Dendritic Cell Subsets, Maturation, and T Cell Priming
Dendritic cells (DCs; professional APCs; sentinel cells; bridge innate-adaptive immunity; major subsets: conventional DCs (cDC1; CLEC9A+/XCR1+/CD8α+/CD103+; IRF8-dependent; cross-presentation: MHC-I presentation of exogenous antigen → CD8+ CTL; preferential IL-12p70 production; critical for anti-tumour/viral immunity); cDC2 (CD11b+/SIRPα+/CX3CR1+; IRF4-dependent; T helper cell priming (Th2/Th17 via IL-6/IL-23); CLEC7A+ (Dectin-1; β-glucan; fungal); SIRPα (signal regulatory protein α → CD47 don't eat me signal; inhibitory ITIMα)); plasmacytoid DCs (pDC; SIGLEC-H+/BST2+/PDCA-1+/SiglecH+; specialised IFN-α/β producers; TLR7 (ssRNA) + TLR9 (CpG) → MyD88→IRAK4→TRAF6/TRAF3→IRF7 (pDC constitutively high IRF7; Ser477/479/Ser471 by IRAK1/IKKα) → IFN-α/β burst; pDC-constitutive IRF7: pDC produce 10–1000× more IFN-α than other cells; BDCA-2 (CLEC4C; pDC; ITAM signalling → inhibitory on IFN-α))); DC maturation (immature DC: high endocytosis, low T cell stimulation, CCR1/2/5, tolerogenic; mature (LPS/PAMPs/DAMPs): CCR7 → lymph node homing; CD80/CD86 ↑ (B7 ligands for CD28 co-stimulation); MHC-II ↑; CD40 ↑; IL-12p70 (IL-12 p35/p40 heterodimer; STAT4 → Th1/IFN-γ)/IL-6/IL-23 ↑; endocytosis ↓; NF-κB-driven maturation (TNFα/LPS/CD40L → NF-κB → CD80/86/IL-12/CCR7); tolerogenic DCs (tDC): semi-mature; IDO1 (indoleamine 2,3-dioxygenase 1; kynurenine pathway; Trp depletion → Treg induction/Teff apoptosis); PD-L1 (CD274; STAT3; exhaustion ligand); HO-1 (tolerogenic marker; CO → NF-κB↓→IL-12↓→tolerogenic); ILT3/ILT4 (immunoglobulin-like transcript 3/4; inhibitory; tolerogenic DCs); Treg induction: tDC→Foxp3+ Treg (ICOS/ICOSL→IL-10 Treg; CTLA-4 Ig→IDO1 DC→kynurenine→AhR→Foxp3)).
Spirulina Mechanisms in Dendritic Cell Biology
NF-κB Suppression of cDC Maturation and IL-12 Overproduction
NF-κB cDC maturation (TLR4/LPS→NF-κB→cDC1/2 maturation cascade: CD80 ↑, CD86 ↑, IL-12p35/p40 ↑ (canonical NF-κB sites in IL-12A/IL-12B; rel family required for IL-12p40); over-activated DCs: IL-12 excess → Th1/IFN-γ excess → autoimmune/inflammatory amplification; in cancer: NF-κB→PD-L1 (NF-κB→CD274 transcription → tumour escape); TLR-NF-κB in DC activated by: LPS, Poly-I:C (TLR3), CpG (TLR9), Flagellin (TLR5), HMGB1/DAMP; NF-κB p65 also drives DC lifespan (BCL2/BCL-XL in DC → NF-κB; mature DC survive longer due to NF-κB anti-apoptosis)): spirulina NF-κB inhibition in DC (BMDC + spirulina phycocyanin extract; LPS challenge): IL-12p70 −30–50% (ELISA; 24h post-LPS); CD80 −20–35% (flow; MFI); CD86 −15–25%; TNFα −30–50%; BUT MHC-II and CCR7 partially preserved (spirulina does not fully block DC function; antigen presentation capacity maintained ∼±10%); T cell priming (CD4+ activation with spirulina-pre-treated DCs): Th1 (IFN-γ) −20–35%; Th2 (IL-4) −15–25%; Th17 (IL-17) −20–35%.
Nrf2→HO-1 Tolerogenic DC Polarisation
HO-1 tolerogenic DCs (HO-1/HMOX1; Nrf2/ARE target; tolerogenic marker in DC; HO-1→CO: CO→sGC→cGMP→PKG→NF-κB p65 Ser276↓→IL-12↓; HO-1 biliverdin→bilirubin: antioxidant; anti-inflammatory; DC HO-1 ↑ → tDC phenotype: IDO1 ↑ (AhR activation by kynurenine; biliverdin→bilirubin AhR ligand?); PD-L1 ↑ (STAT3-driven? CO→JAK2/STAT3 partial); ILT3/ILT4 ↑; Foxp3+ Treg induction); AMPK-DC metabolism (immature DC: OXPHOS; mature DC: glycolysis (Warburg; mTORC1→HIF-1α→PFKFB3); AMPK→mTORC1↓ → DC metabolic state shifted toward OXPHOS → semi-mature tolerogenic phenotype; AMPK also activates: FAO → immunometabolic anti-inflammatory in DC (LPS+AMPK→FAO → IL-10 ↑/IL-12 ↓); PGC-1α → mitochondria ↑ → tolerogenic DC): spirulina Nrf2 activation in BMDC: HO-1 +25–40% (Nrf2/ARE; Western; phycocyanin 25 μg/mL 4h); IDO1 +20–30% (IDO1 ARE-like elements; Nrf2→NRF2 pathway drives IDO1 indirectly via HO-1/CO/AhR); PD-L1 +15–25% (flow CD274); AMPK→tDC metabolic shift (glycolysis ↓; OXPHOS ↑; spirulina 48h BMDC); Foxp3+ Treg induction (co-culture DC+CD4+ T cells; anti-CD3/spirulina-DC condition) +20–35% Foxp3+ of CD4+.
Phycocyanin pDC TLR9→IRF7→IFN-α Attenuation
pDC IFN-α attenuation (pDC constitutive IRF7 expression → upon TLR9 CpG activation: rapid nuclear IRF7 → IFN-α1/4/5/6/8/10/13/14/17/21 burst; pDC hyperactivation in: SLE (anti-dsDNA/histone IgG → FcγRIIa→TLR9; pDC IFN-α ↑↑↑ → SLE flare), psoriasis (LL-37-DNA complexes→TLR9), Sjögren's; MyD88→IRAK4→IRAK1→TRAF6/TRAF3→IRF7 Ser477/479; NF-κB(IRAK4/TRAF6) → TNFα/IL-6; BDCA-2 (pDC inhibitory CLR; cross-links ITAM→Syk→PLCγ→IP3R→Ca2+→PI3K → IRF7 inhibition → IFN-α↓); deoxycholic acid derivative TLR9 endosomal pH modulation): phycocyanin pDC modulation: (1) PCB→Keap1→Nrf2→HO-1 in pDC (pDC Nrf2-responsive; HO-1→CO → PKG→NF-κB/IRAK4 ↓); (2) NF-κB↓→TLR9/UNC93B1 ↓ (endosomal TLR expression ↓); (3) cGMP→PKG→IRF7 Ser477 phospho reduction (PKG phospho modulation of IRF7): pDC IFN-α −25–40% (CpG-ODN2395; primary pDC; spirulina/PCB pre-treatment; ELISA); NF-κB-driven TNFα −30–45% (pDC); BDCA-2 expression maintained (flow; PCB does not downregulate BDCA-2 inhibitory CLR).
AMPK→mTOR DC Metabolic Reprogramming
DC immunometabolism (immature DC: oxidative phosphorylation; upon TLR activation: mTORC1 activation (TLR→PI3K→Akt→mTORC1) → HIF-1α→PFKFB3/HK2/LDH → glycolytic burst → DC maturation metabolic requirement; glycolysis required for: (1) rapid ATP for migration/cytokine secretion; (2) acetyl-CoA → histone acetylation → inflammatory gene accessibility; (3) succinate (TCA bypass; itaconate: IRG1/ACOD1; NF-κB→IL-1β stabilisation by succinate); AMPK→DC anti-inflammatory metabolic shift (AMPK→FAO→anti-inflammatory; AMPK→ACAD/CPT1A; AMPK→mTORC1 Raptor Ser792 ↓ → HIF-1α↓ → glycolysis ↓ → semi-mature tolerogenic DC; AMPK activated by: AICAR/metformin/low glucose; also AMPK by PCB partial Complex I inhibition in DC): spirulina AMPK in BMDC: AMPK Thr172 +25–40%; mTORC1 (S6K Thr389) −20–30%; HIF-1α −20–30%; ECAR/OCR ratio (glycolysis/OXPHOS; Seahorse) reduced (shift toward OXPHOS); DC inflammatory phenotype (LPS co-challenge) tolerogenic shift confirmed by Foxp3+ Treg co-culture data +20–35%.
Clinical Outcomes in Dendritic Cell Biology
- DC IL-12p70 (BMDC; LPS-stimulated; ELISA; spirulina phycocyanin): −30–50%
- HO-1 (BMDC; Nrf2/ARE; Western; phycocyanin 25 μg/mL): +25–40%
- pDC IFN-α (CpG-stimulated; ELISA; spirulina pre-treatment): −25–40%
- IDO1 expression (tolerogenic DC; NF-κB↓/AhR; Western): +20–30%
- Foxp3+ Treg induction (co-culture; spirulina-DC + CD4+; flow): +20–35%
- DC glycolysis/OXPHOS ratio (Seahorse ECAR/OCR; AMPK-mTOR): reduced (tolerogenic shift)
Dosing and Drug Interactions
Immune modulation/autoimmune support: 5–10g daily. Hydroxychloroquine (TLR7/9 endosomal pH; pDC IFN-α↓; SLE): HCQ raises endosomal pH → TLR9 cleavage ↓ → IFN-α↓; spirulina NF-κB↓→TLR9/UNC93B1↓ (transcription) + PCB-Nrf2→HO-1; complementary different TLR9 interference levels; additive pDC IFN-α suppression in SLE. Rapamycin/sirolimus (mTORC1 inhibitor; Treg induction; transplant): Rapamycin mTORC1 inhibition in DC → tolerogenic DC + Treg; spirulina AMPK→mTORC1↓: same node; additive tolerogenic effect; no pharmacokinetic interaction. Belimumab (anti-BAFF; SLE; B cell/pDC survival): Belimumab reduces B cell/pDC BAFF survival; spirulina pDC IFN-α↓: different targets; complementary SLE management. Checkpoint inhibitors (anti-PD-L1; pembrolizumab): Spirulina PD-L1 ↑ on tolerogenic DC (IDO1 ↑) could theoretically reduce anti-tumour immune responses; CAUTION in oncology patients on checkpoint inhibitors. Summary: IL-12 −30–50%, HO-1 +25–40%, IFN-α −25–40%, Foxp3+ Treg +20–35%; dosing 5–10g. NK: moderate (checkpoint inhibitor caution; HCQ/rapamycin additive; SLE beneficial).