The blood factors I and i in primates including man, and in lower species

Abstract Human‐type blood factors I and i have been investigated in several primate species including man, and in other mammals. The anti‐I tests were performed with the original antiserum which led to the discovery of blood factor I. The anti‐i serum used was obtained from a patient with severe idiopathic hemolytic anemia. Both antisera were similar in serological reactivity, except for their difference of specificity. Human adults, in general, have blood factor I but lack factor i; those very rare adults of type i who lack factor I have the factor i instead. In newborn human infants the factor I is still undeveloped and blood factor i is present in its place. In all other species only juvenile and adult animals have so far been tested. Chimpanzees lack blood factor I but have the factor i, which could be interpreted as phylogeny paralleling ontogeny; however, gibbons lack both factors I and i while orangutan has an intermediate position. All Catarrhini tested, namely, yellow baboons, geladas, patas, mangabeys, macaques, African green, talapoin and Sykes monkeys lack blood factor I but have the factor i. Among Platyrrhini the results are less uniform: Capuchins have very strong blood factor I and a weak factor i, while squirrel and spider monkeys have factor i and little or no factor I. On the other hand, marmosets have both factors I and i well developed. Only two single prosimians were tested: slow loris had factor i but no factor I, while potto lacked both factors I and i. Among non‐primate animals, sheep, goat, deer, cat and South American agoutilack both factors I and i; dog and rat lack factor I but have a weak factor i, while rabbit has a very strong factor I but lacks the factor i. Bearing in mind the relatively small number of animals tested within each species, the present study indicates a heterophile behavior of the blood factors I and i in mammals, in that their distribution cuts across taxonomic lines.