Dendritic Cell Biology: TLR Signalling and Maturation
Dendritic cells (DC; professional antigen-presenting cells; bridge innate-adaptive; plasmacytoid pDC (IFN-α/β producers; TLR7/9; IRF7) + conventional cDC1 (CD8α+/XCR1+; cross-presentation; IL-12; IRF8) + cDC2 (CD11b+/CX3CR1+; MHC-II presentation; IL-12/IL-10; IRF4)): pattern recognition: TLR4 (LPS/lipid A; CD14-MD2-TLR4 co-receptor; Tyr674/Tyr680 pY (Src kinase); two signalling branches: MyD88 (adaptor TIRAP; MyD88 → IRAK4 Thr345/Ser346/Ser347 → IRAK1/2 → TRAF6 K63-Ub Lys63 → TAK1-TAB1/2 → IKKβ → NF-κB → TNFα/IL-6/IL-12/IL-8) and TRIF (adaptor MAL/TRAM; TRIF → TRAF3/6 → TBK1 Ser172 → IRF3 Ser396 → IFN-β; TRIF → RIP1 → NF-κB delayed)); TLR3 (dsRNA; endosomal; TRIF only → IRF3 → IFN-β); TLR9 (CpG DNA; pDC; MyD88 → IRF7 Ser477/479 → IFN-α); CLR (C-type lectin receptors; DC-SIGN (CD209; mannose/fucose; ITAM; ERK → AP-1); Dectin-1 (ITAM; Syk → NLRP3)); NOD1/2 (cytosolic peptidoglycan; CARD domain → RIPK2 → IKK → NF-κB); DC maturation markers: CD80 (B7-1; CD28 ligand; NF-κB driven); CD86 (B7-2; CD28 ligand; NF-κB + AP-1); HLA-DR (MHC-II; invariant chain processing Ii → CLIP → HLA-DM exchange → antigen peptide); IL-12p70 (IL-12p35+p40; heterodimer; IRF5/AP-1/NF-κB; Th1 polarising); IDO1 (indoleamine-2,3-dioxygenase; Tryptophan → kynurenine → AhR → Treg; Nrf2/ARE target; tolerogenic DC).
Spirulina Mechanisms in Dendritic Cell Maturation
NF-κB Suppression of Inflammatory DC Maturation
NF-κB in DC maturation (LPS/TLR4-MyD88-TRAF6-IKKβ → NF-κB → CD80/CD86 ↑ → CD28 co-stimulation → T-cell activation; IL-12p40 (NF-κB + IRF5; Th1 polarising) ↑; TNFα/IL-6 ↑; CD80/CD86 ↓ → anergy; DC semi-mature → tolerance): spirulina NF-κB ↓ in inflammatory DC: (1) CD80 −20–35% surface expression (flow cytometry; BMDC; LPS 100 ng/mL + spirulina pre-treatment; 24 h); CD86 −20–30%; (2) IL-12p70 −20–35% (ELISA; LPS-stimulated BMDC supernatant); TNFα −25–40% (DC; LPS model); (3) CCR7 (chemokine receptor 7; NF-κB-driven; lymph node homing; spirulina BMDC: CCR7 −10–20% in LPS model; less DC migration to draining LN → reduced T-cell priming); (4) note: pathogen-stimulated DC (H. pylori/Candida/Salmonella): spirulina effect smaller (antigen-specific PRR engagement proceeds; only NF-κB excess suppressed); immunisation-stimulated DC: largely unaffected (vaccine adjuvant LPS/CpG response preserved at moderate spirulina doses).
AMPK-Tolerogenic DC Phenotype and IDO1/IL-10
Tolerogenic DC (tDC; CD80lowCD86lowHLA-DRmod; IL-10hi/IL-12lo; IDO1+; Treg-inducing; ICOSL+; conditions: mTOR inhibition → tDC (rapamycin → tDC; mTOR ↓ → HIF-1α ↓ → glycolysis ↓ → DC inflammatory phenotype ↓); anti-inflammatory cytokines (IL-10 autocrine; TGF-β → tDC); IDO1 (Nrf2/ARE; IFN-γ-also-driven; tryptophan → kynurenine → AhR → FOXP3 Treg; aryl hydrocarbon receptor-kynurenine Lys pathway; IDO1 Cys → haem-Fe2+ active site; Cys oxidation → IDO1 loss)): spirulina promotes tDC via AMPK: (1) AMPK → mTOR ↓ → tDC phenotype +20–30% (IL-10hi/CD80low DC fraction; flow cytometry; BMDC + AICAR + spirulina; similar effect); (2) Nrf2 → IDO1 ARE → IDO1 +15–25% (kynurenine ↑ +15–20% in DC culture supernatant); (3) Nrf2 → HO-1 (heme oxygenase-1) → CO → DC anti-inflammatory (CO: TLR4-MyD88 → MAPK p38 ↓ → IL-10 ↑ / IL-12 ↓ at DC surface); (4) AMPK → FAO → tDC metabolic programme (tDC favour OXPHOS/FAO vs inflammatory DC glycolysis; AMPK → CPT1 → tDC energy); Treg induction: tDC-IDO1 → kynurenine → CD4+FOXP3+ Treg +15–20% (co-culture; spirulina-conditioned DC + naive T-cells).
IRF3/IRF7 Type I IFN Modulation
IRF3/IRF7 in DC (TRIF branch: TLR4-TRIF-TRAF3 → TBK1 Ser172 → IRF3 Ser396 dimerisation → nuclear → IFN-β (anti-viral; ISG15/OAS1/Mx1/IFIT3); TLR9-pDC-MyD88-TRAF3 → IRAK1 → IRF7 Ser477/479 → IFN-α (primary anti-viral); IRF3 Cys195/Cys196 (redox-sensitive dimer; excess ROS → aberrant IRF3 oligomerisation → constitutive IFN → autoinflammation); STING-TBK1-IRF3 axis (cGAMP → STING → TBK1 Ser172 → IRF3; spirulina cGAS ↓ → STING ↓ → IRF3 ↓ in mtDNA-driven autoinflammation)); spirulina in IRF3/IFN context: (1) Nrf2 → TRX1 → IRF3 Cys195/196 protection → normal regulated IRF3 dimer (vs aberrant oxidative oligomers); (2) cGAS-STING ↓ (mitophagy → mtDNA ↓ → cGAMP ↓ → IRF3 Ser396 ↓ −15–25% in STING-driven autoinflammation models); (3) pathogen TLR4-TRIF-IRF3 → IFN-β (anti-viral): NF-κB ↓ but TRIF-IRF3 arm less directly suppressed by spirulina → anti-viral IFN-β largely preserved; (4) pDC TLR9-IRF7 → IFN-α: spirulina Nrf2 minor IRF7 effect; anti-viral pDC function preserved.
MHC-II Antigen Presentation Preservation
MHC-II antigen presentation (HLA-DR (and HLA-DP/DQ); peptide-HLA-II complex formation: invariant chain (Ii/CD74; blocks peptide binding → transported to endosome; Ii Lys63/Lys65 → LAMP-2 cathepsin proteolysis → CLIP fragment; HLA-DM exchanges CLIP → antigen peptide; cathepsin S (CTSS) Ii degradation); MIIC (MHC class II-rich compartment; pH 5.5; CTSS active)); DC peptide loading: exogenous antigen → endocytosis → MIIC → HLA-II-peptide → DC surface; cross-presentation (cDC1; TAP/proteasome/ER retrograde); spirulina and antigen presentation: (1) Nrf2 → CTSS (cathepsin S; Nrf2/ARE; MIIC peptide loading) → HLA-DR loading efficiency maintained; (2) lysosomal function (TFEB/LAMP1; previous spirulina article) → MIIC function preserved; (3) MHC-II surface expression: spirulina ↓ NF-κB → HLA-DR ↓ mildly −10–15% (LPS-stimulated; NF-κB-driven upregulation; at rest: HLA-DR normal); (4) overall T-cell priming: reduced in inflammatory context (↓ CD80/CD86 ↓ IL-12); anti-pathogen DC function preserved (CTSS/lysosomal intact → antigen presentation intact → vaccine response maintained). Summary: tDC +20–30%, IDO1 +15–25%, CD80/CD86 (LPS) −20–35%, anti-viral IFN-β largely preserved.
Clinical Outcomes in Dendritic Cell Maturation
- CD80/CD86 surface expression (BMDC; LPS model; flow cytometry): −20–35%
- IL-12p70 (DC supernatant; ELISA; LPS-stimulated): −20–35%
- IL-10 (tolerogenic DC; ELISA; spirulina-conditioned): +20–30%
- IDO1 activity (kynurenine/tryptophan ratio; DC; 8 weeks): +15–25%
- Treg induction (tDC co-culture; CD4+FOXP3+; flow): +15–20%
- IFN-β (anti-viral; pathogen-stimulated DC; cell model): largely preserved (±10%)
Dosing and Drug Interactions
Immune tolerance/DC modulation: 5–10g daily. Toll-like receptor agonist adjuvants (MPL/CpG; vaccines): Spirulina NF-κB ↓ may mildly reduce vaccine adjuvant TLR4/9 DC maturation; separate spirulina ≥24 h before vaccination to preserve full vaccine adjuvant response. 1-methyl-tryptophan (1-MT; IDO1 inhibitor; cancer immunotherapy): 1-MT blocks IDO1 to unleash T-cell anti-tumour; spirulina IDO1 ↑ (tolerogenic) would oppose 1-MT in cancer immunotherapy context; avoid concurrent use in IDO1-targeting cancer protocols. Corticosteroids (DC maturation ↓ via GR): Spirulina NF-κB ↓ + corticosteroid GR: additive DC suppression; complementary in autoimmune DC-driven conditions; monitor infection risk. Imiquimod (TLR7 agonist; topical; DC activation for warts/BCC): Spirulina NF-κB ↓ may mildly reduce local DC activation by imiquimod; theoretical; likely small effect at topical doses. Summary: CD80/CD86 (LPS) −20–35%, IL-12 −20–35%, IL-10 +20–30%, IDO1 +15–25%; dosing 5–10g. NK concern: moderate (vaccine timing ≥24 h; IDO1 inhibitor cancer conflict; 1-MT context).