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In general, the concentration of maternal IgG globulin in serum of the neonates falls rapidly within the first few months after birth and the production of IgM globulin develops in the maturing infants during the course of exposure to various antigens in the environment. The development of natural antibodies, ie., isohemagglutinins, IgM class, to ABO blood group substances and agglutinins, Ig class, to normal flora, in the early stage of life is important since not only they may act as bactericidal substances in nonspecific manners, but also could be immunological barometers on the normal function of humoral immune system. The high concentration of isohemagglutinins to human A or B blood group antigens and agglutinating antibodies to some of normal flora such as Propionibacterium acnes or Staphylococcus aureus were observed in normal human sera. It has been known that the serum concentration of IgM globulin usually reached adult levels by one year of age, while that of IgG globulins by five to six years of age. However, the levels of isohemagglutinins to A and B group substances and agglutinating to Propionibacterium acnes in children’s sera and the ages in which the concentrations of their antibodies reached to abult levels are not clarified. In this study, the concentrations of isohemagglutinins to A and B blood group antigens and agglutinating antibodies to P.acnes serotype Ⅰ and serotype Ⅱ in the sera of 163 normal children, ranged from 0 day to 15 years of age, were measured by means of microtitration technique. The results obtained are as follows: 1. In the sera of 163 children under 15 years of age, there observed no significant difference in the titers of agglutinating antibodies to P. acnes serotype Ⅰ andⅡ. 2. Of 75 sera of children under one year of age, the numbers of sera in which agglutinating antibodies were not detectable or less than 1:4 to P. acnes serotype Ⅰ were 67(89.6%) and to serotype Ⅱ 53(70.7%), respectively. 3. Agglutinating antibody to P. acnes serotype Ⅰ in the children’s sera reached adult levels by 7 years of age, but 100 percentages of antibody detection was observed only in the age group of 15 years old, whereas the adult levels of isohemagglutinins to A and B blood group antigens were observed in the age group of 6 months old. 4. No correlation were observed in normal children’s sera between agglutinating antibody titre to P. acnes serotype Ⅰ and isohemagglutinin titre. These results indicated that the isohemagglutinins to ABO blood substances appeared in the earlier stage of life than did agglutinating antibodies to P. acnes.
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