The engineer's body was a work of art, all life was a complex interplay of chemical reactions, but within the engineer those reactions weren't so randomly designed. Everything, down to the smallest cell, was as efficient as it could be. Hundreds of different defense and cleaning systems could keep the body operational through all of the worst diseases, poisons, or parasites, and the advanced repair systems would keep the body running as long as there was a body left to run.
This might bring one to wonder what the day to day life was like for the cells in his body, and how they might react to the first test of their defenses.
The engineer had lived in a sterile world without germs, but with the portal opening? Well his immune system would finally fulfill a role beyond purging broken or defective cells.
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It started the way most infections did, the improper following of sanitation protocols. One android entered the one of the recreational rooms, and opened a sealed jar. The sealed nature of the jar had kept the decontaminating lights and chemicals from purging the microbial life within.
Standard sanitation protocols would have been cleaned up within the hour, all the rooms were routinely cleaned by drones and they shined ultraviolet lights on all the surfaces, and the air filtration units had similar measures. This relatively minor breach would have been dealt with, without anyone being the wiser.
There was only one problem, the engineer was in the recreational room, on the minds insistence that he socialize, and he inhaled a whiff of the tainted air.
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U-1146 was doing a routine patrol of the lungs when the alarms went off. This was either a drill, or an invasion, and in either case his mission was clear. Find the invader and neutralize it. His power armor buzzed to full activation and the sensors blasted out through the myriad of blood vessels in the lungs.
He quickly received pings from dozens of red blood cells, platelets and other immune cells, their power armors sensors linking into his to help him narrow down where the infection was.
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It took only a few short moments for the germs to be located, just inside the lungs and trapped within the filters. Helpless to cause any problems but they would still need to be killed, identified, and disposed of.
He ran towards the helpless germs, past checkpoints lined with turrets, dozens of conveyor belts full of oxygen and carbon dioxide, and even more power armored red blood cells. Even if the germs weren't a threat it was still a high alert situation, and he held himself to high standards.
The invaders would be dealt with as soon as possible.
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AE3803 was working in the lungs, well working was a bad way to put it. She was carrying nutrients and metals to the odd new cells that worked to maintain the metal bits of the body she inhabited. They were like platelets, but subtly off and had just shown up one day.
But none of the immune cells had found anything wrong with them, they just requested supplies to repair parts of the body that the other cells had trouble getting too, and then left once those resources or nutrients were delivered. And if they weren't going to cause any problems then AE3803 certainly wasn't going too!
She was interrupted from her internal monologue when her suit informed her she had somehow done a 180 and was now walking the wrong way, she sheepishly turned back around, ignoring the stares from the other cells as she got back on track.
That always seemed to happen, she'd end up heading in entirely the wrong direction, either by getting distracted and making a wrong turn or by some other happenstance. Only the suits recording of where she was going, where she had been, and the optimal path to her destination kept her on schedule.
She still remembered the day they had gotten the suits, all the cells had started filtering through a new organ, one that replaced the decrepit and damaged liver. And when they got there they had each been outfitted with a suit that let them work better. She could have done without the bright purple color though. Red suited her far better.