Biphasic Dynamics of Macrophage Immunometabolism during Mycobacterium tuberculosis Infection

Macrophages are the primary targets of Mycobacterium tuberculosis infection; the early events of macrophage interaction with M. tuberculosis define subsequent progression and outcome of infection. M. tuberculosis can alter the innate immunity of macrophages, resulting in suboptimal Th1 immunity, which contributes to the survival, persistence, and eventual dissemination of the pathogen.Macrophages are the primary targets of Mycobacterium tuberculosis infection; the early events of macrophage interaction with M. tuberculosis define subsequent progression and outcome of infection. M. tuberculosis can alter the innate immunity of macrophages, resulting in suboptimal Th1 immunity, which contributes to the survival, persistence, and eventual dissemination of the pathogen. Recent advances in immunometabolism illuminate the intimate link between the metabolic states of immune cells and their specific functions. In this review, we describe the little-studied biphasic metabolic dynamics of the macrophage response during progression of infection by M. tuberculosis and discuss their relevance to macrophage immunity and M. tuberculosis pathogenicity. The early phase of macrophage infection, which is marked by M1 polarization, is accompanied by a metabolic switch from mitochondrial oxidative phosphorylation to hypoxia-inducible factor 1 alpha (HIF-1α)-mediated aerobic glycolysis (also known as the Warburg effect in cancer cells), as well as by an upregulation of pathways involving oxidative and antioxidative defense responses, arginine metabolism, and synthesis of bioactive lipids. These early metabolic changes are followed by a late adaptation/resolution phase in which macrophages transition from glycolysis to mitochondrial oxidative metabolism, with a consequent dampening of macrophage proinflammatory and antimicrobial responses. Importantly, the identification of upregulated metabolic pathways and/or metabolic regulatory mechanisms with immunomodulatory functions during M1 polarization has revealed novel mechanisms of M. tuberculosis pathogenicity. These advances can lead to the development of novel host-directed therapies to facilitate bacterial clearance in tuberculosis by targeting the metabolic state of immune cells

NK cytotoxicity and IFNγ secretion is enhanced after binding to CD72.

<p>(A) ³⁵S-labeled BW or BW/CD72 cells were tested for lysis by activated NK cells at different effectors to targets ratio as indicated in the figure. *p<0.005. (B) ³⁵S-labeled BW/CD72 cells were pre-incubated with the indicated fusion proteins and tested for lysis by activated NK cells at the indicated E:T ratios.*p<0.05. (C) ³⁵S-labeled BW cells were pre-incubated with the indicated fusion proteins and tested for lysis by activated NK cells at the indicated E:T ratios. The differences observed between the various treatments were not statistically significant. (D) NK cells were incubated with BW or BW/CD72 in the presence or absence of the various cytokines indicated in the figure and IFNγ secretion was measured by ELISA. Figure shows one representative experiment out of four performed. * p = 0.03, **p = 0.01</p

172.4 recognize CD100, a 150kDa protein expressed as a homodimer.

<p>(A) Surface radioiodinated YTS cell lysate was immunoprecipitated with mAb 172.4. The immunoprecipitate was analyzed first on non-reducing and then on reducing SDS-PAGE. The left lane is an aliquot of immunoprecipitated proteins resolved under reducing conditions. Molecular weight markers are as shown. The two forms of CD100 (150 and 120 kDa respectively) are indicated with arrows. (B, D) ELISA plates were coated with CD100-Ig and assayed for binding to the indicated antibodies as described in “Materials and Methods”. (C) ELISA plates were coated with CD99-Ig and assayed for binding to the indicated antibodies as described in “Materials and Methods”. The background binding to BSA was subtracted. Figure shows one representative experiment out of four performed. (E) IL-2 activated NK line was stained with either 172.4 or the commercial anti human CD100 antibody A8. FITC conjugated Goat F(ab') anti mouse IgG antibody was used as secondary Ab. Gray histogram is staining with secondary antibody only. Figure show one representative experiment out of 5 performed.</p

The interaction between CD100 and CD72 leads to the phosphorylation of serine residues on proteins associate with CD100.

<p>(A) ³⁵S-labeled activated NK cells were incubated for 20 minutes with adherent BW or BW/CD72 cells. The wells were washed, the remaining cells were lysed and the level of radioactivity was measured in CPM units (counts per mint). The results presented after subtraction of NK cells only. (B) ³⁵S-labeled activated NK cells were incubated for 20 minutes with adherent BW/CD72 cells that were pre incubated with CD100-Ig or CD99-Ig for 2 hr prior to the incubation with NK cells. The wells were washed, the remaining cells were lysed and the level of radioactivity was measured. *p = 0.02. (C) Activated NK cells were incubated with target cells (BW or BW/CD72), in 37°C, for the indicated time periods. Cells were lysed and proteins were immunoprecipitated by mAb 172.4. The immunoprecipitated proteins were separated on a reducing SDS-PAGE. Phosphorylated proteins were detected in western blot by using rabbit anti phospho-serine polyclonal Ab. CD100 levels were detected in western blot by using the A8 anti human CD100. (D) Densitometrical analysis of the level of phosphorylation on serine residues of the three proteins indicated by arrows in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000818#pone-0000818-g005" target="_blank">Figure 5C</a>. The levels of phosphorylation are relative to their level at time zero which was set as one. Figure shows one representative experiment out of two performed.</p

Expression of the ligand of 172.4 on lymphocyte sub-populations and NK line.

<p>Biotinylated 172.4 mAb was used in combination with other fluorescently labeled mAbs in a four color staining. 172.4 staining was detected using Cy-5 streptavidin. Cells were analyzed by flow cytometry. T cells were identified as CD3 positive, NK cells as CD56 positive, CD3 negative, and B cells as CD19 positive. Staining was performed on freshly isolated PBL (A, C and E) and on PBL that were cultured for 72 hr in the presence of IL-2 (100 u/ml) and human serum (B, D and F). Each dot blot shows a gated specific sub-population. An isotype matched antibody was used to determent the background staining for each antibody and is represented in the figure as the horizontal line. (H) Freshly isolated PBMC were incubated for 72 hr with 50 ng/ml of the indicated cytokines. Biotinylated 172.4 mAb was detected using Cy-5 streptavidin and used in combination with other fluorescently labeled mAbs in a four color staining. The PBL were analyzed for the expression of CD100 on NK cells and each dot plot represents a gated NK cells (CD3-, CD56+). Figure shows one representative experiment out of four performed.</p