severe/moderate illness, whereas antibody and CD4+ T-cell responses were minimally detected at this stage. At the convalescent phase, disease severity-dependent antibody responses emerged and antigen-reactive cells were identified in both T-cell subsets. These T cells belonged to the T-helper 1 or type 1 cytotoxic T cell subtypes. While CD8+ T cells responded preferentially to the viral S protein compared with E/M/N proteins, especially at the acute stage, slightly more CD4+ T cells recognized E/M/N proteins compared with S protein at the convalescent phase. CONCLUSIONS: Our findings show an association between the early CD8+ T-cell response and the severity of the infection, and also provide basic information that may help to prepare effective control strategies for MERS in humans.

Differential expression of CD57 in antigen-reactive CD4+ T cells between active and latent tuberculosis infection.

The development of diagnostic tests that predict the progression of latent tuberculosis infection to active disease is pivotal for the eradication of tuberculosis. As an initial step to achieve this goal, our study's aim was to identify biomarkers that differentiate active from latent tuberculosis infection. We compared active and latent tuberculosis infection groups in terms of the precursor frequency, functional subset differentiation, and senescence/exhaustion surface marker expression of antigen-specific CD4(+) T cells, which were defined as dividing cells upon their encountering with Mycobacterium (M.) tuberculosis antigens. Among several parameters shown to have statistically significant differences between the two groups, the frequency of CD57-expressing cells could differentiate effectively between active disease and latent infection. Our results suggest that the expression of CD57 in M. tuberculosis-reactive CD4(+) T cells could be a promising candidate biomarker with which to identify individuals with latent tuberculosis infection prone to progression to active disease.

Immune parameters differentiating active from latent tuberculosis infection in humans.

Tuberculosis remains a highly prevalent infectious disease worldwide. Identification of the immune parameters that differentiate active disease from latent infection will facilitate the development of efficient control measures as well as new diagnostic modalities for tuberculosis. Here, we investigated the cytokine production profiles of monocytes and CD4(+) T lymphocytes upon encountering mycobacterial antigens. In addition, cytokines and lipid mediators with immune-modulating activities were examined in plasma samples ex vivo. Comparison of these parameters in active tuberculosis patients and healthy subjects with latent infection revealed that, active tuberculosis was associated with diminished Th1-type cytokine secretion from CD4(+) T cells and less augmented inflammatory cytokine secretion from monocytes induced by IFN-γ than that in latent tuberculosis infection. In addition, a higher plasma concentration of lipoxin A4 and lower ratio of prostaglandin E2 to lipoxin A4 were observed in active cases than in latent infections. These findings have implications for preparing new therapeutic strategies and for differential diagnosis of the two types of tuberculosis infection.

Analysis of cepA encoding an efflux pump-like protein in Corynebacterium glutamicum.

A gene encoding a homolog of purine efflux proteins of Escherichia coli and Bacillus subtilis was identified in the genome of Corynebacterium glutamicum and designated as cepA. The gene encoded a putative protein product, containing 12 transmembrane helixes, which is a typical feature of integral membrane transport proteins. To elucidate the function of the gene, we constructed a cepA deletion mutant (ΔcepA) and a cepA-overexpressing strain and analyzed their physiological characteristics. The cepA gene could be deleted with no critical effect on cell growth. However, the cell yield of a ΔcepA strain was decreased by 10% as compared to that of a strain carrying a cepA-overexpression plasmid (P180-cepA). Further analysis identified increased resistance of the P180-cepA strain to the purine analogues 6-mercaptopurine and 6-mercaptoguanine, but not to 2-aminopurine and purine nucleoside analogues. Moreover, this strain showed increased resistance to the antibiotics nalidixic acid and ampicillin. Collectively, these data suggest that cepA is a novel multidrug resistance gene and probably functions in the efflux of toxic substances from the inside of cells to the environment, thus allowing cells to reach a higher cell yield.

Characteristics of methionine production by an engineered Corynebacterium glutamicum strain.

A methionine-producing strain was derived from a lysine-producing Corynebacterium glutamicum through a process of genetic manipulation in order to assess its potential to synthesize and accumulate methionine during growth. The strain carries a deregulated hom gene (hom(FBR)) to abolish feedback inhibition of homoserine dehydrogenase by threonine and a deletion of the thrB gene (delta thrB) to abolish threonine synthesis. The constructed C. glutamicum MH20-22B/hom(FBR)/delta thrB strain accumulated 2.9 g/l of methionine by batch fermentation and showed resistance to methionine analogue ethionine at concentrations up to 30 mM. The growth of the strain was apparently impaired as a result of the accumulation of methionine biosynthetic intermediate, homocysteine. Production assays also revealed that the accumulation of methionine in the growth medium was transient and declined as the carbon source was depleted. During the period of methionine disappearance, the methionine biosynthetic genes were completely repressed in the engineered strains but not in the parental strain. After all, we have not only successfully constructed a methionine-producing C. glutamicum strain by genetic manipulation, but also revealed cellular constraints in attaining high yield and productivity.