[Ontogeny of the immune response in mice. II. Direct hemolytic plaque forming cells and indirect hemolytic plaque forming cells in the spleen of mice antigenically stimulated at various ages].

Investigations were carried out by the direct and indirect haemolytic plaque (DHP and IHP) forming technique in order to determine the capacity of the lymphoid cells of A2G mice fetuses grafted on irradited adults and of mice of different ages, to react after antigenic stimulation with sheep red blood cells, by the synthesis of antibody belonging to the IgM and IgG class. Fetal lymphocytes build up again the lymphoid system of the animals irradiated with lethal doses and develop humoral mediated immune reactions. The sucklings coming in contact with the antigen within the first 20 hours after birth do not synthetize antibodies, and the sucklings stimulated up to the age of 5 days only synthetize antibodies in low amounts. In the spleen of the sucklings stimulated antigenically on day 0 and again on day 10, IgM and not IgG antibody forming cells are predominant. The secondary immune response in the sucklings up to the age of 5 days develops later necessitating a longer period than in the adults or older sucklings. The significance of these results is discussed with reference to the possible biological implications of alpha-proteins.