Exploiting immunotherapy in Mycobacterium tuberculosis-infected mice: sphingosine 1-phosphate treatment results in a protective or detrimental effect depending on the stage of infection

Battling COVID-19 Pandemic: Sphingosine-1-Phosphate Analogs as an Adjunctive Therapy?

With the sudden outbreak of COVID-19 patient worldwide and associated mortality, it is critical to come up with an effective treatment against SARS-CoV-2. Studies suggest that mortality due to COVID 19 is mainly attributed to the hyper inflammatory response leading to cytokine storm and ARDS in infected patients. Sphingosine-1-phosphate receptor 1 (S1PR1) analogs, AAL-R and RP-002, have earlier provided in-vivo protection from the pathophysiological response during H1N1 influenza infection and improved mortality. Recently, it was shown that the treatment with sphingosine-1-phosphate receptor 1 analog, CYM5442, resulted in the significant dampening of the immune response upon H1N1 challenge in mice and improved survival of H1N1 infected mice in combination with an antiviral drug, oseltamivir. Hence, here we suggest to investigate the possible utility of using S1P analogs to treat COVID-19.

Peptidoglycan Recognition Protein 4 Suppresses Early Inflammatory Responses to Bordetella pertussis and Contributes to Sphingosine-1-Phosphate Receptor Agonist-Mediated Disease Attenuation

Incidence of whooping cough (pertussis), a bacterial infection of the respiratory tract caused by the bacterium Bordetella pertussis, has reached levels not seen since the 1950s. Antibiotics fail to improve the course of disease unless administered early in infection. Therefore, there is an urgent need for the development of antipertussis therapeutics. Sphingosine-1-phosphate receptor (S1PR) agonists have been shown to reduce pulmonary inflammation during Bordetella pertussis infection in mouse models. However, the mechanisms by which S1PR agonists attenuate pertussis disease are unknown. We report the results of a transcriptome sequencing study examining pulmonary transcriptional responses in B. pertussis-infected mice treated with S1PR agonist AAL-R or vehicle control. This study identified peptidoglycan recognition protein 4 (PGLYRP4) as one of the most highly upregulated genes in the lungs of infected mice following S1PR agonism. PGLYRP4, a secreted, innate mediator of host defenses, was found to limit early inflammatory pathology in knockout mouse studies. Further, S1PR agonist AAL-R failed to attenuate pertussis disease in PGLYRP4 knockout (KO) mice. B. pertussis virulence factor tracheal cytotoxin (TCT), a secreted peptidoglycan breakdown product, induces host tissue damage. TCT-oversecreting strains were found to drive an early inflammatory response similar to that observed in PGLYRP4 KO mice. Further, TCT-oversecreting strains induced significantly greater pathology in PGLYRP4-deficient animals than their wild-type counterparts. Together, these data indicate that S1PR agonist-mediated protection against pertussis disease is PGLYRP4 dependent. Our data suggest PGLYRP4 functions, in part, by preventing TCT-induced airway damage.

The Multirole of Liposomes in Therapy and Prevention of Infectious Diseases

Liposomes are closed bilayer structures spontaneously formed by hydrated phospholipids that are widely used as efficient delivery systems for drugs or antigens, due to their capability to encapsulate bioactive hydrophilic, amphipathic, and lipophilic molecules into inner water phase or within lipid leaflets. The efficacy of liposomes as drug or antigen carriers has been improved in the last years to ameliorate pharmacokinetics and capacity to release their cargo in selected target organs or cells. Moreover, different formulations and variations in liposome composition have been often proposed to include immunostimulatory molecules, ligands for specific receptors, or stimuli responsive compounds. Intriguingly, independent research has unveiled the capacity of several phospholipids to play critical roles as intracellular messengers in modulating both innate and adaptive immune responses through various mechanisms, including (i) activation of different antimicrobial enzymatic pathways, (ii) driving the fusion–fission events between endosomes with direct consequences to phagosome maturation and/or to antigen presentation pathway, and (iii) modulation of the inflammatory response. These features can be exploited by including selected bioactive phospholipids in the bilayer scaffold of liposomes. This would represent an important step forward since drug or antigen carrying liposomes could be engineered to simultaneously activate different signal transduction pathways and target specific cells or tissues to induce antigen-specific T and/or B cell response. This lipid-based host-directed strategy can provide a focused antimicrobial innate and adaptive immune response against specific pathogens and offer a novel prophylactic or therapeutic option against chronic, recurrent, or drug-resistant infections.

Lysophosphatidic acid enhances antimycobacterial response during in vivo primary Mycobacterium tuberculosis infection

Lysophospholipids may play an important protective role during primary infection of Mycobacterium tuberculosis (MTB) by enhancing innate antimycobacterial immune response of both macrophages and alveolar epithelial cells. Here, we show that treatment with lysophosphatidic acid (LPA) of mice aerogenically infected with MTB immediately after infection results in a significant early reduction of pulmonary CFUs and of histopathological damage in comparison with control mice. In contrast, treatment of acute disease does not result in any improvement of both microbiological and histopathological parameters. Altogether, these results show that LPA treatment can exert protective effect if administrated during primary infection, only.

Role of sphingosine-1-phosphate (S1P) and S1P receptor 2 in the phagocytosis of Cryptococcus neoformans by alveolar macrophages

The pathogenic fungus Cryptococcus neoformans is a major cause of morbidity and mortality in immunocompromised individuals. Infection of the human host occurs through inhalation of infectious propagules following environmental exposure. In the lung, C. neoformans can reside in the extracellular environment of the alveolar spaces or, upon phagocytosis, it can survive and grow intracellularly within alveolar macrophages (AMs). In previous studies, we found that sphingosine kinase 1 (SK1) influenced the intracellular residency of C. neoformans within AMs. Therefore, with this study we aimed to examine the role of the SK1 lipid product, sphingosine-1-phosphate (S1P), in the AMs-C. neoformans interaction. It was found that extracellular S1P enhances the phagocytosis of C. neoformans by AMs. Using both genetic and pharmacological approaches we further show that extracellular S1P exerts its effect on the phagocytosis of C. neoformans by AMs through S1P receptor 2 (S1P2). Interestingly, loss of S1P2 caused a dramatic decrease in the mRNA levels of Fcγ receptors I (FcγRI), -II and -III. In conclusion, our data suggest that extracellular S1P increases antibody-mediated phagocytosis through S1P2 by regulating the expression of the phagocytic Fcγ receptors.

Role of host sphingosine kinase 1 in the lung response against Cryptococcosis

Cryptococcus neoformans is a fungal pathogen causing pulmonary infection and a life-threatening meningoencephalitis in human hosts. The fungus infects the host through inhalation, and thus, the host response in the lung environment is crucial for containment or dissemination of C. neoformans to other organs. In the lung, alveolar macrophages (AMs) are key players in the host lung immune response, and upon phagocytosis, they can kill C. neoformans by evoking an effective immune response through a variety of signaling molecules. On the other hand, under conditions not yet fully defined, the fungus is able to survive and proliferate within macrophages. Since the host sphingosine kinase 1 (SK1) regulates many signaling functions of immune cells, particularly in macrophages, in this study we determined the role of SK1 in the host response to C. neoformans infection. Using wild-type (SK1/2(+/+)) and SK1-deficient (SK1(-/-)) mice, we found that SK1 is dispensable during infection with a facultative intracellular wild-type C. neoformans strain. However, SK1 is required to form a host lung granuloma and to prevent brain infection by a C. neoformans mutant strain lacking the cell wall-associated glycosphingolipid glucosylceramide (Delta gcs1), previously characterized as a mutant able to replicate only intracellularly. Specifically, in contrast to those from SK1/2(+/+) mice, lungs from SK1(-/-) mice have no collagen deposition upon infection with C. neoformans Delta gcs1, and AMs from these mice contain significantly more C. neoformans cells than AMs from SK1/2(+/+) mice, suggesting that under conditions in which C. neoformans is more internalized by AMs, SK1 may become important to control C. neoformans infection. Indeed, when we induced immunosuppression, a host condition in which wild-type C. neoformans cells are increasingly found intracellularly, SK1(-/-) survived significantly less than SK1/2(+/+) mice infected with a facultative intracellular wild-type strain, suggesting that SK1 has an important role in controlling C. neoformans infection under conditions in which the fungus is predominantly found intracellularly.