The Mobile Quarantine Facility (MQF) is a converted Airstream trailer used by NASA to quarantine astronauts returning from Apollo lunar missions. Its purpose was to prevent the spread of any contagions from the moon, though the existence of such contagions was considered unlikely. It functioned by maintaining a lower pressure inside and filtering any air vented.
The MQF contained living and sleeping facilities as well as communications which the astronauts used to converse with their families. The Apollo 11 crew also used this to speak with President Nixon who personally welcomed them back to Earth aboard the recovery ship USS Hornet (CV-12) after splashdown.
The trailers housed the three crew as well as a doctor and an assistant for cleaning and cooking.
Four MQFs were built for NASA:
The quarantine requirement was eliminated following Apollo 14 once it was proven that the moon was void of life (and moon pathogens) and the facilities were no longer necessary.