The Immune System

Helper T Cell

Buffer

Hangs back and pulses cytokines that make every nearby cell faster and harder-hitting. Several helpers keep a whole room buffed.

• Base stats: 40 health · 95 speed · 6 touch damage
• Keeps 220–320 points away
• Cytokine pulse every 4.5 s, radius 220: cells inside move 35% faster and hit 30% harder for 4 s
• Organs: Lymph Node, Gut, Bone Marrow
• Also the Follicular Helper T Cell boss's reinforcements, and grown from Lymphoid Progenitors

Thymocyte

Pack

Small, fragile young T cells that drift around you in packs. Every time you dash, every thymocyte nearby dashes straight at you too.

• Base stats: 28 health · 85 speed · 7 touch damage (the smallest lymphocyte)
• Circles 150–230 points from you
• Copies your dash: every thymocyte within 520 points lunges at you
• About a third fail negative selection and die on their own after 6–14 s (FAILED SELECTION)
• Organs: Lymph Node (very common), Brain

Lymphoid Progenitor

Grows up

Slow, weak and harmless at first, with a ring that fills over 6 seconds. When it fills, it becomes a full lymphocyte.

• Base stats: 45 health · 45 speed · 5 touch damage
• Keeps 260–420 points away while its ring fills
• After 6 s: DIFFERENTIATED! It becomes a B cell, NK cell or helper T cell, already hunting you
• 1 time in 10 it becomes a weakened Killer T clone instead
• Organs: Lymph Node, Bone Marrow

Follicular Dendritic Cell

Turret

Doesn't move. It sits in a web that slows you and fires rotating rings of slowing shots.

• Base stats: 90 health · never moves · 8 touch damage
• Its web (radius 150) slows you to 40% speed while you're inside
• Every 3 s within 420 points: a ring of 6 slowing shots (7 damage each)
• Can't roll the Swift, Enraged or Splitting affixes
• Organs: Lymph Node, Brain

Goblet Cell

Lobber

Lobs blobs of mucus at where you're standing: a warning circle, then a sticky puddle that slows you.

• Base stats: 70 health · 50 speed · 8 touch damage
• Only walks toward you when you're more than 260 points away
• Every 3.5 s within 480 points: a 0.8 s warning circle, then the glob lands for 8 damage if you're inside
• Leaves a sticky patch for 7 s that slows you to 20% speed
• Organs: Gut; also the Paneth Cell boss's reinforcements

IgA Plasma Cell

Ranged

Keeps its range and fires spreads of sticky, slowing antibodies.

• Base stats: 60 health · 70 speed · 6 touch damage
• Keeps 260–360 points away
• Every 2.4 s while it can see you within 460 points: a 3-shot spread (7 damage each) that slows you
• Organs: Gut, Liver

Stellate Cell

Area denial

Weaves toward you, leaving patches of scar tissue behind it. The floor gets harder to move on the longer it lives.

• Base stats: 75 health · 70 speed · 12 touch damage
• Drops a patch of scar tissue (fibrosis) every 2.2 s
• Scar tissue lasts 7 s and slows you to 20% speed
• Organs: Liver; also the Kupffer Cell boss's reinforcements

NKT Cell

Stealth

Almost invisible while it stalks you. It appears with a '!' right next to you and lunges for heavy damage, then fades again.

• Base stats: 70 health · 120 speed · 14 touch damage
• Body is only about 12% visible while stalking
• Within 160 points: decloaks with a '!', winds up for 0.4 s, then lunges at high speed
• 2.2 s between strikes
• Organs: Liver, Bone Marrow, Brain

Megakaryocyte

Factory

Huge and tough, it keeps shedding platelet swarms and bursts a ring of fragments when you get close. Kill it to stop the platelets.

• Base stats: 180 health (the toughest regular cell) · 48 speed · 14 touch damage
• Buds 3 platelets every 5 s, up to 9 alive at once
• Within 190 points, every 2.2–3.4 s: it swells, then 0.4 s later bursts a ring of 10 fragments (7 damage each), so hugging it doesn't work
• Organs: Bone Marrow; also Hematopoietic Stem Cell summons

Myeloblast

Rusher

Fast and fragile, it rushes straight at you, and when it dies it bursts into three neutrophils.

• Base stats: 55 health · 105 speed · 9 touch damage
• On death: three half-health neutrophils burst out, already hunting
• Killing it point-blank is risky; kill it from range
• Organs: Bone Marrow; also the Hematopoietic Stem Cell boss's reinforcements and summons

Astrocyte

Support

Hangs back and wraps up to three nearby cells in protective shields, refreshing them as they break.

• Base stats: 85 health · 60 speed · 6 touch damage
• Keeps 240–340 points away
• Every 5 s: shields up to 3 unshielded cells within 260 points, each shield worth 35% of that cell's health
• Never shields bosses
• Organs: Brain; also the Microglia boss's reinforcements and summons

Resident Memory T Cell

Teleporter

Teleports right next to you every few seconds and fires a five-shot burst, with little warning.

• Base stats: 60 health · 90 speed · 10 touch damage (it walks at half speed between blinks)
• Every 3.2 s within 600 points: blinks to a spot about 110 points from you
• 0.35 s later: a 5-shot fan (8 damage each) aimed at you
• Organs: Brain; also Microglia summons

Killer T Cell

Mini-boss

A red, spinning cytotoxic T cell that stalks you, winds up and lunges at high speed. Its pack's health shows in the top bar as KILLER T CELL · GEN N.

• Dispatched when Detection reaches 100, from the Lungs on; in the Nasal Passage only for its introduction
• The organ that introduces it sends the first pack after two cleared fights
• Base stats: 260 health (+4% per Immune Alert step) · 105 speed · 16 touch damage
• Lunge: within 280 points it swells for 0.45 s, then lunges for 0.32 s

Generation 1

Gen 1

A single Killer T cell with one skill: the lunge.

• Pack size: 1
• Lunges every 2.4 s when close

Generation 2

Gen 2

Its lunges now end in a perforin ring.

• Pack size: 1
• Every lunge ends with a ring of 10 perforin shots fired in all directions
• Lunges come slightly more often

Generation 3

Gen 3

Adds homing granzyme shots, and they now hunt in pairs.

• Pack size: 2
• Fires 2 homing granzyme shots every few seconds while it can see you
• Perforin ring grows to 12 shots

Generation 4

Gen 4

Clonal expansion: at half health each one splits off a smaller clone of itself.

• Pack size: 2
• Once per cell, at 50% health: CLONAL EXPANSION spawns a clone with 45% of a full cell's health
• Clones die when the rest of the pack falls
• Perforin ring grows to 14 shots

Generation 5+

Gen 5+

Packs of three with wider granzyme volleys, and every later generation keeps getting tougher and faster.

• Pack size: 3
• Granzyme volleys widen to 3 homing shots
• Perforin ring reaches its maximum of 16 shots
• Lunges speed up each generation, down to one every 1.4 s
• Shot damage grows 15% per generation

The Hunt

Follows you

A Killer T pack follows you through every door, keeping its wounds, until it's destroyed.

• Toast on dispatch: KILLER T CELL DISPATCHED (or N KILLER T CELLS DISPATCHED) with the generation's skill list
• Arrives almost at once through the door or corner farthest from you
• Leave the room and the surviving cells come through after you about 2.5 s later, with the same health and size
• The trail is lost only when you move to the next organ or fall down a drop shaft

Split Copies

On death

Killing a Killer T cell doesn't end it: two smaller, faster copies burst out and keep hunting, and those split once more.

• IT SPLITS! Each split copy has 40% of the health, is 28% smaller, 15% faster and hits 25% softer
• Copies split one more time, so one original can become four tiny hunters
• Only originals drop loot
• The pack only counts as destroyed when every copy is dead

Pack Destroyed

Reward

Wipe out the whole pack and the immune system has to train a stronger generation.

• Toast: KILLER T CELLS DESTROYED
• Detection drops to 20 and is frozen for 10 seconds
• The Immune System Level rises by 1
• The next generation comes the moment Detection maxes out again

Medical Treatment

Detection 75+

Once Detection is 75 or higher, the host may take a treatment. Survive the dose for a reward, or walk out of the room to escape it.

• A 30% chance every 10 seconds while Detection is 75+; never in a boss room
• Warning: INCOMING: <dose> with a coloured tint pulsing over the room for about 2 s
• Dose size grows with the Immune System Level plus one for every dose already given this run; later doses' cells also get 15% more health per earlier dose
• After a dose: at least 2 minutes before the next, 40 s longer after each dose

Antiviral Dose

Dose

Drug capsules flood in with antibodies and neutrophils, and the drug in the blood slows your replication.

• Called ANTIRETROVIRAL DOSE for Retrovirus
• Blurb by virus: Tamiflu (Influenza A), tenofovir (Retrovirus), an Inmazeb antibody infusion (Filovirus), Paxlovid (Halovirus)
• Swarm: 1–3 drug capsules, 8 + 2 per level antibodies, 2 + 1 per level neutrophils
• While it lasts you fire 20% slower everywhere

Booster Shot / PrEP

Dose

Trained antibodies and B cells rush in, shielded by the vaccine. Every cell gets tougher while the dose lasts.

• Called PrEP for Retrovirus
• Swarm: 1–2 vaccine vials (PrEP capsules for Retrovirus), 12 + 3 per level antibodies, B cells and plasmablasts
• While it lasts every immune cell takes 20% less damage

Interferon Shot

Dose

Interferon puts the host on alert: NK cells and antibodies swarm you, and every hit lands harder.

• Swarm: NK cells (3 + 1 per 2 levels), 10 + 3 per level antibodies, neutrophils and monocytes
• While it lasts every hit you take does 25% more damage

Radiation Therapy

Cancer

When cancer has spread into a new organ, there's an even chance the host gets radiation: the tumor shrinks a stage, but it scorches you too.

• 50% chance a few seconds after a metastasis arrives in a new organ
• The tumor drops one growth stage
• You lose 20% of your max health (it can't kill you)
• Radiation sickness for 30 s: 20% less damage and 10% slower movement

Oseltamivir (Tamiflu) Capsule

Medicine

An antiviral capsule that hides behind the nearest crowd of immune cells inside a wide cloud. It heals the cells in its cloud and slows your fire.

• The drug capsule in every run except Retrovirus
• Base stats: 45 health · 85 speed · 7 touch damage
• Cloud radius 240: inside it you fire half as fast as Influenza A (about 40% slower as Filovirus or Halovirus) and move at 75% speed
• HEAL: every 2.5 s it restores 10% health to every immune cell in its cloud

Tenofovir Capsule

Medicine

Retrovirus's antiretroviral capsule. Inside its cloud you fire and move slower, and it boosts the immune cells around it.

• Replaces the Tamiflu capsule in Retrovirus runs
• Cloud radius 240: inside it you fire about 40% slower and move at 75% speed
• BOOST: immune cells in its cloud move 40% faster

Influenza Vaccine Vial

Prevention

A vaccine vial that follows the crowd from behind and projects a large protective ring. Cells inside take only about a third of your damage.

• The vaccine vial in every run except Retrovirus
• Base stats: 70 health · 70 speed · no touch damage
• PROTECT: immune cells inside its 300-point ring take only 35% of your damage
• Organs: Lungs, Bloodstream, Lymph Node, Liver, Bone Marrow, Brain; also Booster Shot doses
• At most one vial per wave

PrEP Capsule

Prevention

Retrovirus's protective capsule. Every few seconds it wraps the immune cells in its ring in shields.

• Replaces the vaccine vial in Retrovirus runs
• SHIELD: every 5 s, cells inside its 300-point ring get a shield worth 25% of their health

Hiding Behind the Crowd

Medicine AI

Drug capsules and vaccine vials work from the back line: the more immune cells around them, the tougher they get, and alone they're very frail.

• They tuck in behind the nearest crowd of up to 6 immune cells, on the far side from you
• They back off whenever you get within 140 points
• With no immune cell in their zone they take 4x damage
• Each cell inside makes them tougher, down to a third of the damage with 8 or more
• Tip: pick off the crowd, or catch them in the open

How Elites Roll

Overview

Every regular cell rolls a tier when it spawns. Deeper organs and a higher Immune Alert make elites far more common.

• Elite odds are halved in the Nasal Passage and climb with every organ, up to 3.5x in the Brain
• The first two rooms of the Nasal Passage never field blue-or-better elites
• From the Lymph Node on almost every cell is at least green; from the Gut on, nearly every regular cell is Rare (blue) or better
• Every 10 Immune Alert steps count like most of an extra organ for elite odds (up to the equivalent of 2.5 organs)

Swift

Affix

Moves much faster than a normal cell of its kind.

• +35% move speed, on top of the tier's own speed bonus
• Never rolled by cells that can't move

Armored

Affix

Carries a grey armor bar that must be broken before its health.

• Armor worth 60% of its max health
• Armor only takes 65% of each hit, so it soaks a lot
• Explosive shots crack armor 60% faster

Shielded

Affix

Wrapped in a cyan shield bubble that soaks damage first.

• Shield worth 40% of its max health
• Breaks before armor and health (SHIELD BROKEN)
• Electric damage (M2 Ion Channel and other electric effects) tears through shields faster

Regenerating

Affix

Heals itself whenever it's left alone.

• After 2 s without being hit it regains 1% of its max health per second
• It can't out-heal steady damage, only recover from neglect

Vampiric

Affix

Heals every time its touch hurts you.

• Each damaging touch heals it 8% of its max health
• Bosses with this affix heal only 2% per touch

Volatile

Affix

Bursts in an explosion when it dies.

• Death blast radius 95 points, 16 base damage to you if you're inside
• Death card: CAUGHT IN AN EXPLOSION

Splitting

Affix

Splits into two smaller copies when it dies.

• Two copies, each 80% size with 30% of the original's max health, already hunting
• Never rolled by bosses, Killer T cells or cells that can't move

Enraged

Affix

Turns red and fiercer once it drops below half health.

• Below 50% health: +30% speed and +40% touch damage (ENRAGED)
• Never rolled by cells that can't move

Awareness & Stealth

Stealth

A fight's first wave waits around the room unaware, wandering near where it started and sweeping a visible sight cone. Stay out of sight to pick your fights.

• Unaware cells show a tinted sight cone and a dim glow
• They see about 250 points inside a roughly 100° cone, and only with a clear line of sight
• They hear you all around within 85 points
• SPOTTED: a '!' appears and every unaware cell within 200 points is alerted in a chain

Ambush

2.5x damage

Catch a cell unaware and your shot hits much harder.

• Your auto-attack targets unaware cells only from 210 points (380 for hunting cells), so you sneak in close
• A hit on an unaware cell deals 2.5x damage and shows AMBUSH
• The hit alerts it, and it starts hunting you
• Killing an unaware cell raises Detection only half as much

Detection

Eye meter

The eye meter at the top right tracks how aware the immune system is of you, from calm green through yellow to pulsing red.

• Base points: a cell spotting you +3; each neighbour it alerts +0.5; every kill +1.2, plus 0.03 more for every kill this run (up to +3 more); getting hit +1; using your signature Shift ability +8 (Influenza A and Filovirus); a wrong step in a receptor puzzle +6; a Dendritic Cell's antigen presentation +18
• Every cell currently hunting you adds a little each second, plus a slow passive creep
• Fills 40% slower in the Nasal Passage and 20% slower in the Lungs than deeper in
• Colour: green below 50, yellow 50–74, red and pulsing from 75
• Cools off once nothing has raised it for 5 s and nothing is hunting you, then drains about 1.2 points a second

Detection Thresholds

Escalation

Each section of the meter brings a bigger immune response.

• 35: first hunter squad
• 60: second hunter squad, bigger
• 75: the host may take a treatment (30% chance every 10 s)
• 80: third hunter squad, bigger still

Hunter Squads

Reinforcements

Cytokines call in a squad of cells that already know where you are, through the door or corner farthest from you.

• Toast: IMMUNE RESPONSE · Cytokines have summoned a hunter squad
• Mostly neutrophils (4 + 1 per organ deep + 1 per squad already sent this run, sometimes one more) plus a B cell
• From the Lungs on: + a Macrophage
• From the Bloodstream on: + an NK cell and a clump of 3 platelets
• Every squad this run is bigger than the last, and gets tougher with Immune Alert

Cooling Down

Lower Detection

Ways to bring Detection back down and shake hunters off your trail.

• Refuge room: heals half your health, drops Detection by 30 and makes every hunting cell lose you (not bosses or Killer T cells)
• Solving a receptor puzzle: Detection -10
• Retrovirus's Latency: Detection -30 and hunters lose your trail
• Coming back from a Dormant Virion (extra life): Detection -25
• Destroying a Killer T pack: Detection drops to 20 and freezes for 10 s

Immune Alert

Run timer

A fever that rises one step every 20 seconds of the run (the flame number in the HUD), making the whole immune system tougher the longer you take.

• Each step: newly spawned cells get 6% more health and every hit on you is 4% stronger
• Boss base health +3% per step, Killer T base health +4% per step
• Raises elite odds (up to the equivalent of 2.5 extra organs at Alert 20)
• At Alert 3 the immune system starts learning your shot types

Fights in Waves

Waves

Fights come in waves: a big placed wave that starts unaware, then smaller reinforcement waves that pour in already hunting.

• Nasal Passage fights have 1 wave (2 deep in the organ); later organs 2 (3 deep in the organ); big rooms add one more and huge rooms another, up to 4
• Reinforcement waves are about 60% the size of the first and spawn away from you
• Every wave adds an antibody swarm on top
• A WAVE N / M pill shows progress

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
• Every Killer T generation you destroy returns stronger, with a new skill

Cytokine Storm

Level 12 unlock

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%)
• 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