But although researchers have learned a good deal about how the body's defensive army is organized, they cannot usually predict exactly how the atomic-level interactions between invaders and defenders will play out and thus which alien proteins will stimulate a response. If the engagement of pathogens' proteins with immune cells could be modeled in detail on computers, laboratory-synthesized molecules could rev up the immune system and induce it to attack recalcitrant tumors and fight incipient infections for which no vaccine now exists. The immune system produces thousands of different proteins whose job it is to look out for infiltrators, in any of billions of different combinations.
Infiltrators carry a similarly colossal number of molecular identifiers.
So the number of ways the two might combine is unimaginably huge. Computers easily get bogged down in problems with vast numbers of possibilities. The investigators have determined that the problem can be broken down into smaller bites that can be tackled experimentally. The solutions to the individual bite-size problems can then be combined in a straightforward way. Immune proteins of the type Hammer and his colleagues studied bind to pathogens' proteins as the first step toward triggering a defensive response.