Type I IFN, Ly6C+ cells, and Phagocytes Support Suppression of Peritoneal Carcinomatosis Elicited by a TLR and CLR Agonist Combination

Type I IFN Receptor Signaling on B Cells Promotes Antibody Responses to Polysaccharide Antigens

We previously reported monophosphoryl lipid A (MPL) and synthetic cord factor trehalose-6,6'-dicorynomycolate (TDCM) significantly increase Ab responses to T cell-independent type 2 Ags (TI-2 Ags) in a manner dependent on B cell-intrinsic TLR4 expression, as well as MyD88 and TRIF proteins. Given the capacity of MPL to drive type I IFN production, we aimed to investigate the extent to which type I IFN receptor (IFNAR) signaling was required for TI-2 responses and adjuvant effects. Using Ifnar1-/- mice and IFNAR1 Ab blockade, we found that IFNAR signaling is required for optimal early B cell activation, expansion, and Ab responses to nonadjuvanted TI-2 Ags, including the pneumococcal vaccine. Further study demonstrated that B cell-intrinsic type I IFN signaling on B cells was essential for normal TI-2 Ab responses. In particular, TI-2 Ag-specific B-1b cell activation and expansion were significantly impaired in Ifnar1-/- mice; moreover, IFNAR1 Ab blockade similarly reduced activation, expansion, and differentiation of IFNAR1-sufficient B-1b cells in Ifnar1-/- recipient mice, indicating that B-1b cell-expressed IFNAR supports TI-2 Ab responses. Consistent with these findings, type I IFN significantly increased the survival of TI-2 Ag-activated B-1b cells ex vivo and promoted plasmablast differentiation. Nonetheless, MPL/TDCM adjuvant effects, which were largely carried out through innate B cells (B-1b and splenic CD23- B cells), were independent of type I IFN signaling. In summary, our study highlights an important role for B-1b cell-expressed IFNAR in promoting responses to nonadjuvanted TI-2 Ags, but it nonetheless demonstrates that adjuvants which support innate B cell responses may bypass this requirement.

Immunoregulation by type I interferons in the peritoneal cavity

The peritoneal cavity, a fluid-containing potential space surrounding the abdominal and pelvic organs, is home to a rich network of immune cells that maintain tissue homeostasis and provide protection against infection. However, under pathological conditions such as peritonitis, endometriosis, and peritoneal carcinomatosis, the peritoneal immune system can become dysregulated, resulting in nonresolving inflammation and disease progression. An enhanced understanding of the factors that regulate peritoneal immune cells under both homeostatic conditions and in disease contexts is therefore required to identify new treatment strategies for these often life-limiting peritoneal pathologies. Type I interferons (T1IFNs) are a family of cytokines with broad immunoregulatory functions, which provide defense against viruses, bacteria, and cancer. There have been numerous reports of immunoregulation by T1IFNs within the peritoneal cavity, which can contribute to both the resolution or propagation of peritoneal disease states, depending on the specifics of the disease setting and local environment. In this review, we provide an overview of the major immune cell populations that reside in the peritoneal cavity (or infiltrate it under inflammatory conditions) and highlight their contribution to the initiation, progression, or resolution of peritoneal diseases. Additionally, we will discuss the role of T1IFNs in the regulation of peritoneal immune cells, and summarize the results of laboratory studies and clinical trials which have investigated T1IFNs in peritonitis/sepsis, endometriosis, and peritoneal carcinomatosis.

A TLR4-TRIF-dependent signaling pathway is required for protective natural tumor-reactive IgM production by B1 cells

Metastatic cancer involving spread to the peritoneal cavity is referred to as peritoneal carcinomatosis and has a very poor prognosis. Our previous studies demonstrated a toll-like receptor 4 (TLR4) and C-type lectin receptor (CLR; Mincle/MCL) agonist pairing of monophosphoryl lipid A (MPL) and trehalose-6,6'-dicorynomycolate (TDCM) effectively inhibits peritoneal tumor growth and ascites development through a mechanism dependent upon B1a cell-produced natural IgM, complement, and phagocytes. In the current study, we investigated the requirement for TLR4 and Fc receptor common γ chain (FcRγ), required for Mincle/MCL signaling, in the MPL/TDCM-elicited response. MPL/TDCM significantly increased macrophages and Ly6Chi monocytes in the peritoneal cavity of both TLR4-/- and FcRγ-/- mice, suggesting redundancy in the signals required for monocyte/macrophage recruitment. However, B1 cell activation, antibody secreting cell differentiation, and tumor-reactive IgM production were defective in TLR4-/-, but not FcRγ-/- mice. TRIF was required for production of IgM reactive against tumor- and mucin-related antigens, but not phosphorylcholine, whereas TLR4 was required for production of both types of reactivities. Consistent with this, B1 cells lacking TLR4 or TRIF did not proliferate or differentiate into tumor-reactive IgM-producing cells in vitro and did not reconstitute MPL/TDCM-dependent protection against peritoneal carcinomatosis in CD19-/- mice. Our results indicate a TLR4/TRIF-dependent pathway is required by B1 cells for MPL/TDCM-elicited production of protective tumor-reactive natural IgM. The dependency on TRIF signaling for tumor-reactive, but not phosphorylcholine-reactive, IgM production reveals unexpected heterogeneity in TLR4-dependent regulation of natural IgM production, thereby highlighting important differences to consider when designing vaccines or therapies targeting these specificities.