Antigen

The Antigen chemicals exist in several different varieties, numbered from 0 to 7 in C1. Like the antigens found on the surface of bacteria in the real world, antigens in the Creatures games can be found after bacterial infections.

For each type of antigen, there is a corresponding type of antibody, allowing the creature's immune system to produce the correct antibody against illnesses caused by bacteria. Production of antibodies uses up glucose, and without glucose, antibodies can't be made. (See Brian) In C1, the lower-numbered antigens (0 -4) would use more glucose to make antibodies, and the higher-numbered antigens (5 - 7) would use less glucose. In C1, antibodies would not react with antigens to reduce the concentration of antigens. LummoxJR developed some genes that would do this.

In C3/DS, in addition to differing levels of glucose consumption, production of antibodies can produce mildly toxic side-effects. (See ChiChi Norn Genome gene 346 onwards.) Note that the side effects can differ from genome to genome, for example, in general, the Magma Norns produce more coldness as a side effect, and they do not have hotness as a side effect. Antigens also attack certain organs - if the organs cannot be repaired, the genes governed by those organs switch off.