Frequency and avidity of specific antigen binding cells in developing mice.J. Exp. Med

In the course of its development, the mouse acquires a large number of lymphoid cells, each committed to make a single type of antibody molecule. Through these molecules, the cells recognize an enormous number of different foreign antigens. Some aspects of the development of this system are fairly well understood. Cells capable of synthesizing immunoglobulin (Ig) can first be detected in the liver on the 12th day of a 19-20 day gestation period (1), but cells bearing surface Ig cannot be detected until the 15th day of gestation when they appear in the spleen and liver (2, 3). The appearance of these Ig-bearing cells in the liver is transient, and they disappear within a week of birth. In the spleen, however, their number continues to increase, reaching a plateau only in the adult animal. The development of antigen-specific cells is less well understood. Although spleen cells specific for each of three antigens have been shown to appear and increase in number in parallel with the development of Ig-bearing cells (2), several investigators have demonstrated that the ability of developing animal