Adaptive Immunity

Immune System Level

L number

The host's defences mature over a run, shown as an L number by the Detection eye. It sets how big treatment doses get.

• Starts at 1, +1 for every organ you reach, +1 for every Killer T generation you destroy
• Each new level is announced: IMMUNE SYSTEM LEVEL N
• Colour: green at L1, yellow at L2–3, orange at L4–5, red from L6
• Shown once The Immune System Learns is unlocked (skill-tree level 13)

The Immune System Learns

Level 13 unlock

Lean on one shot type and the immune system starts resisting it until you mix things up.

• From Immune Alert 3, it watches your last 20 hits (at least 10 needed)
• If 60% or more were one shot type (Standard, Piercing, Splitting or Explosive), that type deals 30% less damage
• HUD warning: Immune system adapting: <type> resisted
• Influenza A's Antigenic Drift and Shift are natural counters
• Doesn't run in Endless Game Mode

Immunological Memory

Memory

Several cells remember what you did to them and come back better prepared.

• Memory B cells take half damage from the last shot type that hit them
• Dendritic cells that watch you for 2.5 s present your antigen (Detection +18 and the whole room is alerted), then again every 4 s until they die
• Every Killer T generation you destroy returns stronger, with a new skill

Cytokine Storm

From organ 4 (Lymph Node)

The thin hurricane meter under Detection shows how far ahead of the curve your build is. Past its tick mark, the immune system answers with adapted crimson cells.

• Measures whichever is higher: how fast ordinary cells die once you start hitting them (your last 24 kills: it starts filling under about 1.4 s and is full at about 0.35 s), or how little the fighting hurts you (full when you lose under about 6% of your max health per minute of combat; fair is about 35%)
• Starts at the fourth organ (Lymph Node), at any level
• Only reaches full strength once you have 6 traits, so it never kicks in on a fresh run
• CYTOKINE STORM BUILDING warning at 5%; the bar is orange until its tick mark at 30%, then red and pulsing
• A full storm stays full for at least 20 s
• The Lymph Node runs a stricter storm: it counts more lost health as too easy and surges twice as often

Adapted Crimson Cells

Storm response

Past the storm's mark, some newly spawned cells come ADAPTED, marked by a pulsing crimson halo: tougher, faster, harder-hitting and built to beat your defences.

• Up to 45% of new cells adapt at a full storm
• At full strength: 3x health, take 35% less damage, 60% less damage over time (burning, poison, bleeding), move 80% faster, hit 60% harder
• Their hits pierce your defences (PIERCED): shields soak only 30% of them, armor works at reduced strength, and room shield charges don't block them
• Bosses, Killer T cells, antibodies, host cells and tumors never adapt
• First time: CYTOKINE STORM · The immune system responds: crimson cells now resist your build and move faster

Storm Surge

No cap

If the storm stays full, every 20 seconds of fighting it surges a level higher, with no limit.

• Toast: STORM SURGE N · You're still too strong: crimson cells grow tougher and more common
• Each level: more cells adapt (+20% of the base chance, up to 90% of cells), adapted cells get +40% health and hit 25% harder
• Falling back under the storm's tick mark ends the surge

Cytokine Buffs

Buff

Helper T cells and Basophils pulse signals that rile up every cell around them. Buffed cells glow blue.

• Buffed cells move 35% faster and hit 30% harder
• Helper T pulse: radius 220, lasts 4 s, every 4.5 s
• Basophil histamine pulse: radius 200, lasts 2.5 s, every 3.5–4.8 s, and swells you up too
• A new pulse refreshes the buff instead of stacking it

Deeper Organs, Tougher Defences

Escalation

Every organ's immune cells have more health, hit harder and move faster than the last, and the Brain hides behind the blood-brain barrier.

• Cell speed climbs every organ, up to +36% in the Brain
• The Nasal Passage's cells hit softer so new players can learn
• Blood-brain barrier: every cell in the Brain shrugs off 38% of your damage
• In Infect Game Mode, a run that pushes past the organ it started in meets cells with 40% more health and damage per organ beyond it
• Hits on you also grow 4% per Immune Alert step