Systematic review of innate immune responses against Mycobacterium tuberculosis complex infection in animal models

Abstract

Background: Mycobacterium tuberculosis (Mtb) complex (MTBC) includes ten species that affect mammals and pose a significant global health concern. Upon infection, Mtb induces various stages in the host, including early bacterial elimination, which may or may not involve memory responses. Deciphering the role of innate immune responses during MTBC infection is crucial for understanding disease progression or protection. Over the past decade, there has been growing interest in the innate immune response to Mtb, with new preclinical models emerging.

Methods: We conducted a systematic review following PRISMA guidelines, focused on innate immune mediators linked to protection or disease progression in animal models of MTBC infection. We searched two databases: National Library of Medicine and Web of Science. Two researchers independently extracted data based on specific inclusion and exclusion criteria.

Results: Eighty-three articles were reviewed. Results were categorized in four groups: MTBC species, animal models, soluble factors and innate pathways, and other molecules (metabolites and drugs). Mtb and M. bovis were the only species studied. P2X7R receptor's role in disease progression and higher macrophage recruitment were observed differentially after infection with hypervirulent Mtb strains. Mice and non-human primates (NHPs) were the most used mammals, with emerging models like Galleria mellonella and planarians also studied. NHPs provided insights into age-dependent immunity and markers for active tuberculosis (ATB). Key innate immune factors/pathways identified included TNF-α, neutrophil recruitment, ROS/RNS responses, autophagy, inflammasomes, and antimicrobial peptides, with homologous proteins identified in insects. Metabolites like vitamin B5 and prostaglandin E2 were associated with protection. Immunomodulatory drugs targeting autophagy and other mechanisms were studied, exhibiting their potential as therapeutic alternatives.

Conclusion: Simpler, physiologically relevant, and ethically sound models, such as G. mellonella, are needed for studying innate responses in MTBC infection. While insects lack adaptive immunity, they could provide insights into "pure" innate immune responses. The dissection of "pure," "sustained" (later than 7 days post-infection), and trained innate immunity presents additional challenges that require high-resolution temporospatial analytical methods. Identifying early innate immune mediators and targetable pathways in the blood and affected tissues could identify biomarkers for immunization efficiency, disease progression, and potential synergistic therapies for ATB.

Keywords: cytokines; early immunity; in vivo; innate cells; preclinical models; receptors; trained immunity.

Figure 1

PRISMA 2020 flow diagram used in this systematic review (23).

Figure 2

(A) Frequency of animals used in innate response studies against members of the Mycobacterium tuberculosis complex (MTBC), along with the infection routes reported for each animal model. (B) MTBC strains used in the reviewed articles, categorized by animal models. Since mice were the most commonly reported model, the lower section of the figure focuses specifically on MTBC strains used in mice. A total of 83 articles were evaluated. Note that some articles utilized more than one animal model (primarily mice and non-human primates), infection route, or strain, but no studies involving mixed infections were included. Figure created with Biorender.

Figure 3

Early and sustained innate responses found in animals with active TB. (A) Main responses associated with active disease. (B) Responses observed after immunization and after Mycobacterium tuberculosis complex (MTBC) infection in immunized animals (–33). Neutrophil extracellular traps (NETs). ID, intradermal; PMN, Polymorphonuclear leukocyte; fMLP, N-formyl-Methionyl-Leucyl-Phenylalanine; MPO, Myeloperoxidase; Cramp, Cathelicidin-related antimicrobial peptide; ATB, active TB; TNF, Tumoral necrosis factor; IFN, Interferon; MCP-1, monocyte chemotactic protein-1; FOS, Finkel-Biskis-Jinkins osteosarcoma, member of the AP-1 (activator protein-1) family of inducible transcription factors; KLF2, Kruppel-like factor 2; IL, Interleukin; NHP, Non-human primate; MAIT, mucosal-associated invariant T; (PGE2, Prostaglandin E2; LTB4, Leukotriene B4; LXA4, Lipoxin A4; IRF, Interferon regulatory factors; IDO1, indoleamine 2,3-dioxygenase; MMP-9, matrix metallopeptidase 9; iNOs, inducible nitric oxide synthase; PD-L1, programmed death-ligand 1; IM, interstitial macrophages; MdM, monocyte-derived macrophages; BAL, bronchoalveolar lavage; PBMC, Peripheral Blood Mononuclear Cells; C3, Complement 3 protein; NLP3, “NOD-like” receptor (NLR) pyrin domain-containing protein 3; TRIF, Toll/IL-1R domain-containing adaptor-inducing IFN-β; MYD88, myeloid differentiation primary-response 88 protein; d.p.i, days postinfection.

Figure 4

Macrophage receptors and soluble factors identified in response to Mtb complex in the reviewed articles.A. Cytokines, chemokines and receptors identified in the reviewed articles mostly associated with M1 macrophages. (B) Intracellular and endosomal receptors. Some of the recognized molecules (from Mtb or the host) are written in blue in panels (A, B), including TDM: trehalose dimycocerosate (Mtb), ATP: Adenosine triphosphate released from host damaged cells, RD-1 Mtb: region of difference 1, present in virulent Mtb strains, DNA: self (host) and bacterial DNA, NG-MDP: Mycobacterial N-glycolylated muramyl dipeptide. IFN, Interferon; GM-CSF, Granulocyte-monocyte colony-stimulating factor; MIF, Macrophage migration inhibitory factor; IL, interleukin; TGF, Transforming Growth Factor; S1-P, sphingolipid sphingosine-1-phosphate; TLR, Toll-like receptor; iNOS, inducible nitric oxide synthase; IFNGR, Interferon-gamma receptor; MINCLE, Macrophage inducible C-type lectin, also known as CLEC4E; TREM, Triggering receptor expressed on myeloid cells; P2X7R, P2X purinoceptor 7; MHC, Major histocompatibility complex; MCL, macrophage C-type lectin; MCP-1, monocyte chemotactic protein-1; MIP-1α, Macrophage inflammatory protein-1α; CXCL, chemokine (C-X-C motif) ligand; CCL, C-C chemokine ligand; SOCS, Suppressor of cytokine signaling; MMP, Matrix metalloproteinase; miR-20b, microRNA 20b; NLRP3, NOD-like receptor (NLR) pyrin domain-containing protein 3; AIM2, DNA cytosolic sensor “absent in melanoma 2”; NOD, Nucleotide oligomerization domain. Macrophage phenotype classification done following (–143). Created with BioRender.com.