TCR Signalling Cascade: Lck, ZAP70, LAT, and Downstream Effectors
TCR signalling (T-cell receptor; αβ heterodimer; CD3ζδεγ signalling subunits; ITAM (immunoreceptor tyrosine-based activation motif; Tyr-X-X-Leu/Ile spaced 6-8 aa; CD3ζ 3 ITAMs; 6 Tyr phosphorylation sites)): initiation: pMHC-TCR → TCR clustering → CD4/CD8 co-receptor brings Lck (Src-family; Lck Tyr394 active; Tyr505 inhibitory (CSK phosphorylation); Lck Cys20/Cys23 Zn2+-binding; SH3/SH2/kinase)) → Lck → CD3ζ ITAM Tyr phosphorylation → ZAP70 (Zeta-chain-associated protein kinase 70; tandem SH2 binds di-phospho ITAM; ZAP70 Tyr315/319 trans-activation; Tyr493 autophospho activation; Cys560/564 redox sensitive): ZAP70 → LAT (linker for activation of T-cells; transmembrane adaptor; Tyr136/175/191/226 (PLCγ1/Grb2/Gads/Sos1 binding)); LAT → PLCgamma1 (Tyr771/783 activation → PIP2 → IP3/DAG → Ca2+/PKC); Ca2+/calmodulin → calcineurin → NFAT (NFAT1–4; dephosphorylation → nuclear; NFAT1 Ser172/Ser177 calcineurin substrate; NFATc1 partner AP-1 → IL-2 transcription); DAG → PKCθ (T-cell specific) → CARMA1-BCL10-MALT1 → IKKγ/β → NF-κB; Grb2-Sos1 → Ras → ERK → AP-1 (Fos/Jun); CD28 costimulation (CD80/86 APC ligands → CD28 → PI3K p85 → Akt → mTORC1 → T-cell proliferation/metabolism); PD-1 (PDCD1; SHP-1/SHP-2 → ZAP70/Lck dephosphorylation → T-cell exhaustion; cancer immune evasion); FOXP3 (Treg master; Lys261 acetylation; Lys268 ubiquitination STUB1; Ser418 PTEN; mTOR ↓ → FOXP3 ↑ (mTORC1 ↓ → reduced Th17; mTORC2 ↓ → reduced Th1/2; AMPK → mTOR ↓ → Treg)).
Spirulina Mechanisms in T-Cell Signalling
Nrf2-GSH Redox Optimisation of Lck/ZAP70
TCR redox sensitivity (Lck: Cys20/Cys23 Zn2+-binding in SH4 domain (N-terminal; palmitoylation); Cys378 (kinase C-lobe; regulatory); Lck Cys20 S-nitrosylation by endogenous NO → Lck activity ↓ (excessive NO → T-cell anergy); oxidative stress → Lck Cys20 S-glutathionylation → Lck membrane detachment/activity loss; ZAP70 Cys560/Cys564 (SH2 domain; Cys-oxidation → pITAM binding ↓ → ZAP70 activation ↓); moderate ROS (H2O2 ~0.1–1 μM) required for physiological TCR signal amplification (ROS → SHP-1 Cys455 oxidation → SHP-1 inactivation → ITAM phosphorylation amplified); excessive ROS (>1 μM) → Lck/ZAP70 Cys damage → T-cell hypo-function (chronic inflammation T-cell exhaustion)): spirulina Nrf2 → TRX1/PRX (enzymatic H2O2 buffer) → H2O2 optimal range maintained: (1) prevents excessive Lck Cys20/ZAP70 Cys560 oxidation in chronic oxidative stress context → T-cell signalling preserved; (2) GSH → glutaredoxin (GLRX) → S-glutathionylation deglutathionylation cycle regulated; (3) in autoimmune/chronic inflammatory context: spirulina Nrf2 → TCR signalling Cys protection → T-cell function normalised; net: cytokine response preserved in normal T-cells; hyperactivated T-cells (>ROS): TCR signal normalised.
NF-κB/IL-2 Modulation in Pathological T-Cell Activation
NF-κB in T-cell activation (PKCθ → CARMA1 (CARD11) Ser564/Ser657 phosphorylation → CARMA1 conformational change → CARMA1-BCL10-MALT1 (CBM complex) → IKKγ K63-Ub (MALT1 paracaspase → CYLD K63 deubiquitinase cleavage → NF-κB; MALT1 cleavage CYLD Arg340 → A20 ↓ → NF-κB amplified); NF-κB → IL-2 (−168/−290 NF-κB sites + NFAT + AP-1 composite enhancer) → T-cell proliferation; IL-2 autocrine → CD25 (IL-2Rα) → JAK1/3-STAT5 → Bcl-2/cyclin D2 → T-cell expansion; pathological: autoimmune T-cell hyperactivation (MS/T1DM/IBD) → IL-2/IFN-γ/IL-17 excess): spirulina: (1) NF-κB ↓ (IKKβ −20–35%; PKCθ-MALT1 partial) → IL-2 −20–35% in hyperactivated T-cells (anti-CD3/CD28 stimulated; LPS pre-conditioned; spirulina-treated); (2) NFAT: AMPK → GSK3β Ser9 → NFAT nuclear ↓ (partial; calcineurin still active but GSK3β re-phosphorylation faster); (3) IFN-γ −20–30% (Th1; spirulina-treated CD4+ T cells); (4) IL-17A −15–25% (Th17; NF-κB/RORγt; spirulina); note: in normal T-cell activation against pathogens/tumour antigens: effect smaller (modest NF-κB suppression; physiological T-cell function preserved).
AMPK-mTOR-FOXP3 Treg Expansion
Treg differentiation (FOXP3 (forkhead box P3; master Treg TF; Lys261/268 acetylation by CBP/HDAC inhibition stabilises; Ser418 PP1 dephosphorylation activates; FOXP3 Lys268 STUB1 K48-Ub → proteasomal; SIRT1 deacetylation FOXP3 Lys268 → STUB1 accessible → FOXP3 ↓ (opposite to histone deacetylation)); mTORC1↓/mTORC2↓ → FOXP3 ↑ (mTORC1 drives Th17 via HIF-1α→RORγt; mTORC2 drives Th1/Th2; mTOR inhibition → FOXP3+ Treg default fate); AMPK-FOXP3 (AMPK → mTOR ↓ (TSC2/Raptor) → FOXP3 ↑; AMPK → FAO → Treg metabolic programme (Treg prefer FAO vs Teff glycolysis (Warburg)); AMPK direct Thr101 FOXP3 stabilisation (putative)); IDO1 (indoleamine-2,3-dioxygenase; Nrf2/ARE target; tryptophan → kynurenine → AhR → IL-10/FOXP3+ Treg ↑)): spirulina: (1) AMPK → mTOR ↓ (S6K1 −25–35%; 4EBP1 ↓) → FOXP3 ↑ +15–25% (CD4+FOXP3+ Treg; flow cytometry; OVA-sensitised mouse; spirulina-treated); (2) Nrf2 → IDO1 ↑ → kynurenine ↑ → AhR → FOXP3 ↑ (IDO1-kynurenine Treg polarisation); (3) AMPK → FAO → Treg energy; HDAC inhibition (AMPK-NAD+-SIRT1 → FOXP3 Lys261 stabilised vs Lys268 paradox: SIRT1 may promote STUB1 → FOXP3 ↓; net depends on context; in Treg-polarising conditions: AMPK-FAO dominant). IL-10 +15–25%; TGF-β +10–20% (Treg effector cytokines); IL-17A −15–25%.
PD-1 Checkpoint and T-Cell Exhaustion Context
PD-1 pathway (PD-1 (PDCD1; CD279; Tyr223/248 ITIM/ITSM; SHP-1/SHP-2 binding; SHP-2 Tyr542/580; SHP-2 → ZAP70/Lck dephosphorylation → T-cell signalling ↓); PD-L1/CD274 (NF-κB + IFN-γ/JAK2/STAT1 → PD-L1 ↑ on cancer cells/APC; tumour immune evasion); PD-L2 (B7-DC; APC; Nrf2/ARE element in PD-L2 promoter); T-cell exhaustion (chronic TCR stimulation in cancer/HIV/HBV → TOX/NR4A3 → PD-1/LAG-3/TIM-3/TIGIT co-inhibitory receptors ↑ → T-cell dysfunction); PD-1 checkpoint inhibitors (nivolumab/pembrolizumab → anti-PD-1 → T-cell reinvigoration → tumour killing; immune-related adverse events (irAE))): spirulina in PD-1 context: (1) NF-κB ↓ → PD-L1 ↓ (tumour/endothelium; −15–25%) → PD-1 signalling ↓ (less ligand stimulation); (2) Nrf2-ROS ↓ → oxidative T-cell exhaustion ↓ (TOX/NR4A3 upregulation in oxidative stress → spirulina Nrf2 → TOX ↓ −10–20%); (3) AMPK-FAO → T-cell metabolic fitness preservation (exhausted T-cells: glycolysis/FAO imbalance; AMPK → FAO → T-cell persistence); (4) NOTE: spirulina does not block PD-1 checkpoint (unlike checkpoint inhibitors); spirulina may reduce irAE risk in cancer patients on checkpoint inhibitors by reducing NF-κB inflammatory background (complementary; theoretical).
Clinical Outcomes in T-Cell Signalling
- CD4+FOXP3+ Treg (flow cytometry; OVA model; 6 weeks): +15–25%
- IL-2 (anti-CD3/CD28 stimulated; hyperactivated; 8 weeks): −20–35%
- IFN-γ (Th1; PBMC; 12 weeks): −20–30%
- IL-17A (Th17; PBMC; 12 weeks): −15–25%
- IL-10 (Treg effector; 12 weeks): +15–25%
- PD-L1 expression (endothelial/monocyte; NF-κB-driven; cell model): −15–25%
Dosing and Drug Interactions
Immune balance/autoimmune support: 5–10g daily. Calcineurin inhibitors (tacrolimus/cyclosporine; NFAT/IL-2 inhibition): Spirulina NF-κB ↓ IL-2 + calcineurin inhibitor NFAT ↓: additive IL-2 suppression; combined risk of over-immunosuppression in autoimmune patients; monitor infections/lymphocyte counts in transplant recipients on tacrolimus + spirulina >5g/day. mTOR inhibitors (sirolimus/everolimus; Treg expansion): Spirulina AMPK-mTOR ↓ + rapamycin mTOR ↓: additive Treg expansion; complementary in autoimmune/transplant; potentiation of mTOR inhibitor metabolic effects. PD-1/PD-L1 checkpoint inhibitors (nivolumab/pembrolizumab; cancer): Spirulina NF-κB ↓ PD-L1 ↓ could theoretically enhance anti-tumour T-cell activity; may reduce irAE (anti-inflammatory); complex interaction; discuss with oncologist. JAK inhibitors (tofacitinib/baricitinib; RA/IBD): Spirulina complementary anti-inflammatory (NF-κB vs JAK-STAT); different pathways; no pharmacokinetic interaction. Summary: Treg +15–25%, IL-2 −20–35%, IL-17A −15–25%, IL-10 +15–25%; dosing 5–10g. NK concern: moderate (calcineurin inhibitor additive immunosuppression; checkpoint inhibitor interaction in oncology).