However, in the context of Mtb infection, it is perhaps the effect of T helper type (Th)1/Th2 polarization on autophagy that is of most interest. Immunity to Mtb is reliant on a
predominantly Th1-biased response, characterized by the localized secretion of interferon (IFN)-γ, TNF-α and interleukin (IL)-12 [13], while Th2 responses in the lungs and periphery of patients, indicated by increased secretion of IL-4 and high antibody titres, have been associated with more severe disease [14,15]. Infection with Mtb results in increased expression of mediators which counteract Th1 responses and promote Th2 responses [16]. Mycobacteria ALK inhibitor cancer have evolved a number of strategies to circumvent the host immune response, including blocking the fusion of phagosomes with lysosomes (phagosome maturation) [17]. However, treatment of Mtb-infected macrophages with IFN-γ can overcome this phagosome maturation block [18,19] and induces autophagy-dependent killing of intracellular mycobacteria [20]. Interestingly, IFN-γ-induced maturation of Mtb-containing phagosomes is abrogated by the TNF blockers adalimumab,
infliximab and etanercept [21], suggesting that the effects of IFN-γ on phagosome maturation, and possibly autophagosome formation, are directed by TNF-α. Indeed, TNF-α induces both phagosome maturation and autophagy in macrophages [12,21], while pre-treatment of human macrophages with IFN-γ increases TNF-α Amrubicin release in response to infection with Mtb[21]. Similarly, ligation of CD40, Dorsomorphin solubility dmso coupled with TNF-α signalling, induces autophagy-dependent killing of Toxoplasma gondii by macrophages [22,23]. While Th1 cytokines have been shown to induce autophagy, the Th2 cytokines IL-4 and IL-13, along with the anti-inflammatory cytokine IL-10 have been shown to inhibit it. IL-4 and
IL-13 have been shown to inhibit autophagy through two separate mechanisms; inhibition of starvation-induced autophagy is dependent on signalling through the protein kinase B (Akt) pathway, while inhibition of IFN-γ-induced autophagy is dependent on signal transducer and activator of transcription (STAT)6 activation [24]. In both cases, treatment of Mtb-infected macrophages with either IL-4 or IL-13 promotes the intracellular survival of the bacteria [24]. Inhibition of rapamycin-induced autophagy by IL-10 is dependent on both Akt and STAT3 [25], while inhibition of starvation-induced autophagy is dependent on type I PI3K/Akt [26]. We have also found that IL-10 inhibits lipopolysaccharide (LPS)-induced autophagy in murine macrophages (Fig. 2). Recent studies have highlighted that autophagy, as well as being modulated by cytokines, can itself regulate secretion of the proinflammatory cytokines IL-1α, IL-1β and IL-18 [27–30]. IL-1β is first produced as a pro-form in response to inflammatory stimuli, including LPS.