Macrophage fate: to kill or not to kill?

Macrophages are dynamic innate immune cells that either reside in tissue, serving as sentinels, or recruited as monocytes from bone marrow into inflamed and infected tissue. In response to cues in the tissue microenvironment (TME), macrophages polarize on a continuum toward M1 or M2 with diverse roles in progression and resolution of disease. M1-like macrophages exhibit proinflammatory functions with antimicrobial and anti-tumorigenic activities, while M2-like macrophages have anti-inflammatory functions that generally resolve inflammatory responses and orchestrate a tissue healing process. Given these opposite phenotypes, proper spatiotemporal coordination of macrophage polarization in response to cues within the TME is critical to effectively resolve infectious disease and regulate wound healing. However, if this spatiotemporal coordination becomes disrupted due to persistent infection or dysregulated coagulation, macrophages' inappropriate response to these cues will result in the development of diseases with clinically unfavorable outcomes. Since plasticity and heterogeneity are hallmarks of macrophages, they are attractive targets for therapies to reprogram toward specific phenotypes that could resolve disease and favor clinical prognosis. In this review, we discuss how basic science studies have elucidated macrophage polarization mechanisms in TMEs during infections and inflammation, particularly coagulation. Therefore, understanding the dynamics of macrophage polarization within TMEs in diseases is important in further development of targeted therapies.

2B4 (CD244, SLAMF4) and CS1 (CD319, SLAMF7) in systemic lupus erythematosus and cancer.

Signaling Lymphocyte Activation Molecule (SLAM) family receptors are expressed on different types of hematopoietic cells and play important role in immune regulation in health and disease. 2B4 (CD244, SLAMF4) and CS1 (CD319, CRACC, SLAMF7) were originally identified as NK cell receptors regulating NK cell cytolytic activity. 2B4 is expressed on all NK cells, a subpopulation of T cells, monocytes and basophils. Unlike other activating and inhibitory receptors, 2B4 (CD244) interaction with its ligand CD48 has been shown to mediate both activating and inhibitory functions. Defective signaling via 2B4 due to mutations in signaling adaptor SAP contributes to X-linked lymphoproliferative Disease (XLP). Expression of 2B4 and CS1 are altered in systemic lupus erythematosus (SLE). CS1 is overexpressed in multiple myeloma (MM) and anti-CS1 mab (Elotuzumab/Empliciti) has been approved by FDA as a breakthrough drug for treatment for MM patients. CAR -T cells or CAR- NK cells containing full length CS1 or the signaling domain of 2B4 with TCR-ζ have shown promising results to treat cancer and autoimmune diseases.

Lack of an atypical PDR transporter generates an immunogenic Cryptococcus neoformans strain that drives a dysregulated and lethal immune response in murine lungs.

Cryptococcus neoformans is an opportunistic fungal pathogen responsible for >150,000 deaths every year with a mortality rate as high as 81%. This high medical burden is due, in part, to an incomplete understanding of its pathogenesis. In a previous study, we identified a cryptococcal atypical pleiotropic drug resistance (PDR) transporter, PDR6, that regulated antifungal resistance and host interactions. Here, we follow-up on the role of PDR6 in cryptococcal virulence. In vivo, mice infected with the pdr6Δ strain display altered symptomatology and disease progression. Specifically, we observed a significant increase in the innate immune cell populations in the pdr6Δ-infected mice when compared to their WT-infected littermates. Furthermore, quantification of pulmonary cytokines/chemokines revealed a robust increase of pro-inflammatory cytokines in mice infected with the pdr6Δ mutant strain. Whereas antifungal treatment of pdr6Δ-infected animals did not affect survival, treatment with a corticosteroid significantly extended survival, highlighting the importance of a balanced/controlled host immune response. We determined that the hyper-inflammatory immune response occurs, in part, because the loss of the Pdr6 transporter indirectly alters the cryptococcal cell wall architecture and results in the increased exposure of chitin, ß-glucan, and other cryptococcal-specific pathogen associated molecular patterns. Taken together, this study provides clinical insights regarding cryptococcal pathogenesis while also providing additional functions of PDR-type ATP-binding cassette (ABC) transporters in pathogenic fungi.

The catheterized bladder environment induces dysregulation of macrophage polarization exacerbating bacterial UTI.

Urinary catheterization causes bladder damage, predisposing hosts to catheter-associated urinary tract infections (CAUTIs). CAUTI pathogenesis is mediated by bladder damage-induced inflammation, resulting in accumulation and deposition of the blood-clotting protein fibrinogen (Fg) and its matrix form fibrin, which are exploited by uropathogens as biofilm platforms to establish infection. Catheter-induced inflammation also results in robust immune cell recruitment, including macrophages (Mϕs). A fundamental knowledge gap is understanding the mechanisms by which the catheterized-bladder environment suppresses the Mϕ antimicrobial response, allowing uropathogen persistence. Here, we found that Fg and fibrin differentially modulate M1 and M2 Mϕ polarization, respectively. We unveiled that fibrin accumulation in catheterized mice induced an anti-inflammatory M2-like Mϕ phenotype, correlating with pathogen persistence. Even GM-CSF treatment of wildtype mice to promote M1 polarization was not sufficient to reduce bacterial burden and dissemination, indicating that the catheterized-bladder environment provides mixed signals, dysregulating Mϕ polarization, hindering its antimicrobial response against uropathogens.

Blocking PCNA interaction with NKp44 enhances primary natural killer cell-mediated lysis of triple-negative breast cancer cells.

Among the innate immune cells, natural killer cells (NK) serve its role in cytolytic targeting against infected and cancerous cells. NK function is regulated by an intricate balance of signals from interactions between activating and inhibitory NK receptors and ligands expressed on target cells. As an immune evasion strategy, cancer cells, particularly triple-negative breast cancer cells (TNBCs), express ligands that interact with NK receptors to inhibit NK cell cytolytic function. Our studies have revealed that Proliferating Cell Nuclear Antigen (PCNA), normally expressed in the nucleus with DNA replication and repair roles, was present on the cell surface of TNBC cell lines MDA-MB-231, -436, and -468. To elucidate the function of cell surface PCNA, we blocked PCNA on TNBCs with antibodies which both disrupted interaction with NKp44 and enhanced lysis by primary NK cells. Furthermore, a combinational antibody treatment of TNBCs with α-LLT1 and α-PCNA antibodies augments NK-mediated lysis. These results together suggest that cell surface PCNA on TNBCs enables evasion from cytolytic killing by NK cells. Blocking PCNA-NKp44 interaction with antibodies may potentially open an additional avenue in treatment of TNBCs.

Complete Genome Sequence of Salmonella enterica Serovar Heidelberg Siphophage Sepoy.

Phage Sepoy infects Salmonella enterica serovar Heidelberg, a Gram-negative bacterium that causes severe foodborne illnesses. Bacteriophages infecting this pathogen may be used as biocontrol agents for preventing Salmonella foodborne diseases. Here, we present the complete genome sequence of Sepoy, a T5-like siphophage.

Blocking LLT1 (CLEC2D, OCIL)-NKRP1A (CD161) interaction enhances natural killer cell-mediated lysis of triple-negative breast cancer cells.

Triple-negative breast cancer (TNBC) is the most invasive form of breast cancer due to an absence of estrogen (ER), progesterone (PR), and human epidermal growth factor-2 (HER2) receptors on the cell surface. TNBC accounts for approximately 12 to 20 percent of all breast cancer cases. The absence of ER, PR, and HER2 receptors on TNBCs and its ability to develop drug resistance renders it difficult to eradicate or retrogress tumor growth with hormonal therapy and chemotherapy. Triple-negative breast cancer is associated with poorer prognosis, increased chance of relapse, and lower chance of survival. Patients with TNBC have poorer outcome to conventional treatments than patients with other types of breast cancer. Natural killer cell-mediated immunotherapy is a promising therapeutic option for patients with TNBC. Natural killer cells contribute to the immune system by recognizing tumor cells through interactions between ligands on tumor cells and natural killer cell receptors. NK cell function is regulated by a net balance of signals from activating and inhibitory receptors interacting with ligands on target cells. Lectin-like Transcript-1 (LLT1, CLEC2D, OCIL) is a ligand that interacts with NK cell receptor NKRP1A (CD161) and inhibits NK cell activation. In this study, we have identified expression of LLT1 on TNBC cell lines MDA-MB-231 and MDA-MB-436 through flow cytometry, western blot, and confocal microscopy. We have demonstrated that blocking LLT1 on TNBCs with antibodies disrupts interaction with NKRP1A and enhances lysis of TNBCs by primary natural killer cells. We have also shown that a gene knockdown of LLT1 decreases cell surface expression of LLT1 on TNBCs and increases NK cell-mediated lysis of these TNBCs. The results suggest that LLT1 on TNBCs function as a method of evasion from immunosurveillance by NK cells. Blocking LLT1-NKRP1A interaction activates lysis by NK cells and will potentially open a new immunotherapeutic strategy for treatment of TNBC.