MSC Paracrine Immunomodulation Simulator

MSC Dose & Signaling

MSC dose (cells) 15

Secretion potency S 1.00

Diffusion radius σ 2.5

M1 baseline reversion β 0.18

Macrophage Phenotype

M1 (pro-inflammatory): 0M2 (reparative): 0

Mean local factor C

0.00

Healing index

How it works

Much of stem cell therapy's real clinical benefit does not come from transplanted cells differentiating into new tissue — it comes from paracrine signaling: mesenchymal stem cells (MSCs) secrete soluble factors (PGE2, TSG-6, IL-10, IDO) that reprogram the immune cells already at the injury site, rather than replacing them.

Each macrophage carries a polarization state P ∈ [-1, +1], from M1 (pro-inflammatory, P = -1, red) to M2 (reparative/anti-inflammatory, P = +1, green). The local paracrine factor concentration at a macrophage's position is a sum of Gaussian contributions from every MSC:

C_i = S · Σ_j exp( -d_ij² / (2σ²) )

where d_ij is the distance to MSC j, S is secretion potency and σ is the diffusion radius. The polarization state then relaxes toward M2 when local factor is high, and reverts toward M1 at a baseline rate otherwise:

dP_i/dt = α · C_i · (1 - P_i)  -  β · (1 + P_i)

The first term pulls P up toward +1 in proportion to local signal strength; the second term is the spontaneous drift back toward the inflammatory pole (rate β) that dominates far from any MSC. This is exactly why the mechanism is dose- and proximity-dependent: too few MSCs, too little potency, or too short a diffusion radius and the wound stays M1-dominated no matter how long you wait.

MSC dose — how many stem cells are engrafted at the injury site.
Secretion potency S — how much paracrine factor each MSC releases.
Diffusion radius σ — how far the signal reaches before decaying.
Baseline reversion β — how fast an unsignaled macrophage reverts to M1.

Real-world relevance: this trophic/immunomodulatory model is the leading explanation for why MSC infusions help in graft-versus-host disease, osteoarthritis and wound healing even though very few injected cells ever engraft or differentiate long-term.

Mesenchymal stem cell (MSC) M1 macrophage (pro-inflammatory) M2 macrophage (reparative)

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