The two faces of interleukin 12: a pro-inflammatory cytokine and a key immunoregulatory molecule produced by antigen-presenting cells

Both Full-Length and Protease-Cleaved Products of Osteopontin Are Elevated in Infectious Diseases

Circulating full-length osteopontin (FL-OPN) is elevated in plasma from patients with various infectious diseases, such as adult T-cell leukemia, Mycobacterium tuberculosis (TB), hepatitis virus infection, leptospirosis, acquired immune deficiency syndrome (AIDS), AIDS/TB, and coronavirus disease 2019 (COVID-19). Proteolysis of OPN by thrombin, matrix metalloproteases, caspase 8/3, cathepsin D, plasmin, and enterokinase generates various cleaved OPNs with a variety of bioactivities by binding to different target cells. Moreover, OPN is susceptible to gradual proteolysis. During inflammation, one of the cleaved fragments, N-terminal thrombin-cleaved OPN (trOPN or OPN-Arg¹⁶⁸ [OPN-R]), induces dendritic cell (DC) adhesion. Further cleavage by carboxypeptidase B2 or carboxypeptidase N removes Arg¹⁶⁸ from OPN-R to OPN-Leu¹⁶⁷ (OPN-L). Consequently, OPN-L decreases DC adhesion. In particular, the differences in plasma level over time are observed between FL-OPN and its cleaved OPNs during inflammation. We found that the undefined OPN levels (mixture of FL-OPN and cleaved OPN) were elevated in plasma and reflected the pathology of TB and COVID-19 rather than FL-OPN. These infections are associated with elevated levels of various proteases. Inhibition of the cleavage or the activities of cleaved products may improve the outcome of the therapy. Research on the metabolism of OPN is expected to create new therapies against infectious diseases.

The Pseudomonas aeruginosa Mannose Sensitive Hamemagglutination Strain (PA-MSHA) Induces a Th1-Polarizing Phenotype by Promoting Human Dendritic Cells Maturation

Pseudomonas aeruginosa mannose sensitive hamemagglutination strain (PA-MSHA) is a kind of peritrichous P. aeruginosa strain with MSHA fimbriae and has been shown to activate kinds of immunocytes. Dendritic cells (DCs) are specialized antigen-presenting cells required for the stimulating and priming CD4(+) T cells toward the T helper cell type 1 (Th1), Th2 and other different phenotypes. PA-MSHA effecting on Th1 remains an important missing link. Here we demonstrated that PA-MSHA augmented monocytes derived-dendritic cells (Mo-DCs) expression of HLA-DR, co-stimulatory and adhesion molecules, and induced Th1-promoting interleukin-12 and tumor necrosis factor α secretion, in addition, PA-MSHA treated Mo-DCs displayed lesser endocytic capacity. Furthermore, in mixed lymphocyte reactions, allostimulatory capacity of Mo-DCs was enhanced by PA-MSHA, CD4(+) T cells stimulated by PA-MSHA -activated Mo-DCs showed a Th1-polarized cytokine production, increasing secretion of IFN-γ and decreasing secretion of IL-10 and IL-4. Our findings identified PA-MSHA as an important exogenous factor that induced DCs maturation toward a Th1-promoting phenotype.

Positive selection of mC46-expressing CD4+ T cells and maintenance of virus specific immunity in a primate AIDS model

Despite continued progress in the development of novel antiretroviral therapies, it has become increasingly evident that drug-based treatments will not lead to a functional or sterilizing cure for HIV(+) patients. In 2009, an HIV(+) patient was effectively cured of HIV following allogeneic transplantation of hematopoietic stem cells (HSCs) from a CCR5(-/-) donor. The utility of this approach, however, is severely limited because of the difficulty in finding matched donors. Hence, we studied the potential of HIV-resistant stem cells in the autologous setting in a nonhuman primate AIDS model and incorporated a fusion inhibitor (mC46) as the means for developing infection-resistant cells. Pigtail macaques underwent identical transplants and Simian-Human Immunodeficiency Virus (SHIV) challenge procedures with the only variation between control and mC46 macaques being the inclusion of a fusion-inhibitor expression cassette. Following SHIV challenge, mC46 macaques, but not control macaques, showed a positive selection of gene-modified CD4(+) T cells in peripheral blood, gastrointestinal tract, and lymph nodes, accounting for >90% of the total CD4(+) T-cell population. mC46 macaques also maintained high frequencies of SHIV-specific, gene-modified CD4(+) T cells, an increase in nonmodified CD4(+) T cells, enhanced cytotoxic T lymphocyte function, and antibody responses. These data suggest that HSC protection may be a potential alternative to conventional antiretroviral therapy in patients with HIV/AIDS.

Candida and invasive candidiasis: back to basics

The ubiquitous Candida spp. is an opportunistic fungal pathogen which, despite treatment with antifungal drugs, can cause fatal bloodstream infections (BSIs) in immunocompromised and immunodeficient persons. Thus far, several major C. albicans virulence factors have been relatively well studied, including morphology switching and secreted degradative enzymes. However, the exact mechanism of Candida pathogenesis and the host response to invasion are still not well elucidated. The relatively recent discovery of the quorum-sensing molecule farnesol and the existence of quorum sensing as a basic regulatory phenomenon of the C. albicans population behavior has revolutionized Candida research. Through population density regulation, the quorum-sensing mechanism also controls the cellular morphology of a C. albicans population in response to environmental factors, thereby, effectively placing morphology switching downstream of quorum sensing. Thus, the quorum-sensing phenomenon has been hailed as the 'missing piece' of the pathogenicity puzzle. Here, we review what is known about Candida spp. as the etiological agents of invasive candidiasis and address our current understanding of the quorum-sensing phenomenon in relation to virulence in the host.

Differentiation and immune function of human dendritic cells following infection by respiratory syncytial virus

RSV causes annual epidemics of bronchiolitis in winter months resulting in the hospitalization of many infants and the elderly. Dendritic cells (DCs) play a pivotal role in coordinating immune responses to infection and some viruses skew, or subvert, the immune functions of DCs. RSV infection of DCs could alter their function and this could explain why protection after natural RSV infection is incomplete and of short duration. In this study, this interaction between DCs and RSV was investigated using a human primary culture model. DCs were generated from purified healthy adult volunteer peripheral blood monocytes. Effects of RSV upon DC phenotype with RSV primed DCs was measured using flow cytometry. Changes to viability and proliferation of cocultured DCs and T-cells were determined using microscopy with fluorescent dyes (Hoechst 33342 and propidium iodide). DC maturation was not prevented by the RSV challenge. RSV infected a fraction of DCs (10-30%) but the virus replicated slowly in these cells with only small reduction to cell viability. DCs challenged with RSV stimulated T-cell proliferation less well than lipopolysaccharide. This is the first study to demonstrate RSV infection of human monocyte derived DCs and suggests that the virus does not significantly interfere with the function of these cells and potentially may promote cellular rather than humoral responses.

Osteopontin functionally activates dendritic cells and induces their differentiation toward a Th1-polarizing phenotype

Osteopontin (OPN) has been shown to have T helper 1 (Th1) cytokine functions in cell-mediated immunity. Deficiency of OPN is linked to a reduced Th1 immune response in autoimmunity, infectious disease, and delayed-type allergy. Dendritic cells (DCs) are central for the induction of T-cell-mediated immunity, when initially flexible DCs are instructed by priming signals and tissue-derived factors to adopt Th1, Th2, or regulatory T-cell-inducing phenotypes. Although OPN influences the cytokine secretion of T cells and macrophages, its effects on DC polarization remain an important missing link in the understanding of OPN functions in Th1 immunity. Here we demonstrate that OPN promotes the emigration of human DCs from the epidermis and functionally activates myeloid-type DCs, augmenting their expression of HLA-DR, costimulatory, and adhesion molecules. OPN induces their Th1-promoting tumor necrosis factor alpha (TNF-alpha) and interleukin-12 (IL-12) secretion, and enhances their allostimulatory capacity. In mixed lymphocyte reactions (MLRs), OPN stimulates IL-12 secretion by DCs, inducing elevated interferon-gamma (IFN-gamma) production by T cells. Naive Th cells stimulated by OPN-activated DCs show a Th1-polarized cytokine production. Our findings identify OPN as an important tissue-derived factor that DCs encounter when traveling from peripheral sites of activation to secondary lymphatic organs, which induces DC maturation toward a Th1-promoting phenotype.

Feedback mechanisms between T helper cells and macrophages in the determination of the immune response

The interactions between macrophages and T helper (Th) cells are a complex interplay of positive and negative signals. Some of the mathematical models of interactions between T helpers have indeed taken the influence of macrophages into account. In this work the macrophage is not considered as an extrinsic agent, that is duly directed by the T cells to be cytotoxic, nor is there consideration of T helper cell populations that are dominantly regulated by extrinsic properties of antigens per se, or by certain classes of presenting cells that preferentially select certain classes of lymphocytes or bias their commitment. Rather, a simplified model of feedback loops between Th cells and macrophages is formulated and analyzed. It is suggested how the mutual influence between Th and macrophages can determine the cytokine secretion pattern of these populations. The model provides a feedback scenario to account for experimental findings concerning reversal in the dominance of a specific cytokine profile in the course of some infections. A possible scenario accounting for the difference between the stability of Th1 and Th2 cytokine pattern is put forward. The model suggests explanations for the variability in the outcome of the immune response according to different body compartments. A rationale is presented that accounts for paradoxical findings indicating that Th1 cytokines are sometimes responsible for the downregulation of a Th1 dominated response.

Signalling through NK1.1 triggers NK cells to die but induces NK T cells to produce interleukin-4

In vivo inoculation of specific antibody is an accepted protocol for elimination of specific cell populations. Except for anti-CD3 and anti-CD4, it is not known if the depleted cells are eliminated by signalling through the target molecule or through a more non-specific mechanism. C57BL/6 mice were inoculated with anti-natural killer (NK1.1) monoclonal antibody (mAb). Thereafter spleen cells were harvested, stained for both surface and intracellular markers, and analysed by flow cytometry. As early as 2 hr post inoculation, NK cells were signalled to become apoptotic while signalling through the NK1.1 molecule activated NK1.1+ T-cell receptor (TCR)+ (NK T) cells to increase in number, and produce interleukin-4 (IL-4). Anti NK1.1 mAb was less efficient at signalling apoptosis in NK cells when NK T-cell deficient [beta 2-microglobulin beta 2m-deficient] mice were used compared with wild type mice. Efficient apoptotic signalling was restored when beta 2m-deficient mice were reconstituted with NK T cells. NK-specific antibody best signals the apoptotic process in susceptible NK cells when resistant NK T cells are present, activated, and secrete IL-4.