Regulatory B Lymphocytes Colonize the Respiratory Tract of Neonatal Mice and Modulate Immune Responses of Alveolar Macrophages to RSV Infection in IL-10-Dependant Manner

Respiratory syncytial virus (RSV) is the prevalent pathogen of lower respiratory tract infections in children. The presence of neonatal regulatory B lymphocytes (nBreg) has been associated with a poor control of RSV infection in human newborns and with bronchiolitis severity. So far, little is known about how nBreg may contribute to neonatal immunopathology to RSV. We tracked nBreg in neonatal BALB/c mice and we investigated their impact on lung innate immunity, especially their crosstalk with alveolar macrophages (AMs) upon RSV infection. We showed that the colonization by nBreg during the first week of life is a hallmark of neonatal lung whereas this population is almost absent in adult lung. This particular period of age when nBreg are abundant corresponds to the same period when RSV replication in lungs fails to generate a type-I interferons (IFN-I) response and is not contained. When neonatal AMs are exposed to RSV in vitro, they produce IFN-I that in turn enhances IL-10 production by nBreg. IL-10 reciprocally can decrease IFN-I secretion by AMs. Thus, our work identified nBreg as an important component of neonatal lungs and pointed out new immunoregulatory interactions with AMs in the context of RSV infection.

Interleukin 35-Producing Exosomes Suppress Neuroinflammation and Autoimmune Uveitis

Corticosteroids are effective therapy for autoimmune diseases but serious adverse effects preclude their prolonged use. However, immune-suppressive biologics that inhibit lymphoid proliferation are now in use as corticosteroid sparing-agents but with variable success; thus, the need to develop alternative immune-suppressive approaches including cell-based therapies. Efficacy of ex-vivo-generated IL-35-producing regulatory B-cells (i35-Bregs) in suppressing/ameliorating encephalomyelitis or uveitis in mouse models of multiple sclerosis or uveitis, respectively, is therefore a promising therapeutic approach for CNS autoimmune diseases. However, i35-Breg therapy in human uveitis would require producing autologous Bregs from each patient to avoid immune-rejection. Because exosomes exhibit minimal toxicity and immunogenicity, we investigated whether i35-Bregs release exosomes that can be exploited therapeutically. Here, we demonstrate that i35-Bregs release exosomes that contain IL-35 (i35-Exosomes). In this proof-of-concept study, we induced experimental autoimmune uveitis (EAU), monitored EAU progression by fundoscopy, histology, optical coherence tomography and electroretinography, and investigated whether i35-Exosomes treatment would suppress uveitis. Mice treated with i35-Exosomes developed mild EAU with low EAU scores and disease protection correlated with expansion of IL-10 and IL-35 secreting Treg cells with concomitant suppression of Th17 responses. In contrast, significant increase of Th17 cells in vitreous and retina of control mouse eyes was accompanied by severe choroiditis, massive retinal-folds, and photoreceptor cell damage. These hallmark features of severe uveitis were absent in exosome-treated mice and visual impairment detected by ERG was modest compared to control mice. Absence of toxicity or alloreactivity associated with exosomes thus makes i35-Exosomes attractive therapeutic option for delivering IL-35 into CNS tissues.

Infective Larvae of Brugia malayi Induce Polarization of Host Macrophages that Helps in Immune Evasion

Filarial parasites suppress, divert, or polarize the host immune response to aid their survival. However, mechanisms that govern the polarization of host MΦs during early filarial infection are not completely understood. In this study, we infected BALB/c mice with infective larvae stage-3 of Brugia malayi (Bm-L3) and studied their effect on the polarization of splenic MΦs. Results showed that MΦs displayed M2-phenotype by day 3 p.i. characterized by upregulated IL-4, but reduced IL-12 and Prostaglandin-D2 secretion. Increased arginase activity, higher arginase-1 but reduced NOS2 expression and poor phagocytic and antigen processing capacity was also observed. M2 MΦs supported T-cell proliferation and characteristically upregulated p-ERK but downregulated NF-κB-p65 and NF-κB-p50/105. Notably, Bm-L3 synergized with host regulatory T-cells (Tregs) and polarized M2 MΦs to regulatory MΦs (Mregs) by day 7 p.i., which secreted copious amounts of IL-10 and prostaglandin-E2. Mregs also showed upregulated expression levels of MHC-II, CD80, and CD86 and exhibited increased antigen-processing capacity but displayed impaired activation of NF-κB-p65 and NF-κB-p50/105. Neutralization of Tregs by anti-GITR + anti-CD25 antibodies checked the polarization of M2 MΦs to Mregs, decreased accumulation of regulatory B cells and inflammatory monocytes, and reduced secretion of IL-10, but enhanced IL-4 production and percentages of eosinophils, which led to Bm-L3 killing. In summary, we report hitherto undocumented effects of early Bm-L3 infection on the polarization of splenic MΦs and show how infective larvae deftly utilize the functional plasticity of host MΦs to establish themselves inside the host.