The distinction between innate and adaptive immunity is one of the basic tenets of immunology. The co-operation between these two arms of the immune system is a major determinant of the resistance or susceptibility of the host following pathogen invasion. Hence, this interactive co-operation between cells of the innate and adaptive immunity is of significant interest to immunologists. The sub-population of CD4 + T cells with regulatory phenotype (regulatory T cells; Tregs), which constitute a part of the adaptive immune system, have been widely implicated in the regulation of the immune system and maintenance of immune homeostasis. In the last two decades, there has been an explosion in research describing the role of Tregs and their relevance in several immunopathologies ranging from inflammation to cancer. The majority of these studies focus on the role of Tregs on the cells of the adaptive immune system. Recently, there is significant interest in the role of Tregs on cells of the innate immune system. In this review, we examine the literature on the role of Tregs in immunology. Specifically, we focus on the emerging knowledge of Treg interaction with dendritic cells, macrophages, neutrophils, and γδ T cells. We highlight this interaction as an important link between innate and adaptive immune systems which also indicate the far-reaching role of Tregs in the regulation of immune responses and maintenance of self-tolerance and immune homeostasis.

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It is well established that CD4CD25 regulatory T cells (Tregs) downregulate inflammatory immune responses and help to maintain immune homeostasis. Recent reports have shown that ligation of germline encoded pattern recognition receptors such as Toll-like receptors can stimulate Tregs and therefore implicate Tregs in the pathophysiology of sepsis and other inflammatory diseases. In this report, we show that injection of lipopolysaccharide (LPS) leads to expansion of CD4CD25FoxP3 Tregs, suggesting that these cells may play an important role in immune regulation in LPS-induced acute inflammation. Indeed, genetic or immunological inhibition of Treg function using mice lacking functional Tregs (CD25 KO mice) or anti-CD25 monoclonal antibody (anti-CD25 mAb), respectively, led to acute death in an otherwise nonlethal LPS challenge. This was accompanied by exaggerated production of proinflammatory cytokines. Strikingly, adoptive transfer of CD4CD25 Tregs to CD25 KO mice before LPS challenge rescues mice from death. Unlike LPS, depletion of Tregs followed by concanavalin A (Con A) challenge does not result in mortality, suggesting that Treg depletion does not globally influence all models of acute inflammation. We authenticate our findings by showing that depletion of Tregs leads to mortality in a nonlethal Escherichia coli challenge accompanied by elevated serum levels of proinflammatory cytokines. Collectively, our results indicate that in addition to regulation of LPS-induced acute inflammation, Tregs help to improve bacterial clearance and promote survival in an acute model of bacterial infection.

Cancer stem cells (CSCs) proliferate extensively and drive tumor metastasis and recurrence. CSCs have been identified in over 20 cancer types to date, but it remains unknown how to target and eliminate CSCs in vivo. Aldehyde dehydrogenase (ALDH) is a marker that has been used extensively for isolating CSCs. Here we present a novel approach to target and reduce the frequency of ALDH high CSCs by vaccination against ALDH. We have identified ALDH1-A1 and ALDH1-A3 epitopes from CSCs and developed synthetic high-density lipoprotein nanodiscs for vaccination against ALDH high CSCs. Nanodiscs increased antigen trafficking to lymph nodes and generated robust ALDH-specific T cell responses. Nanodisc vaccination against ALDH high CSCs combined with anti-PD-L1 therapy exerted potent antitumor efficacy and prolonged animal survival in multiple murine models. Overall, this is the first demonstration of a simple nanovaccine strategy against CSCs and may lead to new avenues for cancer immunotherapy against CSCs.

Although diminazene aceturate (Berenil) is widely used as a trypanolytic agent in livestock, its mechanisms of action remain poorly understood. We previously showed that Berenil treatment suppresses pro-inflammatory cytokine production by splenic and liver macrophages leading to a concomitant reduction in serum cytokine levels in mice infected with Trypanosoma congolense or challenged with LPS. Here, we investigated the molecular mechanisms through which Berenil alters pro-inflammatory cytokine production by macrophages. We show that pre-treatment of macrophages with Berenil dramatically suppressed IL-6, IL-12 and TNF-α production following LPS, CpG and Poly I:C stimulation without altering the expression of TLRs. Instead, it significantly down-regulated phosphorylation of mitogen-activated protein kinases (p38, extracellular signal-regulated kinase and c-Jun N-terminal kinases), signal transducer and activator of transcription (STAT) proteins (STAT1 and STAT3) and NF-кB p65 activity both in vitro and in vivo. Interestingly, Berenil treatment up-regulated the phosphorylation of STAT5 and the expression of suppressor of cytokine signaling 1 (SOCS1) and SOCS3, which are negative regulators of innate immune responses, including MAPKs and STATs. Collectively, these results show that Berenil down-regulates macrophage pro-inflammatory cytokine production by inhibiting key signaling pathways associated with cytokine production and suggest that this drug may be used to treat conditions caused by excessive production of inflammatory cytokines.