During tumor progression, macrophages shift their protective M1-phenotype to pro-tumorigenic M2-subtype. Therefore, conversion of M2 to M1 phenotype may be a potential therapeutic intervention. TLRs are important pathogen recognition receptors expressed by cells of the immune system. Recently, a crucial role of TLR-3 has been suggested in cancer. Consequently, in the current study, we defined the role of TLR-3 in the reversion of M2-macrophages to M1. We analyzed the role of TLR-3 stimulation for skewing M2-macrophages to M1 at mRNA and protein level through qRT-PCR, flow cytometry, western blotting, and ELISA. The effectiveness of TLR-3L stimulation to revert M2-macrophages to M1 was evaluated in the murine tumor model. To determine the role of IFN-αβ signaling in vitro and in vivo, we used Ifnar1−/− macrophages and anti-IFN-αβ antibodies, respectively. We observed upregulation of M1-specific markers MHC-II and costimulatory molecules like CD86, CD80, and CD40 on M2-macrophages upon TLR-3 stimulation. In contrast, reduced expression of M2-indicators CD206, Tim-3, and pro-inflammatory cytokines was noticed. The administration of TLR-3L in the murine tumor reverted the M2-macrophages to M1-phenotype and regressed the tumor growth. The mechanism deciphered for macrophage reversion and controlling the tumor growth is dependent on IFN-αβ signaling pathway. The results indicate that the signaling through TLR-3 is important in protection against tumors by skewing M2-macrophages to protective M1-subtype.

Host-directed therapies are gaining considerable impetus because of the emergence of drug-resistant strains of pathogens due to antibiotic therapy. Therefore, there is an urgent need to exploit alternative and novel strategies directed at host molecules to successfully restrict infections. The C-type lectin receptor CLEC4E and Toll-like receptor TLR4 expressed by host cells are among the first line of defense in encountering pathogens. Therefore, we exploited signaling of macrophages through CLEC4E in association with TLR4 agonists (C 4 .T 4 ) to control the growth of Mycobacterium tuberculosis (Mtb). We observed significant improvement in host immunity and reduced bacterial load in the lungs of Mtb-infected mice and guinea pigs treated with C 4 .T 4 agonists. Further, intracellular killing of Mtb was achieved with a 10fold lower dose of isoniazid or rifampicin in conjunction with C 4 .T 4 than the drugs alone. C 4 .T 4 activated MYD88, PtdIns3K, STAT1 and RELA/NFKB, increased lysosome biogenesis, decreased Il10 and Il4 gene expression and enhanced macroautophagy/autophagy. Macrophages from autophagy-deficient (atg5 knockout or Becn1 knockdown) mice showed elevated survival of Mtb. The present findings also unveiled the novel role of CLEC4E in inducing autophagy through MYD88, which is required for control of Mtb growth. This study suggests a unique immunotherapeutic approach involving CLEC4E in conjunction with TLR4 to restrict the survival of Mtb through autophagy.

The mononuclear phagocyte system (MPS) constitutes dendritic cells, monocytes, and macrophages. This system contributes to various functions that are essential for maintaining homeostasis, activation of innate immunity, and bridging it with the adaptive immunity. Consequently, MPS is highly important in bolstering immunity against the pathogens. However, MPS is the frontline cells in destroying Mycobacterium tuberculosis (Mtb), yet the bacterium prefers to reside in the hostile environment of macrophages. Therefore, it may be very interesting to study the struggle between Mtb and MPS to understand the outcome of the disease. In an event when MPS predominates Mtb, the host remains protected. By contrast, the situation becomes devastating when the pathogen tames and tunes the host MPS, which ultimately culminates into tuberculosis (TB). Hence, it becomes extremely crucial to reinvigorate MPS functionality to overwhelm Mtb and eliminate it. In this article, we discuss the strategies to bolster the function of MPS by exploiting the molecules associated with the innate immunity and highlight the mechanisms involved to overcome the Mtb-induced suppression of host immunity. In future, such approaches may provide an insight to develop immunotherapeutics to treat TB.

The global control of tuberculosis (TB) presents a continuous health challenge to mankind. Despite having effective drugs, TB still has a devastating impact on human health. Contributing reasons include the emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb), the AIDS-pandemic, and the absence of effective vaccines against the disease. Indeed, alternative and effective methods of TB treatment and control are urgently needed. One such approach may be to more effectively engage the immune system; particularly the frontline pattern recognition receptor (PRR) systems of the host, which sense pathogen-associated molecular patterns (PAMPs) of Mtb. It is well known that 95% of individuals infected with Mtb in latent form remain healthy throughout their life. Therefore, we propose that clues can be found to control the remainder by successfully manipulating the innate immune mechanisms, particularly of nasal and mucosal cavities. This article highlights the importance of signaling through PRRs in restricting Mtb entry and subsequently preventing its infection. Furthermore, we discuss whether this unique therapy employing PRRs in combination with drugs can help in reducing the dose and duration of current TB regimen.

T cells play a cardinal role in mediating protection against intracellular pathogens like Mycobacterium tuberculosis (Mtb). It is important to understand the factors that govern the T cell response; thereby can modulate its activity. Dendritic cells (DCs) are the major player in initiation and augmentation of T cell response. Targeting DCs to induce their optimum maturation and activation can lead to a better T cell response. Interestingly, we observed that combinatorial signaling of DCs through NOD-2 and TLR-4 fortified better yield of IL-12p40/70, IL-6 and IFN-γ and upregulated the expression of CD40, CD80 and CD86 costimulatory molecules. Further, we noticed improved phagocytic capabilities of DCs. Furthermore, NOD-2 and TLR-4 induced autophagy in DCs, which enhanced the activation of T cells. This study signifies that NOD-2 and TLR-4 exhibit synergism in invigorating the activity of DCs. Consequently, this strategy may have significant immunotherapeutic potential in bolstering the function of DCs and thus improving the immunity against pathogens.