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Ontogeny of 'macrophage' function. III. Manifestation of high accessory cell activity for primary antibody response by Ia+ functional cells in newborn mouse spleen in collaboration with Ia- macrophages.

The ontogenesis of the responsiveness of murine whole spleen cells in the in vitro primary antibody response paralleled not only the development of competent lymphoid cells but also that of the accessory cell (A-cell) activity of spleen adherent cells (SAC). The Ia+ cell content of SAC (and also peritoneal exudate cells) was very low until 2 weeks of age. The phagocytic activity of macrophages in SAC was higher in newborns than in adults, though no significant difference was observed between Ia- and Ia+ macrophages in phagocytic activity. We attempted to reveal a high A-cell activity using cells in newborn spleen by means of our experimental strategy documented previously in adult mice (Inaba, Nakano & Muramatsu, 1981): though neither Ia- macrophage population (Ia- SAC) nor a temporarily adherent spleen cell population containing few phagocytic macrophages (crude non-macrophage cell fraction, CF) serves as an autonomous A-cell source, the collaboration of Ia+ non-macrophage cells in CF with Ia- SAC causes the manifestation of A-cell activity. Adult CF collaborated as well with newborn SAC as with adult Ia- SAC, indicating that newborn Ia- macrophages are functionally comparable with adult Ia- macrophages in the ability to collaborate with Ia+ non-macrophage cells. On the other hand, a high A-cell activity was generated by the combination of adult Ia- SAC with a large number of newborn CF cells, indicating that there exist competent Ia+ cells in newborn spleen, though much fewer than in adult spleen.