in: Cell types, Immune cells
Border-associated macrophage
Approved Cell type · facts checked 2 November 2026
Border-associated macrophages (BAMs) are immune cells that live at the brain's borders: the meninges, the spaces around blood vessels and the choroid plexus. In Arborwake, Bram is a border-associated macrophage at Vessel Margins.
In the brain#
The dossier's science anchor is a 2024 review of these cells, simplified here.
- BAMs live in border compartments, not in the brain tissue where microglia live.
- They are distinct from parenchymal microglia and from many blood-derived monocytes.
- Whether a population is replaced from the blood depends on the compartment and the conditions.
- The evidence is mostly lineage tracing and reviews. It does not support a rule that all vessel-side cells are recruited enemies.
In the game#
- Residents, not invaders. The plan's Act II scene II4 is called The visitors belong here. A cell that always lived at the border is not a sign of trouble.
- Identity needs evidence. In Bram's story, a report cannot claim a cell came from the blood just because it sits at the edge. "Identity not established" is a valid result.
- Not microglia. The plan states that Bram is not a microglial variant, and forbids labelling blood-derived macrophages as microglia.
- An optional science note from Bram's story separates microglia, border-associated macrophages and recruited monocytes.
Development#
- Bram began as a candidate in plan v0.5 that needed its own art and biology approval. Bram's identity B and bun body were approved by 2 November.
See also#
Sources#
- .GAME_PLAN/ARBORWAKE_COMPANIONS_NARRATIVE_AND_SYSTEMS_DOSSIER_v0.5.md (working copy, not in Git)
- .GAME_PLAN/ARBORWAKE_THE_LONG_WAKE_COMPLETE_GAME_PLAN_v0.5.md (working copy, not in Git)
16c9aab43:art/characters/named-cast/CANONICAL.json